# bpf-helpers

## NAME



           BPF-HELPERS - list of eBPF helper functions
    


## DESCRIPTION



           The extended Berkeley Packet Filter (eBPF) subsystem consists in
           programs written in a pseudo-assembly language, then attached to
           one of the several kernel hooks and run in reaction of specific
           events. This framework differs from the older, "classic" BPF (or
           "cBPF") in several aspects, one of them being the ability to call
           special functions (or "helpers") from within a program.  These
           functions are restricted to a white-list of helpers defined in the
           kernel.
    
           These helpers are used by eBPF programs to interact with the
           system, or with the context in which they work. For instance, they
           can be used to print debugging messages, to get the time since the
           system was booted, to interact with eBPF maps, or to manipulate
           network packets. Since there are several eBPF program types, and
           that they do not run in the same context, each program type can
           only call a subset of those helpers.
    
           Due to eBPF conventions, a helper can not have more than five
           arguments.
    
           Internally, eBPF programs call directly into the compiled helper
           functions without requiring any foreign-function interface. As a
           result, calling helpers introduces no overhead, thus offering
           excellent performance.
    
           This document is an attempt to list and document the helpers
           available to eBPF developers. They are sorted by chronological
           order (the oldest helpers in the kernel at the top).
    


## HELPERS



           **void *bpf_map_lookup_elem(struct bpf_map ***_map_**, const void ***_key_**)**
    
                  **Description**
                         Perform a lookup in _map_ for an entry associated to
                         _key_.
    
                  **Return** Map value associated to _key_ , or **NULL** if no entry was
                         found.
    
           **long bpf_map_update_elem(struct bpf_map ***_map_**, const void ***_key_**,**
           **const void ***_value_**, u64** _flags_**)**
    
                  **Description**
                         Add or update the value of the entry associated to
                         _key_ in _map_ with _value_. _flags_ is one of:
    
                         **BPF_NOEXIST**
                                The entry for _key_ must not exist in the map.
    
                         **BPF_EXIST**
                                The entry for _key_ must already exist in the
                                map.
    
                         **BPF_ANY**
                                No condition on the existence of the entry
                                for _key_.
    
                         Flag value **BPF_NOEXIST** cannot be used for maps of
                         types **BPF_MAP_TYPE_ARRAY** or
                         **BPF_MAP_TYPE_PERCPU_ARRAY**(all elements always
                         exist), the helper would return an error.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_map_delete_elem(struct bpf_map ***_map_**, const void ***_key_**)**
    
                  **Description**
                         Delete entry with _key_ from _map_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_probe_read(void ***_dst_**, u32** _size_**, const void ***_unsafe_ptr_**)**
    
                  **Description**
                         For tracing programs, safely attempt to read _size_
                         bytes from kernel space address _unsafe_ptr_ and store
                         the data in _dst_.
    
                         Generally, use **bpf_probe_read_user**() or
                         **bpf_probe_read_kernel**() instead.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u64 bpf_ktime_get_ns(void)**
    
                  **Description**
                         Return the time elapsed since system boot, in
                         nanoseconds.  Does not include time the system was
                         suspended.  See: **clock_gettime**(**CLOCK_MONOTONIC**)
    
                  **Return** Current _ktime_.
    
           **long bpf_trace_printk(const char ***_fmt_**, u32** _fmt_size_**, ...)**
    
                  **Description**
                         This helper is a "printk()-like" facility for
                         debugging. It prints a message defined by format _fmt_
                         (of size _fmt_size_) to file _/sys/kernel/tracing/trace_
                         from TraceFS, if available. It can take up to three
                         additional **u64** arguments (as an eBPF helpers, the
                         total number of arguments is limited to five).
    
                         Each time the helper is called, it appends a line to
                         the trace.  Lines are discarded while
                         _/sys/kernel/tracing/trace_ is open, use
                         _/sys/kernel/tracing/trace_pipe_ to avoid this.  The
                         format of the trace is customizable, and the exact
                         output one will get depends on the options set in
                         _/sys/kernel/tracing/trace_options_ (see also the
                         _README_ file under the same directory). However, it
                         usually defaults to something like:
    
                            telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>
    
                         In the above:
    
                            • **telnet** is the name of the current task.
    
                            • **470** is the PID of the current task.
    
                            • **001** is the CPU number on which the task is
                              running.
    
                            • In **.N..** , each character refers to a set of
                              options (whether irqs are enabled, scheduling
                              options, whether hard/softirqs are running,
                              level of preempt_disabled respectively). **N**
                              means that **TIF_NEED_RESCHED** and
                              **PREEMPT_NEED_RESCHED** are set.
    
                            • **419421.045894** is a timestamp.
    
                            • **0x00000001** is a fake value used by BPF for the
                              instruction pointer register.
    
                            • **< formatted msg> **is the message formatted with
                              _fmt_.
    
                         The conversion specifiers supported by _fmt_ are
                         similar, but more limited than for printk(). They
                         are **%d** , **%i** , **%u** , **%x** , **%ld** , **%li** , **%lu** , **%lx** , **%lld** , **%lli** ,
                         **%llu** , **%llx** , **%p** , **%s**. No modifier (size of field,
                         padding with zeroes, etc.) is available, and the
                         helper will return **-EINVAL**(but print nothing) if it
                         encounters an unknown specifier.
    
                         Also, note that **bpf_trace_printk**() is slow, and
                         should only be used for debugging purposes. For this
                         reason, a notice block (spanning several lines) is
                         printed to kernel logs and states that the helper
                         should not be used "for production use" the first
                         time this helper is used (or more precisely, when
                         **trace_printk**() buffers are allocated). For passing
                         values to user space, perf events should be
                         preferred.
    
                  **Return** The number of bytes written to the buffer, or a
                         negative error in case of failure.
    
           **u32 bpf_get_prandom_u32(void)**
    
                  **Description**
                         Get a pseudo-random number.
    
                         From a security point of view, this helper uses its
                         own pseudo-random internal state, and cannot be used
                         to infer the seed of other random functions in the
                         kernel. However, it is essential to note that the
                         generator used by the helper is not
                         cryptographically secure.
    
                  **Return** A random 32-bit unsigned value.
    
           **u32 bpf_get_smp_processor_id(void)**
    
                  **Description**
                         Get the SMP (symmetric multiprocessing) processor
                         id. Note that all programs run with migration
                         disabled, which means that the SMP processor id is
                         stable during all the execution of the program.
    
                  **Return** The SMP id of the processor running the program.
    
           **long bpf_skb_store_bytes(struct sk_buff ***_skb_**, u32** _offset_**, const**
           **void ***_from_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Store _len_ bytes from address _from_ into the packet
                         associated to _skb_ , at _offset_. _flags_ are a
                         combination of **BPF_F_RECOMPUTE_CSUM**(automatically
                         recompute the checksum for the packet after storing
                         the bytes) and **BPF_F_INVALIDATE_HASH**(set _skb_**- >hash**,
                         _skb_**- >swhash **and _skb_**- >l4hash **to 0).
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_l3_csum_replace(struct sk_buff ***_skb_**, u32** _offset_**, u64**
           _from_**, u64** _to_**, u64** _size_**)**
    
                  **Description**
                         Recompute the layer 3 (e.g. IP) checksum for the
                         packet associated to _skb_. Computation is
                         incremental, so the helper must know the former
                         value of the header field that was modified (_from_),
                         the new value of this field (_to_), and the number of
                         bytes (2 or 4) for this field, stored in _size_.
                         Alternatively, it is possible to store the
                         difference between the previous and the new values
                         of the header field in _to_ , by setting _from_ and _size_
                         to 0. For both methods, _offset_ indicates the
                         location of the IP checksum within the packet.
    
                         This helper works in combination with
                         **bpf_csum_diff**(), which does not update the checksum
                         in-place, but offers more flexibility and can handle
                         sizes larger than 2 or 4 for the checksum to update.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_l4_csum_replace(struct sk_buff ***_skb_**, u32** _offset_**, u64**
           _from_**, u64** _to_**, u64** _flags_**)**
    
                  **Description**
                         Recompute the layer 4 (e.g. TCP, UDP or ICMP)
                         checksum for the packet associated to _skb_.
                         Computation is incremental, so the helper must know
                         the former value of the header field that was
                         modified (_from_), the new value of this field (_to_),
                         and the number of bytes (2 or 4) for this field,
                         stored on the lowest four bits of _flags_.
                         Alternatively, it is possible to store the
                         difference between the previous and the new values
                         of the header field in _to_ , by setting _from_ and the
                         four lowest bits of _flags_ to 0. For both methods,
                         _offset_ indicates the location of the IP checksum
                         within the packet. In addition to the size of the
                         field, _flags_ can be added (bitwise OR) actual flags.
                         With **BPF_F_MARK_MANGLED_0** , a null checksum is left
                         untouched (unless **BPF_F_MARK_ENFORCE** is added as
                         well), and for updates resulting in a null checksum
                         the value is set to **CSUM_MANGLED_0** instead. Flag
                         **BPF_F_PSEUDO_HDR** indicates the checksum is to be
                         computed against a pseudo-header.
    
                         This helper works in combination with
                         **bpf_csum_diff**(), which does not update the checksum
                         in-place, but offers more flexibility and can handle
                         sizes larger than 2 or 4 for the checksum to update.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_tail_call(void ***_ctx_**, struct bpf_map ***_prog_array_map_**, u32**
           _index_**)**
    
                  **Description**
                         This special helper is used to trigger a "tail
                         call", or in other words, to jump into another eBPF
                         program. The same stack frame is used (but values on
                         stack and in registers for the caller are not
                         accessible to the callee). This mechanism allows for
                         program chaining, either for raising the maximum
                         number of available eBPF instructions, or to execute
                         given programs in conditional blocks. For security
                         reasons, there is an upper limit to the number of
                         successive tail calls that can be performed.
    
                         Upon call of this helper, the program attempts to
                         jump into a program referenced at index _index_ in
                         _prog_array_map_ , a special map of type
                         **BPF_MAP_TYPE_PROG_ARRAY** , and passes _ctx_ , a pointer
                         to the context.
    
                         If the call succeeds, the kernel immediately runs
                         the first instruction of the new program. This is
                         not a function call, and it never returns to the
                         previous program. If the call fails, then the helper
                         has no effect, and the caller continues to run its
                         subsequent instructions. A call can fail if the
                         destination program for the jump does not exist
                         (i.e. _index_ is superior to the number of entries in
                         _prog_array_map_), or if the maximum number of tail
                         calls has been reached for this chain of programs.
                         This limit is defined in the kernel by the macro
                         **MAX_TAIL_CALL_CNT**(not accessible to user space),
                         which is currently set to 33.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_clone_redirect(struct sk_buff ***_skb_**, u32** _ifindex_**, u64**
           _flags_**)**
    
                  **Description**
                         Clone and redirect the packet associated to _skb_ to
                         another net device of index _ifindex_. Both ingress
                         and egress interfaces can be used for redirection.
                         The **BPF_F_INGRESS** value in _flags_ is used to make the
                         distinction (ingress path is selected if the flag is
                         present, egress path otherwise).  This is the only
                         flag supported for now.
    
                         In comparison with **bpf_redirect**() helper,
                         **bpf_clone_redirect**() has the associated cost of
                         duplicating the packet buffer, but this can be
                         executed out of the eBPF program. Conversely,
                         **bpf_redirect**() is more efficient, but it is handled
                         through an action code where the redirection happens
                         only after the eBPF program has returned.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure. Positive error indicates a potential drop
                         or congestion in the target device. The particular
                         positive error codes are not defined.
    
           **u64 bpf_get_current_pid_tgid(void)**
    
                  **Description**
                         Get the current pid and tgid.
    
                  **Return** A 64-bit integer containing the current tgid and
                         pid, and created as such: _current_task_**- >tgid << 32 |**
                         _current_task_**- >pid**.
    
           **u64 bpf_get_current_uid_gid(void)**
    
                  **Description**
                         Get the current uid and gid.
    
                  **Return** A 64-bit integer containing the current GID and UID,
                         and created as such: _current_gid_ **< < 32 |**
                         _current_uid_.
    
           **long bpf_get_current_comm(void ***_buf_**, u32** _size_of_buf_**)**
    
                  **Description**
                         Copy the **comm** attribute of the current task into _buf_
                         of _size_of_buf_. The **comm** attribute contains the name
                         of the executable (excluding the path) for the
                         current task. The _size_of_buf_ must be strictly
                         positive. On success, the helper makes sure that the
                         _buf_ is NUL-terminated. On failure, it is filled with
                         zeroes.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u32 bpf_get_cgroup_classid(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Retrieve the classid for the current task, i.e. for
                         the net_cls cgroup to which _skb_ belongs.
    
                         This helper can be used on TC egress path, but not
                         on ingress.
    
                         The net_cls cgroup provides an interface to tag
                         network packets based on a user-provided identifier
                         for all traffic coming from the tasks belonging to
                         the related cgroup. See also the related kernel
                         documentation, available from the Linux sources in
                         file
                         _Documentation/admin-guide/cgroup-v1/net_cls.rst_.
    
                         The Linux kernel has two versions for cgroups: there
                         are cgroups v1 and cgroups v2. Both are available to
                         users, who can use a mixture of them, but note that
                         the net_cls cgroup is for cgroup v1 only. This makes
                         it incompatible with BPF programs run on cgroups,
                         which is a cgroup-v2-only feature (a socket can only
                         hold data for one version of cgroups at a time).
    
                         This helper is only available is the kernel was
                         compiled with the **CONFIG_CGROUP_NET_CLASSID**
                         configuration option set to "**y** " or to "**m** ".
    
                  **Return** The classid, or 0 for the default unconfigured
                         classid.
    
           **long bpf_skb_vlan_push(struct sk_buff ***_skb_**, __be16** _vlan_proto_**, u16**
           _vlan_tci_**)**
    
                  **Description**
                         Push a _vlan_tci_ (VLAN tag control information) of
                         protocol _vlan_proto_ to the packet associated to _skb_ ,
                         then update the checksum. Note that if _vlan_proto_ is
                         different from **ETH_P_8021Q** and **ETH_P_8021AD** , it is
                         considered to be **ETH_P_8021Q**.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_vlan_pop(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Pop a VLAN header from the packet associated to _skb_.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_get_tunnel_key(struct sk_buff ***_skb_**, struct**
           **bpf_tunnel_key ***_key_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         Get tunnel metadata. This helper takes a pointer _key_
                         to an empty **struct bpf_tunnel_key** of **size** , that will
                         be filled with tunnel metadata for the packet
                         associated to _skb_.  The _flags_ can be set to
                         **BPF_F_TUNINFO_IPV6** , which indicates that the tunnel
                         is based on IPv6 protocol instead of IPv4.
    
                         The **struct bpf_tunnel_key** is an object that
                         generalizes the principal parameters used by various
                         tunneling protocols into a single struct. This way,
                         it can be used to easily make a decision based on
                         the contents of the encapsulation header,
                         "summarized" in this struct. In particular, it holds
                         the IP address of the remote end (IPv4 or IPv6,
                         depending on the case) in _key_**- >remote_ipv4 **or
                         _key_**- >remote_ipv6**. Also, this struct exposes the
                         _key_**- >tunnel_id**, which is generally mapped to a VNI
                         (Virtual Network Identifier), making it programmable
                         together with the **bpf_skb_set_tunnel_key**() helper.
    
                         Let's imagine that the following code is part of a
                         program attached to the TC ingress interface, on one
                         end of a GRE tunnel, and is supposed to filter out
                         all messages coming from remote ends with IPv4
                         address other than 10.0.0.1:
    
                            int ret;
                            struct bpf_tunnel_key key = {};
    
                            ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
                            if (ret < 0)
                                    return TC_ACT_SHOT;     // drop packet
    
                            if (key.remote_ipv4 != 0x0a000001)
                                    return TC_ACT_SHOT;     // drop packet
    
                            return TC_ACT_OK;               // accept packet
    
                         This interface can also be used with all
                         encapsulation devices that can operate in "collect
                         metadata" mode: instead of having one network device
                         per specific configuration, the "collect metadata"
                         mode only requires a single device where the
                         configuration can be extracted from this helper.
    
                         This can be used together with various tunnels such
                         as VXLan, Geneve, GRE or IP in IP (IPIP).
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_set_tunnel_key(struct sk_buff ***_skb_**, struct**
           **bpf_tunnel_key ***_key_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         Populate tunnel metadata for packet associated to
                         _skb._ The tunnel metadata is set to the contents of
                         _key_ , of _size_. The _flags_ can be set to a combination
                         of the following values:
    
                         **BPF_F_TUNINFO_IPV6**
                                Indicate that the tunnel is based on IPv6
                                protocol instead of IPv4.
    
                         **BPF_F_ZERO_CSUM_TX**
                                For IPv4 packets, add a flag to tunnel
                                metadata indicating that checksum computation
                                should be skipped and checksum set to zeroes.
    
                         **BPF_F_DONT_FRAGMENT**
                                Add a flag to tunnel metadata indicating that
                                the packet should not be fragmented.
    
                         **BPF_F_SEQ_NUMBER**
                                Add a flag to tunnel metadata indicating that
                                a sequence number should be added to tunnel
                                header before sending the packet. This flag
                                was added for GRE encapsulation, but might be
                                used with other protocols as well in the
                                future.
    
                         **BPF_F_NO_TUNNEL_KEY**
                                Add a flag to tunnel metadata indicating that
                                no tunnel key should be set in the resulting
                                tunnel header.
    
                         Here is a typical usage on the transmit path:
    
                            struct bpf_tunnel_key key;
                                 populate key ...
                            bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
                            bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
    
                         See also the description of the
                         **bpf_skb_get_tunnel_key**() helper for additional
                         information.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u64 bpf_perf_event_read(struct bpf_map ***_map_**, u64** _flags_**)**
    
                  **Description**
                         Read the value of a perf event counter. This helper
                         relies on a _map_ of type
                         **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the
                         perf event counter is selected when _map_ is updated
                         with perf event file descriptors. The _map_ is an
                         array whose size is the number of available CPUs,
                         and each cell contains a value relative to one CPU.
                         The value to retrieve is indicated by _flags_ , that
                         contains the index of the CPU to look up, masked
                         with **BPF_F_INDEX_MASK**. Alternatively, _flags_ can be
                         set to **BPF_F_CURRENT_CPU** to indicate that the value
                         for the current CPU should be retrieved.
    
                         Note that before Linux 4.13, only hardware perf
                         event can be retrieved.
    
                         Also, be aware that the newer helper
                         **bpf_perf_event_read_value**() is recommended over
                         **bpf_perf_event_read**() in general. The latter has
                         some ABI quirks where error and counter value are
                         used as a return code (which is wrong to do since
                         ranges may overlap). This issue is fixed with
                         **bpf_perf_event_read_value**(), which at the same time
                         provides more features over the
                         **bpf_perf_event_read**() interface. Please refer to the
                         description of **bpf_perf_event_read_value**() for
                         details.
    
                  **Return** The value of the perf event counter read from the
                         map, or a negative error code in case of failure.
    
           **long bpf_redirect(u32** _ifindex_**, u64** _flags_**)**
    
                  **Description**
                         Redirect the packet to another net device of index
                         _ifindex_.  This helper is somewhat similar to
                         **bpf_clone_redirect**(), except that the packet is not
                         cloned, which provides increased performance.
    
                         Except for XDP, both ingress and egress interfaces
                         can be used for redirection. The **BPF_F_INGRESS** value
                         in _flags_ is used to make the distinction (ingress
                         path is selected if the flag is present, egress path
                         otherwise). Currently, XDP only supports redirection
                         to the egress interface, and accepts no flag at all.
    
                         The same effect can also be attained with the more
                         generic **bpf_redirect_map**(), which uses a BPF map to
                         store the redirect target instead of providing it
                         directly to the helper.
    
                  **Return** For XDP, the helper returns **XDP_REDIRECT** on success
                         or **XDP_ABORTED** on error. For other program types,
                         the values are **TC_ACT_REDIRECT** on success or
                         **TC_ACT_SHOT** on error.
    
           **u32 bpf_get_route_realm(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Retrieve the realm or the route, that is to say the
                         **tclassid** field of the destination for the _skb_. The
                         identifier retrieved is a user-provided tag, similar
                         to the one used with the net_cls cgroup (see
                         description for **bpf_get_cgroup_classid**() helper),
                         but here this tag is held by a route (a destination
                         entry), not by a task.
    
                         Retrieving this identifier works with the clsact TC
                         egress hook (see also tc-bpf(8)), or alternatively
                         on conventional classful egress qdiscs, but not on
                         TC ingress path. In case of clsact TC egress hook,
                         this has the advantage that, internally, the
                         destination entry has not been dropped yet in the
                         transmit path. Therefore, the destination entry does
                         not need to be artificially held via
                         **netif_keep_dst**() for a classful qdisc until the _skb_
                         is freed.
    
                         This helper is available only if the kernel was
                         compiled with **CONFIG_IP_ROUTE_CLASSID** configuration
                         option.
    
                  **Return** The realm of the route for the packet associated to
                         _skb_ , or 0 if none was found.
    
           **long bpf_perf_event_output(void ***_ctx_**, struct bpf_map ***_map_**, u64**
           _flags_**, void ***_data_**, u64** _size_**)**
    
                  **Description**
                         Write raw _data_ blob into a special BPF perf event
                         held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**.
                         This perf event must have the following attributes:
                         **PERF_SAMPLE_RAW** as **sample_type** , **PERF_TYPE_SOFTWARE**
                         as **type** , and **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
    
                         The _flags_ are used to indicate the index in _map_ for
                         which the value must be put, masked with
                         **BPF_F_INDEX_MASK**.  Alternatively, _flags_ can be set
                         to **BPF_F_CURRENT_CPU** to indicate that the index of
                         the current CPU core should be used.
    
                         The value to write, of _size_ , is passed through eBPF
                         stack and pointed by _data_.
    
                         The context of the program _ctx_ needs also be passed
                         to the helper.
    
                         On user space, a program willing to read the values
                         needs to call **perf_event_open**() on the perf event
                         (either for one or for all CPUs) and to store the
                         file descriptor into the _map_. This must be done
                         before the eBPF program can send data into it. An
                         example is available in file
                         _samples/bpf/trace_output_user.c_ in the Linux kernel
                         source tree (the eBPF program counterpart is in
                         _samples/bpf/trace_output_kern.c_).
    
                         **bpf_perf_event_output**() achieves better performance
                         than **bpf_trace_printk**() for sharing data with user
                         space, and is much better suitable for streaming
                         data from eBPF programs.
    
                         Note that this helper is not restricted to tracing
                         use cases and can be used with programs attached to
                         TC or XDP as well, where it allows for passing data
                         to user space listeners. Data can be:
    
                         • Only custom structs,
    
                         • Only the packet payload, or
    
                         • A combination of both.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_load_bytes(const void ***_skb_**, u32** _offset_**, void ***_to_**, u32**
           _len_**)**
    
                  **Description**
                         This helper was provided as an easy way to load data
                         from a packet. It can be used to load _len_ bytes from
                         _offset_ from the packet associated to _skb_ , into the
                         buffer pointed by _to_.
    
                         Since Linux 4.7, usage of this helper has mostly
                         been replaced by "direct packet access", enabling
                         packet data to be manipulated with _skb_**- >data **and
                         _skb_**- >data_end **pointing respectively to the first
                         byte of packet data and to the byte after the last
                         byte of packet data. However, it remains useful if
                         one wishes to read large quantities of data at once
                         from a packet into the eBPF stack.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_get_stackid(void ***_ctx_**, struct bpf_map ***_map_**, u64** _flags_**)**
    
                  **Description**
                         Walk a user or a kernel stack and return its id. To
                         achieve this, the helper needs _ctx_ , which is a
                         pointer to the context on which the tracing program
                         is executed, and a pointer to a _map_ of type
                         **BPF_MAP_TYPE_STACK_TRACE**.
    
                         The last argument, _flags_ , holds the number of stack
                         frames to skip (from 0 to 255), masked with
                         **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to
                         set a combination of the following flags:
    
                         **BPF_F_USER_STACK**
                                Collect a user space stack instead of a
                                kernel stack.
    
                         **BPF_F_FAST_STACK_CMP**
                                Compare stacks by hash only.
    
                         **BPF_F_REUSE_STACKID**
                                If two different stacks hash into the same
                                _stackid_ , discard the old one.
    
                         The stack id retrieved is a 32 bit long integer
                         handle which can be further combined with other data
                         (including other stack ids) and used as a key into
                         maps. This can be useful for generating a variety of
                         graphs (such as flame graphs or off-cpu graphs).
    
                         For walking a stack, this helper is an improvement
                         over **bpf_probe_read**(), which can be used with
                         unrolled loops but is not efficient and consumes a
                         lot of eBPF instructions.  Instead,
                         **bpf_get_stackid**() can collect up to
                         **PERF_MAX_STACK_DEPTH** both kernel and user frames.
                         Note that this limit can be controlled with the
                         **sysctl** program, and that it should be manually
                         increased in order to profile long user stacks (such
                         as stacks for Java programs). To do so, use:
    
                            # sysctl kernel.perf_event_max_stack=<new value>
    
                  **Return** The positive or null stack id on success, or a
                         negative error in case of failure.
    
           **s64 bpf_csum_diff(__be32 ***_from_**, u32** _from_size_**, __be32 ***_to_**, u32**
           _to_size_**, __wsum** _seed_**)**
    
                  **Description**
                         Compute a checksum difference, from the raw buffer
                         pointed by _from_ , of length _from_size_ (that must be a
                         multiple of 4), towards the raw buffer pointed by
                         _to_ , of size _to_size_ (same remark). An optional _seed_
                         can be added to the value (this can be cascaded, the
                         seed may come from a previous call to the helper).
    
                         This is flexible enough to be used in several ways:
    
                         • With _from_size_ == 0, _to_size_ > 0 and _seed_ set to
                           checksum, it can be used when pushing new data.
    
                         • With _from_size_ > 0, _to_size_ == 0 and _seed_ set to
                           checksum, it can be used when removing data from a
                           packet.
    
                         • With _from_size_ > 0, _to_size_ > 0 and _seed_ set to 0,
                           it can be used to compute a diff. Note that
                           _from_size_ and _to_size_ do not need to be equal.
    
                         This helper can be used in combination with
                         **bpf_l3_csum_replace**() and **bpf_l4_csum_replace**(), to
                         which one can feed in the difference computed with
                         **bpf_csum_diff**().
    
                  **Return** The checksum result, or a negative error code in
                         case of failure.
    
           **long bpf_skb_get_tunnel_opt(struct sk_buff ***_skb_**, void ***_opt_**, u32**
           _size_**)**
    
                  **Description**
                         Retrieve tunnel options metadata for the packet
                         associated to _skb_ , and store the raw tunnel option
                         data to the buffer _opt_ of _size_.
    
                         This helper can be used with encapsulation devices
                         that can operate in "collect metadata" mode (please
                         refer to the related note in the description of
                         **bpf_skb_get_tunnel_key**() for more details). A
                         particular example where this can be used is in
                         combination with the Geneve encapsulation protocol,
                         where it allows for pushing (with
                         **bpf_skb_get_tunnel_opt**() helper) and retrieving
                         arbitrary TLVs (Type-Length-Value headers) from the
                         eBPF program. This allows for full customization of
                         these headers.
    
                  **Return** The size of the option data retrieved.
    
           **long bpf_skb_set_tunnel_opt(struct sk_buff ***_skb_**, void ***_opt_**, u32**
           _size_**)**
    
                  **Description**
                         Set tunnel options metadata for the packet
                         associated to _skb_ to the option data contained in
                         the raw buffer _opt_ of _size_.
    
                         See also the description of the
                         **bpf_skb_get_tunnel_opt**() helper for additional
                         information.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_change_proto(struct sk_buff ***_skb_**, __be16** _proto_**, u64**
           _flags_**)**
    
                  **Description**
                         Change the protocol of the _skb_ to _proto_. Currently
                         supported are transition from IPv4 to IPv6, and from
                         IPv6 to IPv4. The helper takes care of the
                         groundwork for the transition, including resizing
                         the socket buffer. The eBPF program is expected to
                         fill the new headers, if any, via **skb_store_bytes**()
                         and to recompute the checksums with
                         **bpf_l3_csum_replace**() and **bpf_l4_csum_replace**(). The
                         main case for this helper is to perform NAT64
                         operations out of an eBPF program.
    
                         Internally, the GSO type is marked as dodgy so that
                         headers are checked and segments are recalculated by
                         the GSO/GRO engine.  The size for GSO target is
                         adapted as well.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_change_type(struct sk_buff ***_skb_**, u32** _type_**)**
    
                  **Description**
                         Change the packet type for the packet associated to
                         _skb_. This comes down to setting _skb_**- >pkt_type **to
                         _type_ , except the eBPF program does not have a write
                         access to _skb_**- >pkt_type **beside this helper. Using a
                         helper here allows for graceful handling of errors.
    
                         The major use case is to change incoming _skb*s to_
                         _**PACKET_HOST*_ in a programmatic way instead of
                         having to recirculate via **redirect**(...,
                         **BPF_F_INGRESS**), for example.
    
                         Note that _type_ only allows certain values. At this
                         time, they are:
    
                         **PACKET_HOST**
                                Packet is for us.
    
                         **PACKET_BROADCAST**
                                Send packet to all.
    
                         **PACKET_MULTICAST**
                                Send packet to group.
    
                         **PACKET_OTHERHOST**
                                Send packet to someone else.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_under_cgroup(struct sk_buff ***_skb_**, struct bpf_map**
           *****_map_**, u32** _index_**)**
    
                  **Description**
                         Check whether _skb_ is a descendant of the cgroup2
                         held by _map_ of type **BPF_MAP_TYPE_CGROUP_ARRAY** , at
                         _index_.
    
                  **Return** The return value depends on the result of the test,
                         and can be:
    
                         • 0, if the _skb_ failed the cgroup2 descendant test.
    
                         • 1, if the _skb_ succeeded the cgroup2 descendant
                           test.
    
                         • A negative error code, if an error occurred.
    
           **u32 bpf_get_hash_recalc(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Retrieve the hash of the packet, _skb_**- >hash**. If it is
                         not set, in particular if the hash was cleared due
                         to mangling, recompute this hash. Later accesses to
                         the hash can be done directly with _skb_**- >hash**.
    
                         Calling **bpf_set_hash_invalid**(), changing a packet
                         prototype with **bpf_skb_change_proto**(), or calling
                         **bpf_skb_store_bytes**() with the **BPF_F_INVALIDATE_HASH**
                         are actions susceptible to clear the hash and to
                         trigger a new computation for the next call to
                         **bpf_get_hash_recalc**().
    
                  **Return** The 32-bit hash.
    
           **u64 bpf_get_current_task(void)**
    
                  **Description**
                         Get the current task.
    
                  **Return** A pointer to the current task struct.
    
           **long bpf_probe_write_user(void ***_dst_**, const void ***_src_**, u32** _len_**)**
    
                  **Description**
                         Attempt in a safe way to write _len_ bytes from the
                         buffer _src_ to _dst_ in memory. It only works for
                         threads that are in user context, and _dst_ must be a
                         valid user space address.
    
                         This helper should not be used to implement any kind
                         of security mechanism because of TOC-TOU attacks,
                         but rather to debug, divert, and manipulate
                         execution of semi-cooperative processes.
    
                         Keep in mind that this feature is meant for
                         experiments, and it has a risk of crashing the
                         system and running programs.  Therefore, when an
                         eBPF program using this helper is attached, a
                         warning including PID and process name is printed to
                         kernel logs.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_current_task_under_cgroup(struct bpf_map ***_map_**, u32** _index_**)**
    
                  **Description**
                         Check whether the probe is being run is the context
                         of a given subset of the cgroup2 hierarchy. The
                         cgroup2 to test is held by _map_ of type
                         **BPF_MAP_TYPE_CGROUP_ARRAY** , at _index_.
    
                  **Return** The return value depends on the result of the test,
                         and can be:
    
                         • 1, if current task belongs to the cgroup2.
    
                         • 0, if current task does not belong to the cgroup2.
    
                         • A negative error code, if an error occurred.
    
           **long bpf_skb_change_tail(struct sk_buff ***_skb_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Resize (trim or grow) the packet associated to _skb_
                         to the new _len_. The _flags_ are reserved for future
                         usage, and must be left at zero.
    
                         The basic idea is that the helper performs the
                         needed work to change the size of the packet, then
                         the eBPF program rewrites the rest via helpers like
                         **bpf_skb_store_bytes**(), **bpf_l3_csum_replace**(),
                         **bpf_l3_csum_replace**() and others. This helper is a
                         slow path utility intended for replies with control
                         messages. And because it is targeted for slow path,
                         the helper itself can afford to be slow: it
                         implicitly linearizes, unclones and drops offloads
                         from the _skb_.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_pull_data(struct sk_buff ***_skb_**, u32** _len_**)**
    
                  **Description**
                         Pull in non-linear data in case the _skb_ is
                         non-linear and not all of _len_ are part of the linear
                         section. Make _len_ bytes from _skb_ readable and
                         writable. If a zero value is passed for _len_ , then
                         all bytes in the linear part of _skb_ will be made
                         readable and writable.
    
                         This helper is only needed for reading and writing
                         with direct packet access.
    
                         For direct packet access, testing that offsets to
                         access are within packet boundaries (test on
                         _skb_**- >data_end**) is susceptible to fail if offsets are
                         invalid, or if the requested data is in non-linear
                         parts of the _skb_. On failure the program can just
                         bail out, or in the case of a non-linear buffer, use
                         a helper to make the data available. The
                         **bpf_skb_load_bytes**() helper is a first solution to
                         access the data. Another one consists in using
                         **bpf_skb_pull_data** to pull in once the non-linear
                         parts, then retesting and eventually access the
                         data.
    
                         At the same time, this also makes sure the _skb_ is
                         uncloned, which is a necessary condition for direct
                         write. As this needs to be an invariant for the
                         write part only, the verifier detects writes and
                         adds a prologue that is calling **bpf_skb_pull_data()**
                         to effectively unclone the _skb_ from the very
                         beginning in case it is indeed cloned.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **s64 bpf_csum_update(struct sk_buff ***_skb_**, __wsum** _csum_**)**
    
                  **Description**
                         Add the checksum _csum_ into _skb_**- >csum **in case the
                         driver has supplied a checksum for the entire packet
                         into that field. Return an error otherwise. This
                         helper is intended to be used in combination with
                         **bpf_csum_diff**(), in particular when the checksum
                         needs to be updated after data has been written into
                         the packet through direct packet access.
    
                  **Return** The checksum on success, or a negative error code in
                         case of failure.
    
           **void bpf_set_hash_invalid(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Invalidate the current _skb_**- >hash**. It can be used
                         after mangling on headers through direct packet
                         access, in order to indicate that the hash is
                         outdated and to trigger a recalculation the next
                         time the kernel tries to access this hash or when
                         the **bpf_get_hash_recalc**() helper is called.
    
                  **Return** void.
    
           **long bpf_get_numa_node_id(void)**
    
                  **Description**
                         Return the id of the current NUMA node. The primary
                         use case for this helper is the selection of sockets
                         for the local NUMA node, when the program is
                         attached to sockets using the
                         **SO_ATTACH_REUSEPORT_EBPF** option (see also
                         socket(7)), but the helper is also available to
                         other eBPF program types, similarly to
                         **bpf_get_smp_processor_id**().
    
                  **Return** The id of current NUMA node.
    
           **long bpf_skb_change_head(struct sk_buff ***_skb_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Grows headroom of packet associated to _skb_ and
                         adjusts the offset of the MAC header accordingly,
                         adding _len_ bytes of space. It automatically extends
                         and reallocates memory as required.
    
                         This helper can be used on a layer 3 _skb_ to push a
                         MAC header for redirection into a layer 2 device.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_xdp_adjust_head(struct xdp_buff ***_xdp_md_**, int** _delta_**)**
    
                  **Description**
                         Adjust (move) _xdp_md_**- >data **by _delta_ bytes. Note that
                         it is possible to use a negative value for _delta_.
                         This helper can be used to prepare the packet for
                         pushing or popping headers.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_probe_read_str(void ***_dst_**, u32** _size_**, const void**
           *****_unsafe_ptr_**)**
    
                  **Description**
                         Copy a NUL terminated string from an unsafe kernel
                         address _unsafe_ptr_ to _dst_. See
                         **bpf_probe_read_kernel_str**() for more details.
    
                         Generally, use **bpf_probe_read_user_str**() or
                         **bpf_probe_read_kernel_str**() instead.
    
                  **Return** On success, the strictly positive length of the
                         string, including the trailing NUL character. On
                         error, a negative value.
    
           **u64 bpf_get_socket_cookie(struct sk_buff ***_skb_**)**
    
                  **Description**
                         If the **struct sk_buff** pointed by _skb_ has a known
                         socket, retrieve the cookie (generated by the
                         kernel) of this socket.  If no cookie has been set
                         yet, generate a new cookie. Once generated, the
                         socket cookie remains stable for the life of the
                         socket. This helper can be useful for monitoring per
                         socket networking traffic statistics as it provides
                         a global socket identifier that can be assumed
                         unique.
    
                  **Return** A 8-byte long unique number on success, or 0 if the
                         socket field is missing inside _skb_.
    
           **u64 bpf_get_socket_cookie(struct bpf_sock_addr ***_ctx_**)**
    
                  **Description**
                         Equivalent to bpf_get_socket_cookie() helper that
                         accepts _skb_ , but gets socket from **struct**
                         **bpf_sock_addr** context.
    
                  **Return** A 8-byte long unique number.
    
           **u64 bpf_get_socket_cookie(struct bpf_sock_ops ***_ctx_**)**
    
                  **Description**
                         Equivalent to **bpf_get_socket_cookie**() helper that
                         accepts _skb_ , but gets socket from **struct**
                         **bpf_sock_ops** context.
    
                  **Return** A 8-byte long unique number.
    
           **u64 bpf_get_socket_cookie(struct sock ***_sk_**)**
    
                  **Description**
                         Equivalent to **bpf_get_socket_cookie**() helper that
                         accepts _sk_ , but gets socket from a BTF **struct sock**.
                         This helper also works for sleepable programs.
    
                  **Return** A 8-byte long unique number or 0 if _sk_ is NULL.
    
           **u32 bpf_get_socket_uid(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Get the owner UID of the socked associated to _skb_.
    
                  **Return** The owner UID of the socket associated to _skb_. If
                         the socket is **NULL** , or if it is not a full socket
                         (i.e. if it is a time-wait or a request socket
                         instead), **overflowuid** value is returned (note that
                         **overflowuid** might also be the actual UID value for
                         the socket).
    
           **long bpf_set_hash(struct sk_buff ***_skb_**, u32** _hash_**)**
    
                  **Description**
                         Set the full hash for _skb_ (set the field _skb_**- >hash**)
                         to value _hash_.
    
                  **Return** 0
    
           **long bpf_setsockopt(void ***_bpf_socket_**, int** _level_**, int** _optname_**, void**
           *****_optval_**, int** _optlen_**)**
    
                  **Description**
                         Emulate a call to **setsockopt()** on the socket
                         associated to _bpf_socket_ , which must be a full
                         socket. The _level_ at which the option resides and
                         the name _optname_ of the option must be specified,
                         see setsockopt(2) for more information.  The option
                         value of length _optlen_ is pointed by _optval_.
    
                         _bpf_socket_ should be one of the following:
    
                         • **struct bpf_sock_ops** for **BPF_PROG_TYPE_SOCK_OPS**.
    
                         • **struct bpf_sock_addr** for **BPF_CGROUP_INET4_CONNECT** ,
                           **BPF_CGROUP_INET6_CONNECT** and
                           **BPF_CGROUP_UNIX_CONNECT**.
    
                         This helper actually implements a subset of
                         **setsockopt()**.  It supports the following _level_ s:
    
                         • **SOL_SOCKET** , which supports the following _optname_ s:
                           **SO_RCVBUF** , **SO_SNDBUF** , **SO_MAX_PACING_RATE** ,
                           **SO_PRIORITY** , **SO_RCVLOWAT** , **SO_MARK** ,
                           **SO_BINDTODEVICE** , **SO_KEEPALIVE** , **SO_REUSEADDR** ,
                           **SO_REUSEPORT** , **SO_BINDTOIFINDEX** , **SO_TXREHASH**.
    
                         • **IPPROTO_TCP** , which supports the following
                           _optname_ s: **TCP_CONGESTION** , **TCP_BPF_IW** ,
                           **TCP_BPF_SNDCWND_CLAMP** , **TCP_SAVE_SYN** , **TCP_KEEPIDLE** ,
                           **TCP_KEEPINTVL** , **TCP_KEEPCNT** , **TCP_SYNCNT** ,
                           **TCP_USER_TIMEOUT** , **TCP_NOTSENT_LOWAT** , **TCP_NODELAY** ,
                           **TCP_MAXSEG** , **TCP_WINDOW_CLAMP** ,
                           **TCP_THIN_LINEAR_TIMEOUTS** , **TCP_BPF_DELACK_MAX** ,
                           **TCP_BPF_RTO_MIN** , **TCP_BPF_SOCK_OPS_CB_FLAGS**.
    
                         • **IPPROTO_IP** , which supports _optname_ **IP_TOS**.
    
                         • **IPPROTO_IPV6** , which supports the following
                           _optname_ s: **IPV6_TCLASS** , **IPV6_AUTOFLOWLABEL**.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_adjust_room(struct sk_buff ***_skb_**, s32** _len_diff_**, u32**
           _mode_**, u64** _flags_**)**
    
                  **Description**
                         Grow or shrink the room for data in the packet
                         associated to _skb_ by _len_diff_ , and according to the
                         selected _mode_.
    
                         By default, the helper will reset any offloaded
                         checksum indicator of the skb to CHECKSUM_NONE. This
                         can be avoided by the following flag:
    
                         • **BPF_F_ADJ_ROOM_NO_CSUM_RESET** : Do not reset
                           offloaded checksum data of the skb to
                           CHECKSUM_NONE.
    
                         There are two supported modes at this time:
    
                         • **BPF_ADJ_ROOM_MAC** : Adjust room at the mac layer
                           (room space is added or removed between the layer
                           2 and layer 3 headers).
    
                         • **BPF_ADJ_ROOM_NET** : Adjust room at the network layer
                           (room space is added or removed between the layer
                           3 and layer 4 headers).
    
                         The following flags are supported at this time:
    
                         • **BPF_F_ADJ_ROOM_FIXED_GSO** : Do not adjust gso_size.
                           Adjusting mss in this way is not allowed for
                           datagrams.
    
                         • **BPF_F_ADJ_ROOM_ENCAP_L3_IPV4** ,
                           **BPF_F_ADJ_ROOM_ENCAP_L3_IPV6** : Any new space is
                           reserved to hold a tunnel header.  Configure skb
                           offsets and other fields accordingly.
    
                         • **BPF_F_ADJ_ROOM_ENCAP_L4_GRE** ,
                           **BPF_F_ADJ_ROOM_ENCAP_L4_UDP** : Use with ENCAP_L3
                           flags to further specify the tunnel type.
    
                         • **BPF_F_ADJ_ROOM_ENCAP_L2**(_len_): Use with ENCAP_L3/L4
                           flags to further specify the tunnel type; _len_ is
                           the length of the inner MAC header.
    
                         • **BPF_F_ADJ_ROOM_ENCAP_L2_ETH** : Use with
                           BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify
                           the L2 type as Ethernet.
    
                         • **BPF_F_ADJ_ROOM_DECAP_L3_IPV4** ,
                           **BPF_F_ADJ_ROOM_DECAP_L3_IPV6** : Indicate the new IP
                           header version after decapsulating the outer IP
                           header. Used when the inner and outer IP versions
                           are different.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_redirect_map(struct bpf_map ***_map_**, u64** _key_**, u64** _flags_**)**
    
                  **Description**
                         Redirect the packet to the endpoint referenced by
                         _map_ at index _key_. Depending on its type, this _map_
                         can contain references to net devices (for
                         forwarding packets through other ports), or to CPUs
                         (for redirecting XDP frames to another CPU; but this
                         is only implemented for native XDP (with driver
                         support) as of this writing).
    
                         The lower two bits of _flags_ are used as the return
                         code if the map lookup fails. This is so that the
                         return value can be one of the XDP program return
                         codes up to **XDP_TX** , as chosen by the caller. The
                         higher bits of _flags_ can be set to BPF_F_BROADCAST
                         or BPF_F_EXCLUDE_INGRESS as defined below.
    
                         With BPF_F_BROADCAST the packet will be broadcasted
                         to all the interfaces in the map, with
                         BPF_F_EXCLUDE_INGRESS the ingress interface will be
                         excluded when do broadcasting.
    
                         See also **bpf_redirect**(), which only supports
                         redirecting to an ifindex, but doesn't require a map
                         to do so.
    
                  **Return XDP_REDIRECT** on success, or the value of the two
                         lower bits of the _flags_ argument on error.
    
           **long bpf_sk_redirect_map(struct sk_buff ***_skb_**, struct bpf_map ***_map_**,**
           **u32** _key_**, u64** _flags_**)**
    
                  **Description**
                         Redirect the packet to the socket referenced by _map_
                         (of type **BPF_MAP_TYPE_SOCKMAP**) at index _key_. Both
                         ingress and egress interfaces can be used for
                         redirection. The **BPF_F_INGRESS** value in _flags_ is
                         used to make the distinction (ingress path is
                         selected if the flag is present, egress path
                         otherwise). This is the only flag supported for now.
    
                  **Return SK_PASS** on success, or **SK_DROP** on error.
    
           **long bpf_sock_map_update(struct bpf_sock_ops ***_skops_**, struct**
           **bpf_map ***_map_**, void ***_key_**, u64** _flags_**)**
    
                  **Description**
                         Add an entry to, or update a _map_ referencing
                         sockets. The _skops_ is used as a new value for the
                         entry associated to _key_. _flags_ is one of:
    
                         **BPF_NOEXIST**
                                The entry for _key_ must not exist in the map.
    
                         **BPF_EXIST**
                                The entry for _key_ must already exist in the
                                map.
    
                         **BPF_ANY**
                                No condition on the existence of the entry
                                for _key_.
    
                         If the _map_ has eBPF programs (parser and verdict),
                         those will be inherited by the socket being added.
                         If the socket is already attached to eBPF programs,
                         this results in an error.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_xdp_adjust_meta(struct xdp_buff ***_xdp_md_**, int** _delta_**)**
    
                  **Description**
                         Adjust the address pointed by _xdp_md_**- >data_meta **by
                         _delta_ (which can be positive or negative). Note that
                         this operation modifies the address stored in
                         _xdp_md_**- >data**, so the latter must be loaded only
                         after the helper has been called.
    
                         The use of _xdp_md_**- >data_meta **is optional and
                         programs are not required to use it. The rationale
                         is that when the packet is processed with XDP (e.g.
                         as DoS filter), it is possible to push further meta
                         data along with it before passing to the stack, and
                         to give the guarantee that an ingress eBPF program
                         attached as a TC classifier on the same device can
                         pick this up for further post-processing. Since TC
                         works with socket buffers, it remains possible to
                         set from XDP the **mark** or **priority** pointers, or other
                         pointers for the socket buffer.  Having this scratch
                         space generic and programmable allows for more
                         flexibility as the user is free to store whatever
                         meta data they need.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_perf_event_read_value(struct bpf_map ***_map_**, u64** _flags_**,**
           **struct bpf_perf_event_value ***_buf_**, u32** _buf_size_**)**
    
                  **Description**
                         Read the value of a perf event counter, and store it
                         into _buf_ of size _buf_size_. This helper relies on a
                         _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The
                         nature of the perf event counter is selected when
                         _map_ is updated with perf event file descriptors. The
                         _map_ is an array whose size is the number of
                         available CPUs, and each cell contains a value
                         relative to one CPU. The value to retrieve is
                         indicated by _flags_ , that contains the index of the
                         CPU to look up, masked with **BPF_F_INDEX_MASK**.
                         Alternatively, _flags_ can be set to **BPF_F_CURRENT_CPU**
                         to indicate that the value for the current CPU
                         should be retrieved.
    
                         This helper behaves in a way close to
                         **bpf_perf_event_read**() helper, save that instead of
                         just returning the value observed, it fills the _buf_
                         structure. This allows for additional data to be
                         retrieved: in particular, the enabled and running
                         times (in _buf_**- >enabled **and _buf_**- >running**,
                         respectively) are copied. In general,
                         **bpf_perf_event_read_value**() is recommended over
                         **bpf_perf_event_read**(), which has some ABI issues and
                         provides fewer functionalities.
    
                         These values are interesting, because hardware PMU
                         (Performance Monitoring Unit) counters are limited
                         resources. When there are more PMU based perf events
                         opened than available counters, kernel will
                         multiplex these events so each event gets certain
                         percentage (but not all) of the PMU time. In case
                         that multiplexing happens, the number of samples or
                         counter value will not reflect the case compared to
                         when no multiplexing occurs. This makes comparison
                         between different runs difficult.  Typically, the
                         counter value should be normalized before comparing
                         to other experiments. The usual normalization is
                         done as follows.
    
                            normalized_counter = counter * t_enabled / t_running
    
                         Where t_enabled is the time enabled for event and
                         t_running is the time running for event since last
                         normalization. The enabled and running times are
                         accumulated since the perf event open. To achieve
                         scaling factor between two invocations of an eBPF
                         program, users can use CPU id as the key (which is
                         typical for perf array usage model) to remember the
                         previous value and do the calculation inside the
                         eBPF program.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_perf_prog_read_value(struct bpf_perf_event_data ***_ctx_**,**
           **struct bpf_perf_event_value ***_buf_**, u32** _buf_size_**)**
    
                  **Description**
                         For an eBPF program attached to a perf event,
                         retrieve the value of the event counter associated
                         to _ctx_ and store it in the structure pointed by _buf_
                         and of size _buf_size_. Enabled and running times are
                         also stored in the structure (see description of
                         helper **bpf_perf_event_read_value**() for more
                         details).
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_getsockopt(void ***_bpf_socket_**, int** _level_**, int** _optname_**, void**
           *****_optval_**, int** _optlen_**)**
    
                  **Description**
                         Emulate a call to **getsockopt()** on the socket
                         associated to _bpf_socket_ , which must be a full
                         socket. The _level_ at which the option resides and
                         the name _optname_ of the option must be specified,
                         see getsockopt(2) for more information.  The
                         retrieved value is stored in the structure pointed
                         by _opval_ and of length _optlen_.
    
                         _bpf_socket_ should be one of the following:
    
                         • **struct bpf_sock_ops** for **BPF_PROG_TYPE_SOCK_OPS**.
    
                         • **struct bpf_sock_addr** for **BPF_CGROUP_INET4_CONNECT** ,
                           **BPF_CGROUP_INET6_CONNECT** and
                           **BPF_CGROUP_UNIX_CONNECT**.
    
                         This helper actually implements a subset of
                         **getsockopt()**.  It supports the same set of _optname_ s
                         that is supported by the **bpf_setsockopt**() helper.
                         The exceptions are **TCP_BPF_*** is **bpf_setsockopt**()
                         only and **TCP_SAVED_SYN** is **bpf_getsockopt**() only.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_override_return(struct pt_regs ***_regs_**, u64** _rc_**)**
    
                  **Description**
                         Used for error injection, this helper uses kprobes
                         to override the return value of the probed function,
                         and to set it to _rc_.  The first argument is the
                         context _regs_ on which the kprobe works.
    
                         This helper works by setting the PC (program
                         counter) to an override function which is run in
                         place of the original probed function. This means
                         the probed function is not run at all. The
                         replacement function just returns with the required
                         value.
    
                         This helper has security implications, and thus is
                         subject to restrictions. It is only available if the
                         kernel was compiled with the
                         **CONFIG_BPF_KPROBE_OVERRIDE** configuration option, and
                         in this case it only works on functions tagged with
                         **ALLOW_ERROR_INJECTION** in the kernel code.
    
                  **Return** 0
    
           **long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops ***_bpf_sock_**, int**
           _argval_**)**
    
                  **Description**
                         Attempt to set the value of the
                         **bpf_sock_ops_cb_flags** field for the full TCP socket
                         associated to _bpf_sock_ops_ to _argval_.
    
                         The primary use of this field is to determine if
                         there should be calls to eBPF programs of type
                         **BPF_PROG_TYPE_SOCK_OPS** at various points in the TCP
                         code. A program of the same type can change its
                         value, per connection and as necessary, when the
                         connection is established. This field is directly
                         accessible for reading, but this helper must be used
                         for updates in order to return an error if an eBPF
                         program tries to set a callback that is not
                         supported in the current kernel.
    
                         _argval_ is a flag array which can combine these
                         flags:
    
                         • **BPF_SOCK_OPS_RTO_CB_FLAG**(retransmission time out)
    
                         • **BPF_SOCK_OPS_RETRANS_CB_FLAG**(retransmission)
    
                         • **BPF_SOCK_OPS_STATE_CB_FLAG**(TCP state change)
    
                         • **BPF_SOCK_OPS_RTT_CB_FLAG**(every RTT)
    
                         Therefore, this function can be used to clear a
                         callback flag by setting the appropriate bit to
                         zero. e.g. to disable the RTO callback:
    
                         **bpf_sock_ops_cb_flags_set(bpf_sock,**
                                **bpf_sock- >bpf_sock_ops_cb_flags &**
                                **~BPF_SOCK_OPS_RTO_CB_FLAG)**
    
                         Here are some examples of where one could call such
                         eBPF program:
    
                         • When RTO fires.
    
                         • When a packet is retransmitted.
    
                         • When the connection terminates.
    
                         • When a packet is sent.
    
                         • When a packet is received.
    
                  **Return** Code **-EINVAL** if the socket is not a full TCP socket;
                         otherwise, a positive number containing the bits
                         that could not be set is returned (which comes down
                         to 0 if all bits were set as required).
    
           **long bpf_msg_redirect_map(struct sk_msg_buff ***_msg_**, struct bpf_map**
           *****_map_**, u32** _key_**, u64** _flags_**)**
    
                  **Description**
                         This helper is used in programs implementing
                         policies at the socket level. If the message _msg_ is
                         allowed to pass (i.e. if the verdict eBPF program
                         returns **SK_PASS**), redirect it to the socket
                         referenced by _map_ (of type **BPF_MAP_TYPE_SOCKMAP**) at
                         index _key_. Both ingress and egress interfaces can be
                         used for redirection. The **BPF_F_INGRESS** value in
                         _flags_ is used to make the distinction (ingress path
                         is selected if the flag is present, egress path
                         otherwise). This is the only flag supported for now.
    
                  **Return SK_PASS** on success, or **SK_DROP** on error.
    
           **long bpf_msg_apply_bytes(struct sk_msg_buff ***_msg_**, u32** _bytes_**)**
    
                  **Description**
                         For socket policies, apply the verdict of the eBPF
                         program to the next _bytes_ (number of bytes) of
                         message _msg_.
    
                         For example, this helper can be used in the
                         following cases:
    
                         • A single **sendmsg**() or **sendfile**() system call
                           contains multiple logical messages that the eBPF
                           program is supposed to read and for which it
                           should apply a verdict.
    
                         • An eBPF program only cares to read the first _bytes_
                           of a _msg_. If the message has a large payload, then
                           setting up and calling the eBPF program repeatedly
                           for all bytes, even though the verdict is already
                           known, would create unnecessary overhead.
    
                         When called from within an eBPF program, the helper
                         sets a counter internal to the BPF infrastructure,
                         that is used to apply the last verdict to the next
                         _bytes_. If _bytes_ is smaller than the current data
                         being processed from a **sendmsg**() or **sendfile**()
                         system call, the first _bytes_ will be sent and the
                         eBPF program will be re-run with the pointer for
                         start of data pointing to byte number _bytes_ **+ 1**. If
                         _bytes_ is larger than the current data being
                         processed, then the eBPF verdict will be applied to
                         multiple **sendmsg**() or **sendfile**() calls until _bytes_
                         are consumed.
    
                         Note that if a socket closes with the internal
                         counter holding a non-zero value, this is not a
                         problem because data is not being buffered for _bytes_
                         and is sent as it is received.
    
                  **Return** 0
    
           **long bpf_msg_cork_bytes(struct sk_msg_buff ***_msg_**, u32** _bytes_**)**
    
                  **Description**
                         For socket policies, prevent the execution of the
                         verdict eBPF program for message _msg_ until _bytes_
                         (byte number) have been accumulated.
    
                         This can be used when one needs a specific number of
                         bytes before a verdict can be assigned, even if the
                         data spans multiple **sendmsg**() or **sendfile**() calls.
                         The extreme case would be a user calling **sendmsg**()
                         repeatedly with 1-byte long message segments.
                         Obviously, this is bad for performance, but it is
                         still valid. If the eBPF program needs _bytes_ bytes
                         to validate a header, this helper can be used to
                         prevent the eBPF program to be called again until
                         _bytes_ have been accumulated.
    
                  **Return** 0
    
           **long bpf_msg_pull_data(struct sk_msg_buff ***_msg_**, u32** _start_**, u32**
           _end_**, u64** _flags_**)**
    
                  **Description**
                         For socket policies, pull in non-linear data from
                         user space for _msg_ and set pointers _msg_**- >data **and
                         _msg_**- >data_end **to _start_ and _end_ bytes offsets into
                         _msg_ , respectively.
    
                         If a program of type **BPF_PROG_TYPE_SK_MSG** is run on
                         a _msg_ it can only parse data that the (**data** ,
                         **data_end**) pointers have already consumed. For
                         **sendmsg**() hooks this is likely the first scatterlist
                         element. But for calls relying on the **sendpage**
                         handler (e.g. **sendfile**()) this will be the range (**0** ,
                         **0**) because the data is shared with user space and by
                         default the objective is to avoid allowing user
                         space to modify data while (or after) eBPF verdict
                         is being decided. This helper can be used to pull in
                         data and to set the start and end pointer to given
                         values. Data will be copied if necessary (i.e. if
                         data was not linear and if start and end pointers do
                         not point to the same chunk).
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_bind(struct bpf_sock_addr ***_ctx_**, struct sockaddr ***_addr_**,**
           **int** _addr_len_**)**
    
                  **Description**
                         Bind the socket associated to _ctx_ to the address
                         pointed by _addr_ , of length _addr_len_. This allows for
                         making outgoing connection from the desired IP
                         address, which can be useful for example when all
                         processes inside a cgroup should use one single IP
                         address on a host that has multiple IP configured.
    
                         This helper works for IPv4 and IPv6, TCP and UDP
                         sockets. The domain (_addr_**- >sa_family**) must be
                         **AF_INET**(or **AF_INET6**). It's advised to pass zero
                         port (**sin_port** or **sin6_port**) which triggers
                         IP_BIND_ADDRESS_NO_PORT-like behavior and lets the
                         kernel efficiently pick up an unused port as long as
                         4-tuple is unique. Passing non-zero port might lead
                         to degraded performance.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_xdp_adjust_tail(struct xdp_buff ***_xdp_md_**, int** _delta_**)**
    
                  **Description**
                         Adjust (move) _xdp_md_**- >data_end **by _delta_ bytes. It is
                         possible to both shrink and grow the packet tail.
                         Shrink done via _delta_ being a negative integer.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_get_xfrm_state(struct sk_buff ***_skb_**, u32** _index_**, struct**
           **bpf_xfrm_state ***_xfrm_state_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         Retrieve the XFRM state (IP transform framework, see
                         also ip-xfrm(8)) at _index_ in XFRM "security path"
                         for _skb_.
    
                         The retrieved value is stored in the **struct**
                         **bpf_xfrm_state** pointed by _xfrm_state_ and of length
                         _size_.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                         This helper is available only if the kernel was
                         compiled with **CONFIG_XFRM** configuration option.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_get_stack(void ***_ctx_**, void ***_buf_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         Return a user or a kernel stack in bpf program
                         provided buffer.  To achieve this, the helper needs
                         _ctx_ , which is a pointer to the context on which the
                         tracing program is executed.  To store the
                         stacktrace, the bpf program provides _buf_ with a
                         nonnegative _size_.
    
                         The last argument, _flags_ , holds the number of stack
                         frames to skip (from 0 to 255), masked with
                         **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to
                         set the following flags:
    
                         **BPF_F_USER_STACK**
                                Collect a user space stack instead of a
                                kernel stack.
    
                         **BPF_F_USER_BUILD_ID**
                                Collect (build_id, file_offset) instead of
                                ips for user stack, only valid if
                                **BPF_F_USER_STACK** is also specified.
    
                                _file_offset_ is an offset relative to the
                                beginning of the executable or shared object
                                file backing the vma which the _ip_ falls in.
                                It is _not_ an offset relative to that object's
                                base address. Accordingly, it must be
                                adjusted by adding (sh_addr - sh_offset),
                                where sh_{addr,offset} correspond to the
                                executable section containing _file_offset_ in
                                the object, for comparisons to symbols'
                                st_value to be valid.
    
                         **bpf_get_stack**() can collect up to
                         **PERF_MAX_STACK_DEPTH** both kernel and user frames,
                         subject to sufficient large buffer size. Note that
                         this limit can be controlled with the **sysctl**
                         program, and that it should be manually increased in
                         order to profile long user stacks (such as stacks
                         for Java programs). To do so, use:
    
                            # sysctl kernel.perf_event_max_stack=<new value>
    
                  **Return** The non-negative copied _buf_ length equal to or less
                         than _size_ on success, or a negative error in case of
                         failure.
    
           **long bpf_skb_load_bytes_relative(const void ***_skb_**, u32** _offset_**, void**
           *****_to_**, u32** _len_**, u32** _start_header_**)**
    
                  **Description**
                         This helper is similar to **bpf_skb_load_bytes**() in
                         that it provides an easy way to load _len_ bytes from
                         _offset_ from the packet associated to _skb_ , into the
                         buffer pointed by _to_. The difference to
                         **bpf_skb_load_bytes**() is that a fifth argument
                         _start_header_ exists in order to select a base offset
                         to start from. _start_header_ can be one of:
    
                         **BPF_HDR_START_MAC**
                                Base offset to load data from is _skb_ 's mac
                                header.
    
                         **BPF_HDR_START_NET**
                                Base offset to load data from is _skb_ 's
                                network header.
    
                         In general, "direct packet access" is the preferred
                         method to access packet data, however, this helper
                         is in particular useful in socket filters where
                         _skb_**- >data **does not always point to the start of the
                         mac header and where "direct packet access" is not
                         available.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_fib_lookup(void ***_ctx_**, struct bpf_fib_lookup ***_params_**, int**
           _plen_**, u32** _flags_**)**
    
                  **Description**
                         Do FIB lookup in kernel tables using parameters in
                         _params_.  If lookup is successful and result shows
                         packet is to be forwarded, the neighbor tables are
                         searched for the nexthop.  If successful (ie., FIB
                         lookup shows forwarding and nexthop is resolved),
                         the nexthop address is returned in ipv4_dst or
                         ipv6_dst based on family, smac is set to mac address
                         of egress device, dmac is set to nexthop mac
                         address, rt_metric is set to metric from route
                         (IPv4/IPv6 only), and ifindex is set to the device
                         index of the nexthop from the FIB lookup.
    
                         _plen_ argument is the size of the passed in struct.
                         _flags_ argument can be a combination of one or more
                         of the following values:
    
                         **BPF_FIB_LOOKUP_DIRECT**
                                Do a direct table lookup vs full lookup using
                                FIB rules.
    
                         **BPF_FIB_LOOKUP_TBID**
                                Used with BPF_FIB_LOOKUP_DIRECT.  Use the
                                routing table ID present in _params_ ->tbid for
                                the fib lookup.
    
                         **BPF_FIB_LOOKUP_OUTPUT**
                                Perform lookup from an egress perspective
                                (default is ingress).
    
                         **BPF_FIB_LOOKUP_SKIP_NEIGH**
                                Skip the neighbour table lookup. _params_ ->dmac
                                and _params_ ->smac will not be set as output. A
                                common use case is to call
                                **bpf_redirect_neigh**() after doing
                                **bpf_fib_lookup**().
    
                         **BPF_FIB_LOOKUP_SRC**
                                Derive and set source IP addr in
                                _params_ ->ipv{4,6}_src for the nexthop. If the
                                src addr cannot be derived,
                                **BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned. In
                                this case, _params_ ->dmac and _params_ ->smac are
                                not set either.
    
                         **BPF_FIB_LOOKUP_MARK**
                                Use the mark present in _params_ ->mark for the
                                fib lookup.  This option should not be used
                                with BPF_FIB_LOOKUP_DIRECT, as it only has
                                meaning for full lookups.
    
                         _ctx_ is either **struct xdp_md** for XDP programs or
                         **struct sk_buff** tc cls_act programs.
    
                  **Return**
    
                         • < 0 if any input argument is invalid
    
                         • 0 on success (packet is forwarded, nexthop
                           neighbor exists)
    
                         • > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why
                           the packet is not forwarded or needs assist from
                           full stack
    
                         If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED,
                         then the MTU was exceeded and output
                         params->mtu_result contains the MTU.
    
           **long bpf_sock_hash_update(struct bpf_sock_ops ***_skops_**, struct**
           **bpf_map ***_map_**, void ***_key_**, u64** _flags_**)**
    
                  **Description**
                         Add an entry to, or update a sockhash _map_
                         referencing sockets.  The _skops_ is used as a new
                         value for the entry associated to _key_. _flags_ is one
                         of:
    
                         **BPF_NOEXIST**
                                The entry for _key_ must not exist in the map.
    
                         **BPF_EXIST**
                                The entry for _key_ must already exist in the
                                map.
    
                         **BPF_ANY**
                                No condition on the existence of the entry
                                for _key_.
    
                         If the _map_ has eBPF programs (parser and verdict),
                         those will be inherited by the socket being added.
                         If the socket is already attached to eBPF programs,
                         this results in an error.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_msg_redirect_hash(struct sk_msg_buff ***_msg_**, struct bpf_map**
           *****_map_**, void ***_key_**, u64** _flags_**)**
    
                  **Description**
                         This helper is used in programs implementing
                         policies at the socket level. If the message _msg_ is
                         allowed to pass (i.e. if the verdict eBPF program
                         returns **SK_PASS**), redirect it to the socket
                         referenced by _map_ (of type **BPF_MAP_TYPE_SOCKHASH**)
                         using hash _key_. Both ingress and egress interfaces
                         can be used for redirection. The **BPF_F_INGRESS** value
                         in _flags_ is used to make the distinction (ingress
                         path is selected if the flag is present, egress path
                         otherwise). This is the only flag supported for now.
    
                  **Return SK_PASS** on success, or **SK_DROP** on error.
    
           **long bpf_sk_redirect_hash(struct sk_buff ***_skb_**, struct bpf_map**
           *****_map_**, void ***_key_**, u64** _flags_**)**
    
                  **Description**
                         This helper is used in programs implementing
                         policies at the skb socket level. If the sk_buff _skb_
                         is allowed to pass (i.e.  if the verdict eBPF
                         program returns **SK_PASS**), redirect it to the socket
                         referenced by _map_ (of type **BPF_MAP_TYPE_SOCKHASH**)
                         using hash _key_. Both ingress and egress interfaces
                         can be used for redirection. The **BPF_F_INGRESS** value
                         in _flags_ is used to make the distinction (ingress
                         path is selected if the flag is present, egress
                         otherwise). This is the only flag supported for now.
    
                  **Return SK_PASS** on success, or **SK_DROP** on error.
    
           **long bpf_lwt_push_encap(struct sk_buff ***_skb_**, u32** _type_**, void ***_hdr_**,**
           **u32** _len_**)**
    
                  **Description**
                         Encapsulate the packet associated to _skb_ within a
                         Layer 3 protocol header. This header is provided in
                         the buffer at address _hdr_ , with _len_ its size in
                         bytes. _type_ indicates the protocol of the header and
                         can be one of:
    
                         **BPF_LWT_ENCAP_SEG6**
                                IPv6 encapsulation with Segment Routing
                                Header (**struct ipv6_sr_hdr**). _hdr_ only
                                contains the SRH, the IPv6 header is computed
                                by the kernel.
    
                         **BPF_LWT_ENCAP_SEG6_INLINE**
                                Only works if _skb_ contains an IPv6 packet.
                                Insert a Segment Routing Header (**struct**
                                **ipv6_sr_hdr**) inside the IPv6 header.
    
                         **BPF_LWT_ENCAP_IP**
                                IP encapsulation (GRE/GUE/IPIP/etc). The
                                outer header must be IPv4 or IPv6, followed
                                by zero or more additional headers, up to
                                **LWT_BPF_MAX_HEADROOM** total bytes in all
                                prepended headers. Please note that if
                                **skb_is_gso**(_skb_) is true, no more than two
                                headers can be prepended, and the inner
                                header, if present, should be either GRE or
                                UDP/GUE.
    
                         **BPF_LWT_ENCAP_SEG6** * types can be called by BPF
                         programs of type **BPF_PROG_TYPE_LWT_IN** ;
                         **BPF_LWT_ENCAP_IP** type can be called by bpf programs
                         of types **BPF_PROG_TYPE_LWT_IN** and
                         **BPF_PROG_TYPE_LWT_XMIT**.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_lwt_seg6_store_bytes(struct sk_buff ***_skb_**, u32** _offset_**,**
           **const void ***_from_**, u32** _len_**)**
    
                  **Description**
                         Store _len_ bytes from address _from_ into the packet
                         associated to _skb_ , at _offset_. Only the flags, tag
                         and TLVs inside the outermost IPv6 Segment Routing
                         Header can be modified through this helper.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_lwt_seg6_adjust_srh(struct sk_buff ***_skb_**, u32** _offset_**, s32**
           _delta_**)**
    
                  **Description**
                         Adjust the size allocated to TLVs in the outermost
                         IPv6 Segment Routing Header contained in the packet
                         associated to _skb_ , at position _offset_ by _delta_
                         bytes. Only offsets after the segments are accepted.
                         _delta_ can be as well positive (growing) as negative
                         (shrinking).
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_lwt_seg6_action(struct sk_buff ***_skb_**, u32** _action_**, void**
           *****_param_**, u32** _param_len_**)**
    
                  **Description**
                         Apply an IPv6 Segment Routing action of type _action_
                         to the packet associated to _skb_. Each action takes a
                         parameter contained at address _param_ , and of length
                         _param_len_ bytes.  _action_ can be one of:
    
                         **SEG6_LOCAL_ACTION_END_X**
                                End.X action: Endpoint with Layer-3
                                cross-connect.  Type of _param_ : **struct**
                                **in6_addr**.
    
                         **SEG6_LOCAL_ACTION_END_T**
                                End.T action: Endpoint with specific IPv6
                                table lookup.  Type of _param_ : **int**.
    
                         **SEG6_LOCAL_ACTION_END_B6**
                                End.B6 action: Endpoint bound to an SRv6
                                policy.  Type of _param_ : **struct ipv6_sr_hdr**.
    
                         **SEG6_LOCAL_ACTION_END_B6_ENCAP**
                                End.B6.Encap action: Endpoint bound to an
                                SRv6 encapsulation policy.  Type of _param_ :
                                **struct ipv6_sr_hdr**.
    
                         A call to this helper is susceptible to change the
                         underlying packet buffer. Therefore, at load time,
                         all checks on pointers previously done by the
                         verifier are invalidated and must be performed
                         again, if the helper is used in combination with
                         direct packet access.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_rc_repeat(void ***_ctx_**)**
    
                  **Description**
                         This helper is used in programs implementing IR
                         decoding, to report a successfully decoded repeat
                         key message. This delays the generation of a key up
                         event for previously generated key down event.
    
                         Some IR protocols like NEC have a special IR message
                         for repeating last button, for when a button is held
                         down.
    
                         The _ctx_ should point to the lirc sample as passed
                         into the program.
    
                         This helper is only available is the kernel was
                         compiled with the **CONFIG_BPF_LIRC_MODE2**
                         configuration option set to "**y** ".
    
                  **Return** 0
    
           **long bpf_rc_keydown(void ***_ctx_**, u32** _protocol_**, u64** _scancode_**, u32**
           _toggle_**)**
    
                  **Description**
                         This helper is used in programs implementing IR
                         decoding, to report a successfully decoded key press
                         with _scancode_ , _toggle_ value in the given _protocol_.
                         The scancode will be translated to a keycode using
                         the rc keymap, and reported as an input key down
                         event. After a period a key up event is generated.
                         This period can be extended by calling either
                         **bpf_rc_keydown**() again with the same values, or
                         calling **bpf_rc_repeat**().
    
                         Some protocols include a toggle bit, in case the
                         button was released and pressed again between
                         consecutive scancodes.
    
                         The _ctx_ should point to the lirc sample as passed
                         into the program.
    
                         The _protocol_ is the decoded protocol number (see
                         **enum rc_proto** for some predefined values).
    
                         This helper is only available is the kernel was
                         compiled with the **CONFIG_BPF_LIRC_MODE2**
                         configuration option set to "**y** ".
    
                  **Return** 0
    
           **u64 bpf_skb_cgroup_id(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Return the cgroup v2 id of the socket associated
                         with the _skb_.  This is roughly similar to the
                         **bpf_get_cgroup_classid**() helper for cgroup v1 by
                         providing a tag resp. identifier that can be matched
                         on or used for map lookups e.g. to implement policy.
                         The cgroup v2 id of a given path in the hierarchy is
                         exposed in user space through the f_handle API in
                         order to get to the same 64-bit id.
    
                         This helper can be used on TC egress path, but not
                         on ingress, and is available only if the kernel was
                         compiled with the **CONFIG_SOCK_CGROUP_DATA**
                         configuration option.
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **u64 bpf_get_current_cgroup_id(void)**
    
                  **Description**
                         Get the current cgroup id based on the cgroup within
                         which the current task is running.
    
                  **Return** A 64-bit integer containing the current cgroup id
                         based on the cgroup within which the current task is
                         running.
    
           **void *bpf_get_local_storage(void ***_map_**, u64** _flags_**)**
    
                  **Description**
                         Get the pointer to the local storage area.  The type
                         and the size of the local storage is defined by the
                         _map_ argument.  The _flags_ meaning is specific for
                         each map type, and has to be 0 for cgroup local
                         storage.
    
                         Depending on the BPF program type, a local storage
                         area can be shared between multiple instances of the
                         BPF program, running simultaneously.
    
                         A user should care about the synchronization by
                         himself.  For example, by using the **BPF_ATOMIC**
                         instructions to alter the shared data.
    
                  **Return** A pointer to the local storage area.
    
           **long bpf_sk_select_reuseport(struct sk_reuseport_md ***_reuse_**, struct**
           **bpf_map ***_map_**, void ***_key_**, u64** _flags_**)**
    
                  **Description**
                         Select a **SO_REUSEPORT** socket from a
                         **BPF_MAP_TYPE_REUSEPORT_SOCKARRAY** _map_.  It checks the
                         selected socket is matching the incoming request in
                         the socket buffer.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u64 bpf_skb_ancestor_cgroup_id(struct sk_buff ***_skb_**, int**
           _ancestor_level_**)**
    
                  **Description**
                         Return id of cgroup v2 that is ancestor of cgroup
                         associated with the _skb_ at the _ancestor_level_.  The
                         root cgroup is at _ancestor_level_ zero and each step
                         down the hierarchy increments the level. If
                         _ancestor_level_ == level of cgroup associated with
                         _skb_ , then return value will be same as that of
                         **bpf_skb_cgroup_id**().
    
                         The helper is useful to implement policies based on
                         cgroups that are upper in hierarchy than immediate
                         cgroup associated with _skb_.
    
                         The format of returned id and helper limitations are
                         same as in **bpf_skb_cgroup_id**().
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **struct bpf_sock *bpf_sk_lookup_tcp(void ***_ctx_**, struct**
           **bpf_sock_tuple ***_tuple_**, u32** _tuple_size_**, u64** _netns_**, u64** _flags_**)**
    
                  **Description**
                         Look for TCP socket matching _tuple_ , optionally in a
                         child network namespace _netns_. The return value must
                         be checked, and if non-**NULL** , released via
                         **bpf_sk_release**().
    
                         The _ctx_ should point to the context of the program,
                         such as the skb or socket (depending on the hook in
                         use). This is used to determine the base network
                         namespace for the lookup.
    
                         _tuple_size_ must be one of:
    
                         **sizeof(**_tuple_**- >ipv4)**
                                Look for an IPv4 socket.
    
                         **sizeof(**_tuple_**- >ipv6)**
                                Look for an IPv6 socket.
    
                         If the _netns_ is a negative signed 32-bit integer,
                         then the socket lookup table in the netns associated
                         with the _ctx_ will be used. For the TC hooks, this is
                         the netns of the device in the skb. For socket
                         hooks, this is the netns of the socket.  If _netns_ is
                         any other signed 32-bit value greater than or equal
                         to zero then it specifies the ID of the netns
                         relative to the netns associated with the _ctx_. _netns_
                         values beyond the range of 32-bit integers are
                         reserved for future use.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                         This helper is available only if the kernel was
                         compiled with **CONFIG_NET** configuration option.
    
                  **Return** Pointer to **struct bpf_sock** , or **NULL** in case of
                         failure.  For sockets with reuseport option, the
                         **struct bpf_sock** result is from _reuse_**- >socks**[] using
                         the hash of the tuple.
    
           **struct bpf_sock *bpf_sk_lookup_udp(void ***_ctx_**, struct**
           **bpf_sock_tuple ***_tuple_**, u32** _tuple_size_**, u64** _netns_**, u64** _flags_**)**
    
                  **Description**
                         Look for UDP socket matching _tuple_ , optionally in a
                         child network namespace _netns_. The return value must
                         be checked, and if non-**NULL** , released via
                         **bpf_sk_release**().
    
                         The _ctx_ should point to the context of the program,
                         such as the skb or socket (depending on the hook in
                         use). This is used to determine the base network
                         namespace for the lookup.
    
                         _tuple_size_ must be one of:
    
                         **sizeof(**_tuple_**- >ipv4)**
                                Look for an IPv4 socket.
    
                         **sizeof(**_tuple_**- >ipv6)**
                                Look for an IPv6 socket.
    
                         If the _netns_ is a negative signed 32-bit integer,
                         then the socket lookup table in the netns associated
                         with the _ctx_ will be used. For the TC hooks, this is
                         the netns of the device in the skb. For socket
                         hooks, this is the netns of the socket.  If _netns_ is
                         any other signed 32-bit value greater than or equal
                         to zero then it specifies the ID of the netns
                         relative to the netns associated with the _ctx_. _netns_
                         values beyond the range of 32-bit integers are
                         reserved for future use.
    
                         All values for _flags_ are reserved for future usage,
                         and must be left at zero.
    
                         This helper is available only if the kernel was
                         compiled with **CONFIG_NET** configuration option.
    
                  **Return** Pointer to **struct bpf_sock** , or **NULL** in case of
                         failure.  For sockets with reuseport option, the
                         **struct bpf_sock** result is from _reuse_**- >socks**[] using
                         the hash of the tuple.
    
           **long bpf_sk_release(void ***_sock_**)**
    
                  **Description**
                         Release the reference held by _sock_. _sock_ must be a
                         non-**NULL** pointer that was returned from
                         **bpf_sk_lookup_xxx**().
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_map_push_elem(struct bpf_map ***_map_**, const void ***_value_**, u64**
           _flags_**)**
    
                  **Description**
                         Push an element _value_ in _map_. _flags_ is one of:
    
                         **BPF_EXIST**
                                If the queue/stack is full, the oldest
                                element is removed to make room for this.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_map_pop_elem(struct bpf_map ***_map_**, void ***_value_**)**
    
                  **Description**
                         Pop an element from _map_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_map_peek_elem(struct bpf_map ***_map_**, void ***_value_**)**
    
                  **Description**
                         Get an element from _map_ without removing it.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_msg_push_data(struct sk_msg_buff ***_msg_**, u32** _start_**, u32**
           _len_**, u64** _flags_**)**
    
                  **Description**
                         For socket policies, insert _len_ bytes into _msg_ at
                         offset _start_.
    
                         If a program of type **BPF_PROG_TYPE_SK_MSG** is run on
                         a _msg_ it may want to insert metadata or options into
                         the _msg_.  This can later be read and used by any of
                         the lower layer BPF hooks.
    
                         This helper may fail if under memory pressure (a
                         malloc fails) in these cases BPF programs will get
                         an appropriate error and BPF programs will need to
                         handle them.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_msg_pop_data(struct sk_msg_buff ***_msg_**, u32** _start_**, u32** _len_**,**
           **u64** _flags_**)**
    
                  **Description**
                         Will remove _len_ bytes from a _msg_ starting at byte
                         _start_.  This may result in **ENOMEM** errors under
                         certain situations if an allocation and copy are
                         required due to a full ring buffer.  However, the
                         helper will try to avoid doing the allocation if
                         possible. Other errors can occur if input parameters
                         are invalid either due to _start_ byte not being valid
                         part of _msg_ payload and/or _pop_ value being to large.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_rc_pointer_rel(void ***_ctx_**, s32** _rel_x_**, s32** _rel_y_**)**
    
                  **Description**
                         This helper is used in programs implementing IR
                         decoding, to report a successfully decoded pointer
                         movement.
    
                         The _ctx_ should point to the lirc sample as passed
                         into the program.
    
                         This helper is only available is the kernel was
                         compiled with the **CONFIG_BPF_LIRC_MODE2**
                         configuration option set to "**y** ".
    
                  **Return** 0
    
           **long bpf_spin_lock(struct bpf_spin_lock ***_lock_**)**
    
                  **Description**
                         Acquire a spinlock represented by the pointer _lock_ ,
                         which is stored as part of a value of a map. Taking
                         the lock allows to safely update the rest of the
                         fields in that value. The spinlock can (and must)
                         later be released with a call to
                         **bpf_spin_unlock**(_lock_).
    
                         Spinlocks in BPF programs come with a number of
                         restrictions and constraints:
    
                         • **bpf_spin_lock** objects are only allowed inside maps
                           of types **BPF_MAP_TYPE_HASH** and **BPF_MAP_TYPE_ARRAY**
                           (this list could be extended in the future).
    
                         • BTF description of the map is mandatory.
    
                         • The BPF program can take ONE lock at a time, since
                           taking two or more could cause dead locks.
    
                         • Only one **struct bpf_spin_lock** is allowed per map
                           element.
    
                         • When the lock is taken, calls (either BPF to BPF
                           or helpers) are not allowed.
    
                         • The **BPF_LD_ABS** and **BPF_LD_IND** instructions are not
                           allowed inside a spinlock-ed region.
    
                         • The BPF program MUST call **bpf_spin_unlock**() to
                           release the lock, on all execution paths, before
                           it returns.
    
                         • The BPF program can access **struct bpf_spin_lock**
                           only via the **bpf_spin_lock**() and **bpf_spin_unlock**()
                           helpers. Loading or storing data into the **struct**
                           **bpf_spin_lock** _lock_**;** field of a map is not allowed.
    
                         • To use the **bpf_spin_lock**() helper, the BTF
                           description of the map value must be a struct and
                           have **struct bpf_spin_lock** _anyname_**;** field at the
                           top level.  Nested lock inside another struct is
                           not allowed.
    
                         • The **struct bpf_spin_lock** _lock_ field in a map value
                           must be aligned on a multiple of 4 bytes in that
                           value.
    
                         • Syscall with command **BPF_MAP_LOOKUP_ELEM** does not
                           copy the **bpf_spin_lock** field to user space.
    
                         • Syscall with command **BPF_MAP_UPDATE_ELEM** , or
                           update from a BPF program, do not update the
                           **bpf_spin_lock** field.
    
                         • **bpf_spin_lock** cannot be on the stack or inside a
                           networking packet (it can only be inside of a map
                           values).
    
                         • **bpf_spin_lock** is available to root only.
    
                         • Tracing programs and socket filter programs cannot
                           use **bpf_spin_lock**() due to insufficient preemption
                           checks (but this may change in the future).
    
                         • **bpf_spin_lock** is not allowed in inner maps of
                           map-in-map.
    
                  **Return** 0
    
           **long bpf_spin_unlock(struct bpf_spin_lock ***_lock_**)**
    
                  **Description**
                         Release the _lock_ previously locked by a call to
                         **bpf_spin_lock**(_lock_).
    
                  **Return** 0
    
           **struct bpf_sock *bpf_sk_fullsock(struct bpf_sock ***_sk_**)**
    
                  **Description**
                         This helper gets a **struct bpf_sock** pointer such that
                         all the fields in this **bpf_sock** can be accessed.
    
                  **Return** A **struct bpf_sock** pointer on success, or **NULL** in
                         case of failure.
    
           **struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock ***_sk_**)**
    
                  **Description**
                         This helper gets a **struct bpf_tcp_sock** pointer from
                         a **struct bpf_sock** pointer.
    
                  **Return** A **struct bpf_tcp_sock** pointer on success, or **NULL** in
                         case of failure.
    
           **long bpf_skb_ecn_set_ce(struct sk_buff ***_skb_**)**
    
                  **Description**
                         Set ECN (Explicit Congestion Notification) field of
                         IP header to **CE**(Congestion Encountered) if current
                         value is **ECT**(ECN Capable Transport). Otherwise, do
                         nothing. Works with IPv6 and IPv4.
    
                  **Return** 1 if the **CE** flag is set (either by the current
                         helper call or because it was already present), 0 if
                         it is not set.
    
           **struct bpf_sock *bpf_get_listener_sock(struct bpf_sock ***_sk_**)**
    
                  **Description**
                         Return a **struct bpf_sock** pointer in **TCP_LISTEN**
                         state.  **bpf_sk_release**() is unnecessary and not
                         allowed.
    
                  **Return** A **struct bpf_sock** pointer on success, or **NULL** in
                         case of failure.
    
           **struct bpf_sock *bpf_skc_lookup_tcp(void ***_ctx_**, struct**
           **bpf_sock_tuple ***_tuple_**, u32** _tuple_size_**, u64** _netns_**, u64** _flags_**)**
    
                  **Description**
                         Look for TCP socket matching _tuple_ , optionally in a
                         child network namespace _netns_. The return value must
                         be checked, and if non-**NULL** , released via
                         **bpf_sk_release**().
    
                         This function is identical to **bpf_sk_lookup_tcp**(),
                         except that it also returns timewait or request
                         sockets. Use **bpf_sk_fullsock**() or **bpf_tcp_sock**() to
                         access the full structure.
    
                         This helper is available only if the kernel was
                         compiled with **CONFIG_NET** configuration option.
    
                  **Return** Pointer to **struct bpf_sock** , or **NULL** in case of
                         failure.  For sockets with reuseport option, the
                         **struct bpf_sock** result is from _reuse_**- >socks**[] using
                         the hash of the tuple.
    
           **long bpf_tcp_check_syncookie(void ***_sk_**, void ***_iph_**, u32** _iph_len_**,**
           **struct tcphdr ***_th_**, u32** _th_len_**)**
    
                  **Description**
                         Check whether _iph_ and _th_ contain a valid SYN cookie
                         ACK for the listening socket in _sk_.
    
                         _iph_ points to the start of the IPv4 or IPv6 header,
                         while _iph_len_ contains **sizeof**(**struct iphdr**) or
                         **sizeof**(**struct ipv6hdr**).
    
                         _th_ points to the start of the TCP header, while
                         _th_len_ contains the length of the TCP header (at
                         least **sizeof**(**struct tcphdr**)).
    
                  **Return** 0 if _iph_ and _th_ are a valid SYN cookie ACK, or a
                         negative error otherwise.
    
           **long bpf_sysctl_get_name(struct bpf_sysctl ***_ctx_**, char ***_buf_**, size_t**
           _buf_len_**, u64** _flags_**)**
    
                  **Description**
                         Get name of sysctl in /proc/sys/ and copy it into
                         provided by program buffer _buf_ of size _buf_len_.
    
                         The buffer is always NUL terminated, unless it's
                         zero-sized.
    
                         If _flags_ is zero, full name (e.g.
                         "net/ipv4/tcp_mem") is copied. Use
                         **BPF_F_SYSCTL_BASE_NAME** flag to copy base name only
                         (e.g. "tcp_mem").
    
                  **Return** Number of character copied (not including the
                         trailing NUL).
    
                         **-E2BIG** if the buffer wasn't big enough (_buf_ will
                         contain truncated name in this case).
    
           **long bpf_sysctl_get_current_value(struct bpf_sysctl ***_ctx_**, char**
           *****_buf_**, size_t** _buf_len_**)**
    
                  **Description**
                         Get current value of sysctl as it is presented in
                         /proc/sys (incl. newline, etc), and copy it as a
                         string into provided by program buffer _buf_ of size
                         _buf_len_.
    
                         The whole value is copied, no matter what file
                         position user space issued e.g. sys_read at.
    
                         The buffer is always NUL terminated, unless it's
                         zero-sized.
    
                  **Return** Number of character copied (not including the
                         trailing NUL).
    
                         **-E2BIG** if the buffer wasn't big enough (_buf_ will
                         contain truncated name in this case).
    
                         **-EINVAL** if current value was unavailable, e.g.
                         because sysctl is uninitialized and read returns
                         -EIO for it.
    
           **long bpf_sysctl_get_new_value(struct bpf_sysctl ***_ctx_**, char ***_buf_**,**
           **size_t** _buf_len_**)**
    
                  **Description**
                         Get new value being written by user space to sysctl
                         (before the actual write happens) and copy it as a
                         string into provided by program buffer _buf_ of size
                         _buf_len_.
    
                         User space may write new value at file position > 0.
    
                         The buffer is always NUL terminated, unless it's
                         zero-sized.
    
                  **Return** Number of character copied (not including the
                         trailing NUL).
    
                         **-E2BIG** if the buffer wasn't big enough (_buf_ will
                         contain truncated name in this case).
    
                         **-EINVAL** if sysctl is being read.
    
           **long bpf_sysctl_set_new_value(struct bpf_sysctl ***_ctx_**, const char**
           *****_buf_**, size_t** _buf_len_**)**
    
                  **Description**
                         Override new value being written by user space to
                         sysctl with value provided by program in buffer _buf_
                         of size _buf_len_.
    
                         _buf_ should contain a string in same form as provided
                         by user space on sysctl write.
    
                         User space may write new value at file position > 0.
                         To override the whole sysctl value file position
                         should be set to zero.
    
                  **Return** 0 on success.
    
                         **-E2BIG** if the _buf_len_ is too big.
    
                         **-EINVAL** if sysctl is being read.
    
           **long bpf_strtol(const char ***_buf_**, size_t** _buf_len_**, u64** _flags_**, long**
           *****_res_**)**
    
                  **Description**
                         Convert the initial part of the string from buffer
                         _buf_ of size _buf_len_ to a long integer according to
                         the given base and save the result in _res_.
    
                         The string may begin with an arbitrary amount of
                         white space (as determined by isspace(3)) followed
                         by a single optional '**-** ' sign.
    
                         Five least significant bits of _flags_ encode base,
                         other bits are currently unused.
    
                         Base must be either 8, 10, 16 or 0 to detect it
                         automatically similar to user space strtol(3).
    
                  **Return** Number of characters consumed on success. Must be
                         positive but no more than _buf_len_.
    
                         **-EINVAL** if no valid digits were found or unsupported
                         base was provided.
    
                         **-ERANGE** if resulting value was out of range.
    
           **long bpf_strtoul(const char ***_buf_**, size_t** _buf_len_**, u64** _flags_**,**
           **unsigned long ***_res_**)**
    
                  **Description**
                         Convert the initial part of the string from buffer
                         _buf_ of size _buf_len_ to an unsigned long integer
                         according to the given base and save the result in
                         _res_.
    
                         The string may begin with an arbitrary amount of
                         white space (as determined by isspace(3)).
    
                         Five least significant bits of _flags_ encode base,
                         other bits are currently unused.
    
                         Base must be either 8, 10, 16 or 0 to detect it
                         automatically similar to user space strtoul(3).
    
                  **Return** Number of characters consumed on success. Must be
                         positive but no more than _buf_len_.
    
                         **-EINVAL** if no valid digits were found or unsupported
                         base was provided.
    
                         **-ERANGE** if resulting value was out of range.
    
           **void *bpf_sk_storage_get(struct bpf_map ***_map_**, void ***_sk_**, void**
           *****_value_**, u64** _flags_**)**
    
                  **Description**
                         Get a bpf-local-storage from a _sk_.
    
                         Logically, it could be thought of getting the value
                         from a _map_ with _sk_ as the **key**.  From this
                         perspective,  the usage is not much different from
                         **bpf_map_lookup_elem**(_map_ , **&**_sk_) except this helper
                         enforces the key must be a full socket and the map
                         must be a **BPF_MAP_TYPE_SK_STORAGE** also.
    
                         Underneath, the value is stored locally at _sk_
                         instead of the _map_.  The _map_ is used as the
                         bpf-local-storage "type". The bpf-local-storage
                         "type" (i.e. the _map_) is searched against all
                         bpf-local-storages residing at _sk_.
    
                         _sk_ is a kernel **struct sock** pointer for LSM program.
                         _sk_ is a **struct bpf_sock** pointer for other program
                         types.
    
                         An optional _flags_ (**BPF_SK_STORAGE_GET_F_CREATE**) can
                         be used such that a new bpf-local-storage will be
                         created if one does not exist.  _value_ can be used
                         together with **BPF_SK_STORAGE_GET_F_CREATE** to specify
                         the initial value of a bpf-local-storage.  If _value_
                         is **NULL** , the new bpf-local-storage will be zero
                         initialized.
    
                  **Return** A bpf-local-storage pointer is returned on success.
    
                         **NULL** if not found or there was an error in adding a
                         new bpf-local-storage.
    
           **long bpf_sk_storage_delete(struct bpf_map ***_map_**, void ***_sk_**)**
    
                  **Description**
                         Delete a bpf-local-storage from a _sk_.
    
                  **Return** 0 on success.
    
                         **-ENOENT** if the bpf-local-storage cannot be found.
                         **-EINVAL** if sk is not a fullsock (e.g. a
                         request_sock).
    
           **long bpf_send_signal(u32** _sig_**)**
    
                  **Description**
                         Send signal _sig_ to the process of the current task.
                         The signal may be delivered to any of this process's
                         threads.
    
                  **Return** 0 on success or successfully queued.
    
                         **-EBUSY** if work queue under nmi is full.
    
                         **-EINVAL** if _sig_ is invalid.
    
                         **-EPERM** if no permission to send the _sig_.
    
                         **-EAGAIN** if bpf program can try again.
    
           **s64 bpf_tcp_gen_syncookie(void ***_sk_**, void ***_iph_**, u32** _iph_len_**, struct**
           **tcphdr ***_th_**, u32** _th_len_**)**
    
                  **Description**
                         Try to issue a SYN cookie for the packet with
                         corresponding IP/TCP headers, _iph_ and _th_ , on the
                         listening socket in _sk_.
    
                         _iph_ points to the start of the IPv4 or IPv6 header,
                         while _iph_len_ contains **sizeof**(**struct iphdr**) or
                         **sizeof**(**struct ipv6hdr**).
    
                         _th_ points to the start of the TCP header, while
                         _th_len_ contains the length of the TCP header with
                         options (at least **sizeof**(**struct tcphdr**)).
    
                  **Return** On success, lower 32 bits hold the generated SYN
                         cookie in followed by 16 bits which hold the MSS
                         value for that cookie, and the top 16 bits are
                         unused.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EINVAL** SYN cookie cannot be issued due to error
    
                         **-ENOENT** SYN cookie should not be issued (no SYN
                         flood)
    
                         **-EOPNOTSUPP** kernel configuration does not enable SYN
                         cookies
    
                         **-EPROTONOSUPPORT** IP packet version is not 4 or 6
    
           **long bpf_skb_output(void ***_ctx_**, struct bpf_map ***_map_**, u64** _flags_**,**
           **void ***_data_**, u64** _size_**)**
    
                  **Description**
                         Write raw _data_ blob into a special BPF perf event
                         held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**.
                         This perf event must have the following attributes:
                         **PERF_SAMPLE_RAW** as **sample_type** , **PERF_TYPE_SOFTWARE**
                         as **type** , and **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
    
                         The _flags_ are used to indicate the index in _map_ for
                         which the value must be put, masked with
                         **BPF_F_INDEX_MASK**.  Alternatively, _flags_ can be set
                         to **BPF_F_CURRENT_CPU** to indicate that the index of
                         the current CPU core should be used.
    
                         The value to write, of _size_ , is passed through eBPF
                         stack and pointed by _data_.
    
                         _ctx_ is a pointer to in-kernel struct sk_buff.
    
                         This helper is similar to **bpf_perf_event_output**()
                         but restricted to raw_tracepoint bpf programs.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_probe_read_user(void ***_dst_**, u32** _size_**, const void**
           *****_unsafe_ptr_**)**
    
                  **Description**
                         Safely attempt to read _size_ bytes from user space
                         address _unsafe_ptr_ and store the data in _dst_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_probe_read_kernel(void ***_dst_**, u32** _size_**, const void**
           *****_unsafe_ptr_**)**
    
                  **Description**
                         Safely attempt to read _size_ bytes from kernel space
                         address _unsafe_ptr_ and store the data in _dst_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_probe_read_user_str(void ***_dst_**, u32** _size_**, const void**
           *****_unsafe_ptr_**)**
    
                  **Description**
                         Copy a NUL terminated string from an unsafe user
                         address _unsafe_ptr_ to _dst_. The _size_ should include
                         the terminating NUL byte. In case the string length
                         is smaller than _size_ , the target is not padded with
                         further NUL bytes. If the string length is larger
                         than _size_ , just _size_ -1 bytes are copied and the last
                         byte is set to NUL.
    
                         On success, returns the number of bytes that were
                         written, including the terminal NUL. This makes this
                         helper useful in tracing programs for reading
                         strings, and more importantly to get its length at
                         runtime. See the following snippet:
    
                            SEC("kprobe/sys_open")
                            void bpf_sys_open(struct pt_regs *ctx)
                            {
                                    char buf[PATHLEN]; // PATHLEN is defined to 256
                                    int res = bpf_probe_read_user_str(buf, sizeof(buf),
                                                                      ctx->di);
    
                                    // Consume buf, for example push it to
                                    // userspace via bpf_perf_event_output(); we
                                    // can use res (the string length) as event
                                    // size, after checking its boundaries.
                            }
    
                         In comparison, using **bpf_probe_read_user**() helper
                         here instead to read the string would require to
                         estimate the length at compile time, and would often
                         result in copying more memory than necessary.
    
                         Another useful use case is when parsing individual
                         process arguments or individual environment
                         variables navigating _current_**- >mm->arg_start **and
                         _current_**- >mm->env_start**: using this helper and the
                         return value, one can quickly iterate at the right
                         offset of the memory area.
    
                  **Return** On success, the strictly positive length of the
                         output string, including the trailing NUL character.
                         On error, a negative value.
    
           **long bpf_probe_read_kernel_str(void ***_dst_**, u32** _size_**, const void**
           *****_unsafe_ptr_**)**
    
                  **Description**
                         Copy a NUL terminated string from an unsafe kernel
                         address _unsafe_ptr_ to _dst_. Same semantics as with
                         **bpf_probe_read_user_str**() apply.
    
                  **Return** On success, the strictly positive length of the
                         string, including the trailing NUL character. On
                         error, a negative value.
    
           **long bpf_tcp_send_ack(void ***_tp_**, u32** _rcv_nxt_**)**
    
                  **Description**
                         Send out a tcp-ack. _tp_ is the in-kernel struct
                         **tcp_sock**.  _rcv_nxt_ is the ack_seq to be sent out.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_send_signal_thread(u32** _sig_**)**
    
                  **Description**
                         Send signal _sig_ to the thread corresponding to the
                         current task.
    
                  **Return** 0 on success or successfully queued.
    
                         **-EBUSY** if work queue under nmi is full.
    
                         **-EINVAL** if _sig_ is invalid.
    
                         **-EPERM** if no permission to send the _sig_.
    
                         **-EAGAIN** if bpf program can try again.
    
           **u64 bpf_jiffies64(void)**
    
                  **Description**
                         Obtain the 64bit jiffies
    
                  **Return** The 64 bit jiffies
    
           **long bpf_read_branch_records(struct bpf_perf_event_data ***_ctx_**, void**
           *****_buf_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         For an eBPF program attached to a perf event,
                         retrieve the branch records (**struct**
                         **perf_branch_entry**) associated to _ctx_ and store it in
                         the buffer pointed by _buf_ up to size _size_ bytes.
    
                  **Return** On success, number of bytes written to _buf_. On
                         error, a negative value.
    
                         The _flags_ can be set to
                         **BPF_F_GET_BRANCH_RECORDS_SIZE** to instead return the
                         number of bytes required to store all the branch
                         entries. If this flag is set, _buf_ may be NULL.
    
                         **-EINVAL** if arguments invalid or **size** not a multiple
                         of **sizeof**(**struct perf_branch_entry**).
    
                         **-ENOENT** if architecture does not support branch
                         records.
    
           **long bpf_get_ns_current_pid_tgid(u64** _dev_**, u64** _ino_**, struct**
           **bpf_pidns_info ***_nsdata_**, u32** _size_**)**
    
                  **Description**
                         Returns 0 on success, values for _pid_ and _tgid_ as
                         seen from the current _namespace_ will be returned in
                         _nsdata_.
    
                  **Return** 0 on success, or one of the following in case of
                         failure:
    
                         **-EINVAL** if dev and inum supplied don't match dev_t
                         and inode number with nsfs of current task, or if
                         dev conversion to dev_t lost high bits.
    
                         **-ENOENT** if pidns does not exists for the current
                         task.
    
           **long bpf_xdp_output(void ***_ctx_**, struct bpf_map ***_map_**, u64** _flags_**,**
           **void ***_data_**, u64** _size_**)**
    
                  **Description**
                         Write raw _data_ blob into a special BPF perf event
                         held by _map_ of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**.
                         This perf event must have the following attributes:
                         **PERF_SAMPLE_RAW** as **sample_type** , **PERF_TYPE_SOFTWARE**
                         as **type** , and **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
    
                         The _flags_ are used to indicate the index in _map_ for
                         which the value must be put, masked with
                         **BPF_F_INDEX_MASK**.  Alternatively, _flags_ can be set
                         to **BPF_F_CURRENT_CPU** to indicate that the index of
                         the current CPU core should be used.
    
                         The value to write, of _size_ , is passed through eBPF
                         stack and pointed by _data_.
    
                         _ctx_ is a pointer to in-kernel struct xdp_buff.
    
                         This helper is similar to **bpf_perf_eventoutput**() but
                         restricted to raw_tracepoint bpf programs.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u64 bpf_get_netns_cookie(void ***_ctx_**)**
    
                  **Description**
                         Retrieve the cookie (generated by the kernel) of the
                         network namespace the input _ctx_ is associated with.
                         The network namespace cookie remains stable for its
                         lifetime and provides a global identifier that can
                         be assumed unique. If _ctx_ is NULL, then the helper
                         returns the cookie for the initial network
                         namespace. The cookie itself is very similar to that
                         of **bpf_get_socket_cookie**() helper, but for network
                         namespaces instead of sockets.
    
                  **Return** A 8-byte long opaque number.
    
           **u64 bpf_get_current_ancestor_cgroup_id(int** _ancestor_level_**)**
    
                  **Description**
                         Return id of cgroup v2 that is ancestor of the
                         cgroup associated with the current task at the
                         _ancestor_level_. The root cgroup is at _ancestor_level_
                         zero and each step down the hierarchy increments the
                         level. If _ancestor_level_ == level of cgroup
                         associated with the current task, then return value
                         will be the same as that of
                         **bpf_get_current_cgroup_id**().
    
                         The helper is useful to implement policies based on
                         cgroups that are upper in hierarchy than immediate
                         cgroup associated with the current task.
    
                         The format of returned id and helper limitations are
                         same as in **bpf_get_current_cgroup_id**().
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **long bpf_sk_assign(struct sk_buff ***_skb_**, void ***_sk_**, u64** _flags_**)**
    
                  **Description**
                         Helper is overloaded depending on BPF program type.
                         This description applies to **BPF_PROG_TYPE_SCHED_CLS**
                         and **BPF_PROG_TYPE_SCHED_ACT** programs.
    
                         Assign the _sk_ to the _skb_. When combined with
                         appropriate routing configuration to receive the
                         packet towards the socket, will cause _skb_ to be
                         delivered to the specified socket.  Subsequent
                         redirection of _skb_ via  **bpf_redirect**(),
                         **bpf_clone_redirect**() or other methods outside of BPF
                         may interfere with successful delivery to the
                         socket.
    
                         This operation is only valid from TC ingress path.
    
                         The _flags_ argument must be zero.
    
                  **Return** 0 on success, or a negative error in case of
                         failure:
    
                         **-EINVAL** if specified _flags_ are not supported.
    
                         **-ENOENT** if the socket is unavailable for assignment.
    
                         **-ENETUNREACH** if the socket is unreachable (wrong
                         netns).
    
                         **-EOPNOTSUPP** if the operation is not supported, for
                         example a call from outside of TC ingress.
    
           **long bpf_sk_assign(struct bpf_sk_lookup ***_ctx_**, struct bpf_sock ***_sk_**,**
           **u64** _flags_**)**
    
                  **Description**
                         Helper is overloaded depending on BPF program type.
                         This description applies to **BPF_PROG_TYPE_SK_LOOKUP**
                         programs.
    
                         Select the _sk_ as a result of a socket lookup.
    
                         For the operation to succeed passed socket must be
                         compatible with the packet description provided by
                         the _ctx_ object.
    
                         L4 protocol (**IPPROTO_TCP** or **IPPROTO_UDP**) must be an
                         exact match. While IP family (**AF_INET** or **AF_INET6**)
                         must be compatible, that is IPv6 sockets that are
                         not v6-only can be selected for IPv4 packets.
    
                         Only TCP listeners and UDP unconnected sockets can
                         be selected. _sk_ can also be NULL to reset any
                         previous selection.
    
                         _flags_ argument can combination of following values:
    
                         • **BPF_SK_LOOKUP_F_REPLACE** to override the previous
                           socket selection, potentially done by a BPF
                           program that ran before us.
    
                         • **BPF_SK_LOOKUP_F_NO_REUSEPORT** to skip
                           load-balancing within reuseport group for the
                           socket being selected.
    
                         On success _ctx- >sk_ will point to the selected
                         socket.
    
                  **Return** 0 on success, or a negative errno in case of
                         failure.
    
                         • **-EAFNOSUPPORT** if socket family (_sk- >family_) is not
                           compatible with packet family (_ctx- >family_).
    
                         • **-EEXIST** if socket has been already selected,
                           potentially by another program, and
                           **BPF_SK_LOOKUP_F_REPLACE** flag was not specified.
    
                         • **-EINVAL** if unsupported flags were specified.
    
                         • **-EPROTOTYPE** if socket L4 protocol (_sk- >protocol_)
                           doesn't match packet protocol (_ctx- >protocol_).
    
                         • **-ESOCKTNOSUPPORT** if socket is not in allowed state
                           (TCP listening or UDP unconnected).
    
           **u64 bpf_ktime_get_boot_ns(void)**
    
                  **Description**
                         Return the time elapsed since system boot, in
                         nanoseconds.  Does include the time the system was
                         suspended.  See: **clock_gettime**(**CLOCK_BOOTTIME**)
    
                  **Return** Current _ktime_.
    
           **long bpf_seq_printf(struct seq_file ***_m_**, const char ***_fmt_**, u32**
           _fmt_size_**, const void ***_data_**, u32** _data_len_**)**
    
                  **Description**
                         **bpf_seq_printf**() uses seq_file **seq_printf**() to print
                         out the format string.  The _m_ represents the
                         seq_file. The _fmt_ and _fmt_size_ are for the format
                         string itself. The _data_ and _data_len_ are format
                         string arguments. The _data_ are a **u64** array and
                         corresponding format string values are stored in the
                         array. For strings and pointers where pointees are
                         accessed, only the pointer values are stored in the
                         _data_ array.  The _data_len_ is the size of _data_ in
                         bytes - must be a multiple of 8.
    
                         Formats **%s** , **%p{i,I}{4,6}** requires to read kernel
                         memory.  Reading kernel memory may fail due to
                         either invalid address or valid address but
                         requiring a major memory fault. If reading kernel
                         memory fails, the string for **%s** will be an empty
                         string, and the ip address for **%p{i,I}{4,6}** will be
                         0. Not returning error to bpf program is consistent
                         with what **bpf_trace_printk**() does for now.
    
                  **Return** 0 on success, or a negative error in case of
                         failure:
    
                         **-EBUSY** if per-CPU memory copy buffer is busy, can
                         try again by returning 1 from bpf program.
    
                         **-EINVAL** if arguments are invalid, or if _fmt_ is
                         invalid/unsupported.
    
                         **-E2BIG** if _fmt_ contains too many format specifiers.
    
                         **-EOVERFLOW** if an overflow happened: The same object
                         will be tried again.
    
           **long bpf_seq_write(struct seq_file ***_m_**, const void ***_data_**, u32** _len_**)**
    
                  **Description**
                         **bpf_seq_write**() uses seq_file **seq_write**() to write
                         the data.  The _m_ represents the seq_file. The _data_
                         and _len_ represent the data to write in bytes.
    
                  **Return** 0 on success, or a negative error in case of
                         failure:
    
                         **-EOVERFLOW** if an overflow happened: The same object
                         will be tried again.
    
           **u64 bpf_sk_cgroup_id(void ***_sk_**)**
    
                  **Description**
                         Return the cgroup v2 id of the socket _sk_.
    
                         _sk_ must be a non-**NULL** pointer to a socket, e.g. one
                         returned from **bpf_sk_lookup_xxx**(),
                         **bpf_sk_fullsock**(), etc. The format of returned id is
                         same as in **bpf_skb_cgroup_id**().
    
                         This helper is available only if the kernel was
                         compiled with the **CONFIG_SOCK_CGROUP_DATA**
                         configuration option.
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **u64 bpf_sk_ancestor_cgroup_id(void ***_sk_**, int** _ancestor_level_**)**
    
                  **Description**
                         Return id of cgroup v2 that is ancestor of cgroup
                         associated with the _sk_ at the _ancestor_level_.  The
                         root cgroup is at _ancestor_level_ zero and each step
                         down the hierarchy increments the level. If
                         _ancestor_level_ == level of cgroup associated with
                         _sk_ , then return value will be same as that of
                         **bpf_sk_cgroup_id**().
    
                         The helper is useful to implement policies based on
                         cgroups that are upper in hierarchy than immediate
                         cgroup associated with _sk_.
    
                         The format of returned id and helper limitations are
                         same as in **bpf_sk_cgroup_id**().
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **long bpf_ringbuf_output(void ***_ringbuf_**, void ***_data_**, u64** _size_**, u64**
           _flags_**)**
    
                  **Description**
                         Copy _size_ bytes from _data_ into a ring buffer
                         _ringbuf_.  If **BPF_RB_NO_WAKEUP** is specified in _flags_ ,
                         no notification of new data availability is sent.
                         If **BPF_RB_FORCE_WAKEUP** is specified in _flags_ ,
                         notification of new data availability is sent
                         unconditionally.  If **0** is specified in _flags_ , an
                         adaptive notification of new data availability is
                         sent.
    
                         An adaptive notification is a notification sent
                         whenever the user-space process has caught up and
                         consumed all available payloads. In case the
                         user-space process is still processing a previous
                         payload, then no notification is needed as it will
                         process the newly added payload automatically.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **void *bpf_ringbuf_reserve(void ***_ringbuf_**, u64** _size_**, u64** _flags_**)**
    
                  **Description**
                         Reserve _size_ bytes of payload in a ring buffer
                         _ringbuf_.  _flags_ must be 0.
    
                  **Return** Valid pointer with _size_ bytes of memory available;
                         NULL, otherwise.
    
           **void bpf_ringbuf_submit(void ***_data_**, u64** _flags_**)**
    
                  **Description**
                         Submit reserved ring buffer sample, pointed to by
                         _data_.  If **BPF_RB_NO_WAKEUP** is specified in _flags_ , no
                         notification of new data availability is sent.  If
                         **BPF_RB_FORCE_WAKEUP** is specified in _flags_ ,
                         notification of new data availability is sent
                         unconditionally.  If **0** is specified in _flags_ , an
                         adaptive notification of new data availability is
                         sent.
    
                         See 'bpf_ringbuf_output()' for the definition of
                         adaptive notification.
    
                  **Return** Nothing. Always succeeds.
    
           **void bpf_ringbuf_discard(void ***_data_**, u64** _flags_**)**
    
                  **Description**
                         Discard reserved ring buffer sample, pointed to by
                         _data_.  If **BPF_RB_NO_WAKEUP** is specified in _flags_ , no
                         notification of new data availability is sent.  If
                         **BPF_RB_FORCE_WAKEUP** is specified in _flags_ ,
                         notification of new data availability is sent
                         unconditionally.  If **0** is specified in _flags_ , an
                         adaptive notification of new data availability is
                         sent.
    
                         See 'bpf_ringbuf_output()' for the definition of
                         adaptive notification.
    
                  **Return** Nothing. Always succeeds.
    
           **u64 bpf_ringbuf_query(void ***_ringbuf_**, u64** _flags_**)**
    
                  **Description**
                         Query various characteristics of provided ring
                         buffer. What exactly is queries is determined by
                         _flags_ :
    
                         • **BPF_RB_AVAIL_DATA** : Amount of data not yet
                           consumed.
    
                         • **BPF_RB_RING_SIZE** : The size of ring buffer.
    
                         • **BPF_RB_CONS_POS** : Consumer position (can wrap
                           around).
    
                         • **BPF_RB_PROD_POS** : Producer(s) position (can wrap
                           around).
    
                         Data returned is just a momentary snapshot of actual
                         values and could be inaccurate, so this facility
                         should be used to power heuristics and for
                         reporting, not to make 100% correct calculation.
    
                  **Return** Requested value, or 0, if _flags_ are not recognized.
    
           **long bpf_csum_level(struct sk_buff ***_skb_**, u64** _level_**)**
    
                  **Description**
                         Change the skbs checksum level by one layer up or
                         down, or reset it entirely to none in order to have
                         the stack perform checksum validation. The level is
                         applicable to the following protocols: TCP, UDP,
                         GRE, SCTP, FCOE. For example, a decap of | ETH | IP
                         | UDP | GUE | IP | TCP | into | ETH | IP | TCP |
                         through **bpf_skb_adjust_room**() helper with passing in
                         **BPF_F_ADJ_ROOM_NO_CSUM_RESET** flag would require one
                         call to **bpf_csum_level**() with **BPF_CSUM_LEVEL_DEC**
                         since the UDP header is removed. Similarly, an encap
                         of the latter into the former could be accompanied
                         by a helper call to **bpf_csum_level**() with
                         **BPF_CSUM_LEVEL_INC** if the skb is still intended to
                         be processed in higher layers of the stack instead
                         of just egressing at tc.
    
                         There are three supported level settings at this
                         time:
    
                         • **BPF_CSUM_LEVEL_INC** : Increases skb->csum_level for
                           skbs with CHECKSUM_UNNECESSARY.
    
                         • **BPF_CSUM_LEVEL_DEC** : Decreases skb->csum_level for
                           skbs with CHECKSUM_UNNECESSARY.
    
                         • **BPF_CSUM_LEVEL_RESET** : Resets skb->csum_level to 0
                           and sets CHECKSUM_NONE to force checksum
                           validation by the stack.
    
                         • **BPF_CSUM_LEVEL_QUERY** : No-op, returns the current
                           skb->csum_level.
    
                  **Return** 0 on success, or a negative error in case of
                         failure. In the case of **BPF_CSUM_LEVEL_QUERY** , the
                         current skb->csum_level is returned or the error
                         code -EACCES in case the skb is not subject to
                         CHECKSUM_UNNECESSARY.
    
           **struct tcp6_sock *bpf_skc_to_tcp6_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _tcp6_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **struct tcp_sock *bpf_skc_to_tcp_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _tcp_sock_ pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _tcp_timewait_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _tcp_request_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **struct udp6_sock *bpf_skc_to_udp6_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _udp6_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **long bpf_get_task_stack(struct task_struct ***_task_**, void ***_buf_**, u32**
           _size_**, u64** _flags_**)**
    
                  **Description**
                         Return a user or a kernel stack in bpf program
                         provided buffer.  Note: the user stack will only be
                         populated if the _task_ is the current task; all other
                         tasks will return -EOPNOTSUPP.  To achieve this, the
                         helper needs _task_ , which is a valid pointer to
                         **struct task_struct**. To store the stacktrace, the bpf
                         program provides _buf_ with a nonnegative _size_.
    
                         The last argument, _flags_ , holds the number of stack
                         frames to skip (from 0 to 255), masked with
                         **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to
                         set the following flags:
    
                         **BPF_F_USER_STACK**
                                Collect a user space stack instead of a
                                kernel stack.  The _task_ must be the current
                                task.
    
                         **BPF_F_USER_BUILD_ID**
                                Collect buildid+offset instead of ips for
                                user stack, only valid if **BPF_F_USER_STACK** is
                                also specified.
    
                         **bpf_get_task_stack**() can collect up to
                         **PERF_MAX_STACK_DEPTH** both kernel and user frames,
                         subject to sufficient large buffer size. Note that
                         this limit can be controlled with the **sysctl**
                         program, and that it should be manually increased in
                         order to profile long user stacks (such as stacks
                         for Java programs). To do so, use:
    
                            # sysctl kernel.perf_event_max_stack=<new value>
    
                  **Return** The non-negative copied _buf_ length equal to or less
                         than _size_ on success, or a negative error in case of
                         failure.
    
           **long bpf_load_hdr_opt(struct bpf_sock_ops ***_skops_**, void**
           *****_searchby_res_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Load header option.  Support reading a particular
                         TCP header option for bpf program
                         (**BPF_PROG_TYPE_SOCK_OPS**).
    
                         If _flags_ is 0, it will search the option from the
                         _skops_**- >skb_data**.  The comment in **struct bpf_sock_ops**
                         has details on what skb_data contains under
                         different _skops_**- >op**.
    
                         The first byte of the _searchby_res_ specifies the
                         kind that it wants to search.
    
                         If the searching kind is an experimental kind (i.e.
                         253 or 254 according to RFC6994).  It also needs to
                         specify the "magic" which is either 2 bytes or 4
                         bytes.  It then also needs to specify the size of
                         the magic by using the 2nd byte which is
                         "kind-length" of a TCP header option and the
                         "kind-length" also includes the first 2 bytes "kind"
                         and "kind-length" itself as a normal TCP header
                         option also does.
    
                         For example, to search experimental kind 254 with 2
                         byte magic 0xeB9F, the searchby_res should be [ 254,
                         4, 0xeB, 0x9F, 0, 0, .... 0 ].
    
                         To search for the standard window scale option (3),
                         the _searchby_res_ should be [ 3, 0, 0, .... 0 ].
                         Note, kind-length must be 0 for regular option.
    
                         Searching for No-Op (0) and End-of-Option-List (1)
                         are not supported.
    
                         _len_ must be at least 2 bytes which is the minimal
                         size of a header option.
    
                         Supported flags:
    
                         • **BPF_LOAD_HDR_OPT_TCP_SYN** to search from the
                           saved_syn packet or the just-received syn packet.
    
                  **Return** > 0 when found, the header option is copied to
                         _searchby_res_.  The return value is the total length
                         copied. On failure, a negative error code is
                         returned:
    
                         **-EINVAL** if a parameter is invalid.
    
                         **-ENOMSG** if the option is not found.
    
                         **-ENOENT** if no syn packet is available when
                         **BPF_LOAD_HDR_OPT_TCP_SYN** is used.
    
                         **-ENOSPC** if there is not enough space.  Only _len_
                         number of bytes are copied.
    
                         **-EFAULT** on failure to parse the header options in
                         the packet.
    
                         **-EPERM** if the helper cannot be used under the
                         current _skops_**- >op**.
    
           **long bpf_store_hdr_opt(struct bpf_sock_ops ***_skops_**, const void**
           *****_from_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Store header option.  The data will be copied from
                         buffer _from_ with length _len_ to the TCP header.
    
                         The buffer _from_ should have the whole option that
                         includes the kind, kind-length, and the actual
                         option data.  The _len_ must be at least kind-length
                         long.  The kind-length does not have to be 4 byte
                         aligned.  The kernel will take care of the padding
                         and setting the 4 bytes aligned value to th->doff.
    
                         This helper will check for duplicated option by
                         searching the same option in the outgoing skb.
    
                         This helper can only be called during
                         **BPF_SOCK_OPS_WRITE_HDR_OPT_CB**.
    
                  **Return** 0 on success, or negative error in case of failure:
    
                         **-EINVAL** If param is invalid.
    
                         **-ENOSPC** if there is not enough space in the header.
                         Nothing has been written
    
                         **-EEXIST** if the option already exists.
    
                         **-EFAULT** on failure to parse the existing header
                         options.
    
                         **-EPERM** if the helper cannot be used under the
                         current _skops_**- >op**.
    
           **long bpf_reserve_hdr_opt(struct bpf_sock_ops ***_skops_**, u32** _len_**, u64**
           _flags_**)**
    
                  **Description**
                         Reserve _len_ bytes for the bpf header option.  The
                         space will be used by **bpf_store_hdr_opt**() later in
                         **BPF_SOCK_OPS_WRITE_HDR_OPT_CB**.
    
                         If **bpf_reserve_hdr_opt**() is called multiple times,
                         the total number of bytes will be reserved.
    
                         This helper can only be called during
                         **BPF_SOCK_OPS_HDR_OPT_LEN_CB**.
    
                  **Return** 0 on success, or negative error in case of failure:
    
                         **-EINVAL** if a parameter is invalid.
    
                         **-ENOSPC** if there is not enough space in the header.
    
                         **-EPERM** if the helper cannot be used under the
                         current _skops_**- >op**.
    
           **void *bpf_inode_storage_get(struct bpf_map ***_map_**, void ***_inode_**, void**
           *****_value_**, u64** _flags_**)**
    
                  **Description**
                         Get a bpf_local_storage from an _inode_.
    
                         Logically, it could be thought of as getting the
                         value from a _map_ with _inode_ as the **key**.  From this
                         perspective,  the usage is not much different from
                         **bpf_map_lookup_elem**(_map_ , **&**_inode_) except this helper
                         enforces the key must be an inode and the map must
                         also be a **BPF_MAP_TYPE_INODE_STORAGE**.
    
                         Underneath, the value is stored locally at _inode_
                         instead of the _map_.  The _map_ is used as the
                         bpf-local-storage "type". The bpf-local-storage
                         "type" (i.e. the _map_) is searched against all
                         bpf_local_storage residing at _inode_.
    
                         An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**)
                         can be used such that a new bpf_local_storage will
                         be created if one does not exist.  _value_ can be used
                         together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to
                         specify the initial value of a bpf_local_storage.
                         If _value_ is **NULL** , the new bpf_local_storage will be
                         zero initialized.
    
                  **Return** A bpf_local_storage pointer is returned on success.
    
                         **NULL** if not found or there was an error in adding a
                         new bpf_local_storage.
    
           **int bpf_inode_storage_delete(struct bpf_map ***_map_**, void ***_inode_**)**
    
                  **Description**
                         Delete a bpf_local_storage from an _inode_.
    
                  **Return** 0 on success.
    
                         **-ENOENT** if the bpf_local_storage cannot be found.
    
           **long bpf_d_path(struct path ***_path_**, char ***_buf_**, u32** _sz_**)**
    
                  **Description**
                         Return full path for given **struct path** object, which
                         needs to be the kernel BTF _path_ object. The path is
                         returned in the provided buffer _buf_ of size _sz_ and
                         is zero terminated.
    
                  **Return** On success, the strictly positive length of the
                         string, including the trailing NUL character. On
                         error, a negative value.
    
           **long bpf_copy_from_user(void ***_dst_**, u32** _size_**, const void ***_user_ptr_**)**
    
                  **Description**
                         Read _size_ bytes from user space address _user_ptr_ and
                         store the data in _dst_. This is a wrapper of
                         **copy_from_user**().
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_snprintf_btf(char ***_str_**, u32** _str_size_**, struct btf_ptr**
           *****_ptr_**, u32** _btf_ptr_size_**, u64** _flags_**)**
    
                  **Description**
                         Use BTF to store a string representation of _ptr_ ->ptr
                         in _str_ , using _ptr_ ->type_id.  This value should
                         specify the type that _ptr_ ->ptr points to. LLVM
                         __builtin_btf_type_id(type, 1) can be used to look
                         up vmlinux BTF type ids. Traversing the data
                         structure using BTF, the type information and values
                         are stored in the first _str_size_ - 1 bytes of _str_.
                         Safe copy of the pointer data is carried out to
                         avoid kernel crashes during operation.  Smaller
                         types can use string space on the stack; larger
                         programs can use map data to store the string
                         representation.
    
                         The string can be subsequently shared with userspace
                         via bpf_perf_event_output() or ring buffer
                         interfaces.  bpf_trace_printk() is to be avoided as
                         it places too small a limit on string size to be
                         useful.
    
                         _flags_ is a combination of
    
                         **BTF_F_COMPACT**
                                no formatting around type information
    
                         **BTF_F_NONAME**
                                no struct/union member names/types
    
                         **BTF_F_PTR_RAW**
                                show raw (unobfuscated) pointer values;
                                equivalent to printk specifier %px.
    
                         **BTF_F_ZERO**
                                show zero-valued struct/union members; they
                                are not displayed by default
    
                  **Return** The number of bytes that were written (or would have
                         been written if output had to be truncated due to
                         string size), or a negative error in cases of
                         failure.
    
           **long bpf_seq_printf_btf(struct seq_file ***_m_**, struct btf_ptr ***_ptr_**,**
           **u32** _ptr_size_**, u64** _flags_**)**
    
                  **Description**
                         Use BTF to write to seq_write a string
                         representation of _ptr_ ->ptr, using _ptr_ ->type_id as
                         per bpf_snprintf_btf().  _flags_ are identical to
                         those used for bpf_snprintf_btf.
    
                  **Return** 0 on success or a negative error in case of failure.
    
           **u64 bpf_skb_cgroup_classid(struct sk_buff ***_skb_**)**
    
                  **Description**
                         See **bpf_get_cgroup_classid**() for the main
                         description.  This helper differs from
                         **bpf_get_cgroup_classid**() in that the cgroup v1
                         net_cls class is retrieved only from the _skb_ 's
                         associated socket instead of the current process.
    
                  **Return** The id is returned or 0 in case the id could not be
                         retrieved.
    
           **long bpf_redirect_neigh(u32** _ifindex_**, struct bpf_redir_neigh**
           *****_params_**, int** _plen_**, u64** _flags_**)**
    
                  **Description**
                         Redirect the packet to another net device of index
                         _ifindex_ and fill in L2 addresses from neighboring
                         subsystem. This helper is somewhat similar to
                         **bpf_redirect**(), except that it populates L2
                         addresses as well, meaning, internally, the helper
                         relies on the neighbor lookup for the L2 address of
                         the nexthop.
    
                         The helper will perform a FIB lookup based on the
                         skb's networking header to get the address of the
                         next hop, unless this is supplied by the caller in
                         the _params_ argument. The _plen_ argument indicates the
                         len of _params_ and should be set to 0 if _params_ is
                         NULL.
    
                         The _flags_ argument is reserved and must be 0. The
                         helper is currently only supported for tc BPF
                         program types, and enabled for IPv4 and IPv6
                         protocols.
    
                  **Return** The helper returns **TC_ACT_REDIRECT** on success or
                         **TC_ACT_SHOT** on error.
    
           **void *bpf_per_cpu_ptr(const void ***_percpu_ptr_**, u32** _cpu_**)**
    
                  **Description**
                         Take a pointer to a percpu ksym, _percpu_ptr_ , and
                         return a pointer to the percpu kernel variable on
                         _cpu_. A ksym is an extern variable decorated with
                         '__ksym'. For ksym, there is a global var (either
                         static or global) defined of the same name in the
                         kernel. The ksym is percpu if the global var is
                         percpu.  The returned pointer points to the global
                         percpu var on _cpu_.
    
                         bpf_per_cpu_ptr() has the same semantic as
                         per_cpu_ptr() in the kernel, except that
                         bpf_per_cpu_ptr() may return NULL. This happens if
                         _cpu_ is larger than nr_cpu_ids. The caller of
                         bpf_per_cpu_ptr() must check the returned value.
    
                  **Return** A pointer pointing to the kernel percpu variable on
                         _cpu_ , or NULL, if _cpu_ is invalid.
    
           **void *bpf_this_cpu_ptr(const void ***_percpu_ptr_**)**
    
                  **Description**
                         Take a pointer to a percpu ksym, _percpu_ptr_ , and
                         return a pointer to the percpu kernel variable on
                         this cpu. See the description of 'ksym' in
                         **bpf_per_cpu_ptr**().
    
                         bpf_this_cpu_ptr() has the same semantic as
                         this_cpu_ptr() in the kernel. Different from
                         **bpf_per_cpu_ptr**(), it would never return NULL.
    
                  **Return** A pointer pointing to the kernel percpu variable on
                         this cpu.
    
           **long bpf_redirect_peer(u32** _ifindex_**, u64** _flags_**)**
    
                  **Description**
                         Redirect the packet to another net device of index
                         _ifindex_.  This helper is somewhat similar to
                         **bpf_redirect**(), except that the redirection happens
                         to the _ifindex_ ' peer device and the netns switch
                         takes place from ingress to ingress without going
                         through the CPU's backlog queue.
    
                         The _flags_ argument is reserved and must be 0. The
                         helper is currently only supported for tc BPF
                         program types at the ingress hook and for veth and
                         netkit target device types. The peer device must
                         reside in a different network namespace.
    
                  **Return** The helper returns **TC_ACT_REDIRECT** on success or
                         **TC_ACT_SHOT** on error.
    
           **void *bpf_task_storage_get(struct bpf_map ***_map_**, struct task_struct**
           *****_task_**, void ***_value_**, u64** _flags_**)**
    
                  **Description**
                         Get a bpf_local_storage from the _task_.
    
                         Logically, it could be thought of as getting the
                         value from a _map_ with _task_ as the **key**.  From this
                         perspective,  the usage is not much different from
                         **bpf_map_lookup_elem**(_map_ , **&**_task_) except this helper
                         enforces the key must be a task_struct and the map
                         must also be a **BPF_MAP_TYPE_TASK_STORAGE**.
    
                         Underneath, the value is stored locally at _task_
                         instead of the _map_.  The _map_ is used as the
                         bpf-local-storage "type". The bpf-local-storage
                         "type" (i.e. the _map_) is searched against all
                         bpf_local_storage residing at _task_.
    
                         An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**)
                         can be used such that a new bpf_local_storage will
                         be created if one does not exist.  _value_ can be used
                         together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to
                         specify the initial value of a bpf_local_storage.
                         If _value_ is **NULL** , the new bpf_local_storage will be
                         zero initialized.
    
                  **Return** A bpf_local_storage pointer is returned on success.
    
                         **NULL** if not found or there was an error in adding a
                         new bpf_local_storage.
    
           **long bpf_task_storage_delete(struct bpf_map ***_map_**, struct**
           **task_struct ***_task_**)**
    
                  **Description**
                         Delete a bpf_local_storage from a _task_.
    
                  **Return** 0 on success.
    
                         **-ENOENT** if the bpf_local_storage cannot be found.
    
           **struct task_struct *bpf_get_current_task_btf(void)**
    
                  **Description**
                         Return a BTF pointer to the "current" task.  This
                         pointer can also be used in helpers that accept an
                         _ARG_PTR_TO_BTF_ID_ of type _task_struct_.
    
                  **Return** Pointer to the current task.
    
           **long bpf_bprm_opts_set(struct linux_binprm ***_bprm_**, u64** _flags_**)**
    
                  **Description**
                         Set or clear certain options on _bprm_ :
    
                         **BPF_F_BPRM_SECUREEXEC** Set the secureexec bit which
                         sets the **AT_SECURE** auxv for glibc. The bit is
                         cleared if the flag is not specified.
    
                  **Return -EINVAL** if invalid _flags_ are passed, zero otherwise.
    
           **u64 bpf_ktime_get_coarse_ns(void)**
    
                  **Description**
                         Return a coarse-grained version of the time elapsed
                         since system boot, in nanoseconds. Does not include
                         time the system was suspended.
    
                         See: **clock_gettime**(**CLOCK_MONOTONIC_COARSE**)
    
                  **Return** Current _ktime_.
    
           **long bpf_ima_inode_hash(struct inode ***_inode_**, void ***_dst_**, u32** _size_**)**
    
                  **Description**
                         Returns the stored IMA hash of the _inode_ (if it's
                         available).  If the hash is larger than _size_ , then
                         only _size_ bytes will be copied to _dst_
    
                  **Return** The **hash_algo** is returned on success, **-EOPNOTSUPP** if
                         IMA is disabled or **-EINVAL** if invalid arguments are
                         passed.
    
           **struct socket *bpf_sock_from_file(struct file ***_file_**)**
    
                  **Description**
                         If the given file represents a socket, returns the
                         associated socket.
    
                  **Return** A pointer to a struct socket on success or NULL if
                         the file is not a socket.
    
           **long bpf_check_mtu(void ***_ctx_**, u32** _ifindex_**, u32 ***_mtu_len_**, s32**
           _len_diff_**, u64** _flags_**)**
    
                  **Description**
                         Check packet size against exceeding MTU of net
                         device (based on _ifindex_).  This helper will likely
                         be used in combination with helpers that
                         adjust/change the packet size.
    
                         The argument _len_diff_ can be used for querying with
                         a planned size change. This allows to check MTU
                         prior to changing packet ctx. Providing a _len_diff_
                         adjustment that is larger than the actual packet
                         size (resulting in negative packet size) will in
                         principle not exceed the MTU, which is why it is not
                         considered a failure.  Other BPF helpers are needed
                         for performing the planned size change; therefore
                         the responsibility for catching a negative packet
                         size belongs in those helpers.
    
                         Specifying _ifindex_ zero means the MTU check is
                         performed against the current net device.  This is
                         practical if this isn't used prior to redirect.
    
                         On input _mtu_len_ must be a valid pointer, else
                         verifier will reject BPF program.  If the value
                         _mtu_len_ is initialized to zero then the ctx packet
                         size is use.  When value _mtu_len_ is provided as
                         input this specify the L3 length that the MTU check
                         is done against. Remember XDP and TC length operate
                         at L2, but this value is L3 as this correlate to MTU
                         and IP-header tot_len values which are L3 (similar
                         behavior as bpf_fib_lookup).
    
                         The Linux kernel route table can configure MTUs on a
                         more specific per route level, which is not provided
                         by this helper.  For route level MTU checks use the
                         **bpf_fib_lookup**() helper.
    
                         _ctx_ is either **struct xdp_md** for XDP programs or
                         **struct sk_buff** for tc cls_act programs.
    
                         The _flags_ argument can be a combination of one or
                         more of the following values:
    
                         **BPF_MTU_CHK_SEGS**
                                This flag will only works for _ctx_ **struct**
                                **sk_buff**.  If packet context contains extra
                                packet segment buffers (often knows as GSO
                                skb), then MTU check is harder to check at
                                this point, because in transmit path it is
                                possible for the skb packet to get
                                re-segmented (depending on net device
                                features).  This could still be a MTU
                                violation, so this flag enables performing
                                MTU check against segments, with a different
                                violation return code to tell it apart. Check
                                cannot use len_diff.
    
                         On return _mtu_len_ pointer contains the MTU value of
                         the net device.  Remember the net device configured
                         MTU is the L3 size, which is returned here and XDP
                         and TC length operate at L2.  Helper take this into
                         account for you, but remember when using MTU value
                         in your BPF-code.
    
                  **Return**
    
                         • 0 on success, and populate MTU value in _mtu_len_
                           pointer.
    
                         • < 0 if any input argument is invalid (_mtu_len_ not
                           updated)
    
                         MTU violations return positive values, but also
                         populate MTU value in _mtu_len_ pointer, as this can
                         be needed for implementing PMTU handing:
    
                         • **BPF_MTU_CHK_RET_FRAG_NEEDED**
    
                         • **BPF_MTU_CHK_RET_SEGS_TOOBIG**
    
           **long bpf_for_each_map_elem(struct bpf_map ***_map_**, void ***_callback_fn_**,**
           **void ***_callback_ctx_**, u64** _flags_**)**
    
                  **Description**
                         For each element in **map** , call **callback_fn** function
                         with **map** , **callback_ctx** and other map-specific
                         parameters.  The **callback_fn** should be a static
                         function and the **callback_ctx** should be a pointer to
                         the stack.  The **flags** is used to control certain
                         aspects of the helper.  Currently, the **flags** must be
                         0.
    
                         The following are a list of supported map types and
                         their respective expected callback signatures:
    
                         BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_PERCPU_HASH,
                         BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH,
                         BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PERCPU_ARRAY
    
                         long (*callback_fn)(struct bpf_map *map, const void
                         *key, void *value, void *ctx);
    
                         For per_cpu maps, the map_value is the value on the
                         cpu where the bpf_prog is running.
    
                         If **callback_fn** return 0, the helper will continue to
                         the next element. If return value is 1, the helper
                         will skip the rest of elements and return. Other
                         return values are not used now.
    
                  **Return** The number of traversed map elements for success,
                         **-EINVAL** for invalid **flags**.
    
           **long bpf_snprintf(char ***_str_**, u32** _str_size_**, const char ***_fmt_**, u64**
           *****_data_**, u32** _data_len_**)**
    
                  **Description**
                         Outputs a string into the **str** buffer of size
                         **str_size** based on a format string stored in a
                         read-only map pointed by **fmt**.
    
                         Each format specifier in **fmt** corresponds to one u64
                         element in the **data** array. For strings and pointers
                         where pointees are accessed, only the pointer values
                         are stored in the _data_ array. The _data_len_ is the
                         size of _data_ in bytes - must be a multiple of 8.
    
                         Formats **%s** and **%p{i,I}{4,6}** require to read kernel
                         memory. Reading kernel memory may fail due to either
                         invalid address or valid address but requiring a
                         major memory fault. If reading kernel memory fails,
                         the string for **%s** will be an empty string, and the
                         ip address for **%p{i,I}{4,6}** will be 0.  Not
                         returning error to bpf program is consistent with
                         what **bpf_trace_printk**() does for now.
    
                  **Return** The strictly positive length of the formatted
                         string, including the trailing zero character. If
                         the return value is greater than **str_size** , **str**
                         contains a truncated string, guaranteed to be
                         zero-terminated except when **str_size** is 0.
    
                         Or **-EBUSY** if the per-CPU memory copy buffer is busy.
    
           **long bpf_sys_bpf(u32** _cmd_**, void ***_attr_**, u32** _attr_size_**)**
    
                  **Description**
                         Execute bpf syscall with given arguments.
    
                  **Return** A syscall result.
    
           **long bpf_btf_find_by_name_kind(char ***_name_**, int** _name_sz_**, u32** _kind_**,**
           **int** _flags_**)**
    
                  **Description**
                         Find BTF type with given name and kind in vmlinux
                         BTF or in module's BTFs.
    
                  **Return** Returns btf_id and btf_obj_fd in lower and upper 32
                         bits.
    
           **long bpf_sys_close(u32** _fd_**)**
    
                  **Description**
                         Execute close syscall for given FD.
    
                  **Return** A syscall result.
    
           **long bpf_timer_init(struct bpf_timer ***_timer_**, struct bpf_map ***_map_**,**
           **u64** _flags_**)**
    
                  **Description**
                         Initialize the timer.  First 4 bits of _flags_ specify
                         clockid.  Only CLOCK_MONOTONIC, CLOCK_REALTIME,
                         CLOCK_BOOTTIME are allowed.  All other bits of _flags_
                         are reserved.  The verifier will reject the program
                         if _timer_ is not from the same _map_.
    
                  **Return** 0 on success.  **-EBUSY** if _timer_ is already
                         initialized.  **-EINVAL** if invalid _flags_ are passed.
                         **-EPERM** if _timer_ is in a map that doesn't have any
                         user references.  The user space should either hold
                         a file descriptor to a map with timers or pin such
                         map in bpffs. When map is unpinned or file
                         descriptor is closed all timers in the map will be
                         cancelled and freed.
    
           **long bpf_timer_set_callback(struct bpf_timer ***_timer_**, void**
           *****_callback_fn_**)**
    
                  **Description**
                         Configure the timer to call _callback_fn_ static
                         function.
    
                  **Return** 0 on success.  **-EINVAL** if _timer_ was not initialized
                         with bpf_timer_init() earlier.  **-EPERM** if _timer_ is
                         in a map that doesn't have any user references.  The
                         user space should either hold a file descriptor to a
                         map with timers or pin such map in bpffs. When map
                         is unpinned or file descriptor is closed all timers
                         in the map will be cancelled and freed.
    
           **long bpf_timer_start(struct bpf_timer ***_timer_**, u64** _nsecs_**, u64**
           _flags_**)**
    
                  **Description**
                         Set timer expiration N nanoseconds from the current
                         time. The configured callback will be invoked in
                         soft irq context on some cpu and will not repeat
                         unless another bpf_timer_start() is made.  In such
                         case the next invocation can migrate to a different
                         cpu.  Since struct bpf_timer is a field inside map
                         element the map owns the timer. The
                         bpf_timer_set_callback() will increment refcnt of
                         BPF program to make sure that callback_fn code stays
                         valid.  When user space reference to a map reaches
                         zero all timers in a map are cancelled and
                         corresponding program's refcnts are decremented.
                         This is done to make sure that Ctrl-C of a user
                         process doesn't leave any timers running. If map is
                         pinned in bpffs the callback_fn can re-arm itself
                         indefinitely.  bpf_map_update/delete_elem() helpers
                         and user space sys_bpf commands cancel and free the
                         timer in the given map element.  The map can contain
                         timers that invoke callback_fn-s from different
                         programs. The same callback_fn can serve different
                         timers from different maps if key/value layout
                         matches across maps.  Every bpf_timer_set_callback()
                         can have different callback_fn.
    
                         _flags_ can be one of:
    
                         **BPF_F_TIMER_ABS**
                                Start the timer in absolute expire value
                                instead of the default relative one.
    
                         **BPF_F_TIMER_CPU_PIN**
                                Timer will be pinned to the CPU of the
                                caller.
    
                  **Return** 0 on success.  **-EINVAL** if _timer_ was not initialized
                         with bpf_timer_init() earlier or invalid _flags_ are
                         passed.
    
           **long bpf_timer_cancel(struct bpf_timer ***_timer_**)**
    
                  **Description**
                         Cancel the timer and wait for callback_fn to finish
                         if it was running.
    
                  **Return** 0 if the timer was not active.  1 if the timer was
                         active.  **-EINVAL** if _timer_ was not initialized with
                         bpf_timer_init() earlier.  **-EDEADLK** if callback_fn
                         tried to call bpf_timer_cancel() on its own timer
                         which would have led to a deadlock otherwise.
    
           **u64 bpf_get_func_ip(void ***_ctx_**)**
    
                  **Description**
                         Get address of the traced function (for tracing and
                         kprobe programs).
    
                         When called for kprobe program attached as uprobe it
                         returns probe address for both entry and return
                         uprobe.
    
                  **Return** Address of the traced function for kprobe.  0 for
                         kprobes placed within the function (not at the
                         entry).  Address of the probe for uprobe and return
                         uprobe.
    
           **u64 bpf_get_attach_cookie(void ***_ctx_**)**
    
                  **Description**
                         Get bpf_cookie value provided (optionally) during
                         the program attachment. It might be different for
                         each individual attachment, even if BPF program
                         itself is the same.  Expects BPF program context _ctx_
                         as a first argument.
    
                         **Supported for the following program types:**
    
                                • kprobe/uprobe;
    
                                • tracepoint;
    
                                • perf_event.
    
                  **Return** Value specified by user at BPF link
                         creation/attachment time or 0, if it was not
                         specified.
    
           **long bpf_task_pt_regs(struct task_struct ***_task_**)**
    
                  **Description**
                         Get the struct pt_regs associated with **task**.
    
                  **Return** A pointer to struct pt_regs.
    
           **long bpf_get_branch_snapshot(void ***_entries_**, u32** _size_**, u64** _flags_**)**
    
                  **Description**
                         Get branch trace from hardware engines like Intel
                         LBR. The hardware engine is stopped shortly after
                         the helper is called. Therefore, the user need to
                         filter branch entries based on the actual use case.
                         To capture branch trace before the trigger point of
                         the BPF program, the helper should be called at the
                         beginning of the BPF program.
    
                         The data is stored as struct perf_branch_entry into
                         output buffer _entries_. _size_ is the size of _entries_
                         in bytes.  _flags_ is reserved for now and must be
                         zero.
    
                  **Return** On success, number of bytes written to _buf_. On
                         error, a negative value.
    
                         **-EINVAL** if _flags_ is not zero.
    
                         **-ENOENT** if architecture does not support branch
                         records.
    
           **long bpf_trace_vprintk(const char ***_fmt_**, u32** _fmt_size_**, const void**
           *****_data_**, u32** _data_len_**)**
    
                  **Description**
                         Behaves like **bpf_trace_printk**() helper, but takes an
                         array of u64 to format and can handle more format
                         args as a result.
    
                         Arguments are to be used as in **bpf_seq_printf**()
                         helper.
    
                  **Return** The number of bytes written to the buffer, or a
                         negative error in case of failure.
    
           **struct unix_sock *bpf_skc_to_unix_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _unix_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **long bpf_kallsyms_lookup_name(const char ***_name_**, int** _name_sz_**, int**
           _flags_**, u64 ***_res_**)**
    
                  **Description**
                         Get the address of a kernel symbol, returned in _res_.
                         _res_ is set to 0 if the symbol is not found.
    
                  **Return** On success, zero. On error, a negative value.
    
                         **-EINVAL** if _flags_ is not zero.
    
                         **-EINVAL** if string _name_ is not the same size as
                         _name_sz_.
    
                         **-ENOENT** if symbol is not found.
    
                         **-EPERM** if caller does not have permission to obtain
                         kernel address.
    
           **long bpf_find_vma(struct task_struct ***_task_**, u64** _addr_**, void**
           *****_callback_fn_**, void ***_callback_ctx_**, u64** _flags_**)**
    
                  **Description**
                         Find vma of _task_ that contains _addr_ , call
                         _callback_fn_ function with _task_ , _vma_ , and
                         _callback_ctx_.  The _callback_fn_ should be a static
                         function and the _callback_ctx_ should be a pointer to
                         the stack.  The _flags_ is used to control certain
                         aspects of the helper.  Currently, the _flags_ must be
                         0.
    
                         The expected callback signature is
    
                         long (*callback_fn)(struct task_struct *task, struct
                         vm_area_struct *vma, void *callback_ctx);
    
                  **Return** 0 on success.  **-ENOENT** if _task- >mm_ is NULL, or no
                         vma contains _addr_.  **-EBUSY** if failed to try lock
                         mmap_lock.  **-EINVAL** for invalid **flags**.
    
           **long bpf_loop(u32** _nr_loops_**, void ***_callback_fn_**, void ***_callback_ctx_**,**
           **u64** _flags_**)**
    
                  **Description**
                         For **nr_loops** , call **callback_fn** function with
                         **callback_ctx** as the context parameter.  The
                         **callback_fn** should be a static function and the
                         **callback_ctx** should be a pointer to the stack.  The
                         **flags** is used to control certain aspects of the
                         helper.  Currently, the **flags** must be 0. Currently,
                         nr_loops is limited to 1 << 23 (~8 million) loops.
    
                         long (*callback_fn)(u64 index, void *ctx);
    
                         where **index** is the current index in the loop. The
                         index is zero-indexed.
    
                         If **callback_fn** returns 0, the helper will continue
                         to the next loop. If return value is 1, the helper
                         will skip the rest of the loops and return. Other
                         return values are not used now, and will be rejected
                         by the verifier.
    
                  **Return** The number of loops performed, **-EINVAL** for invalid
                         **flags** , **-E2BIG** if **nr_loops** exceeds the maximum number
                         of loops.
    
           **long bpf_strncmp(const char ***_s1_**, u32** _s1_sz_**, const char ***_s2_**)**
    
                  **Description**
                         Do strncmp() between **s1** and **s2**. **s1** doesn't need to
                         be null-terminated and **s1_sz** is the maximum storage
                         size of **s1**. **s2** must be a read-only string.
    
                  **Return** An integer less than, equal to, or greater than zero
                         if the first **s1_sz** bytes of **s1** is found to be less
                         than, to match, or be greater than **s2**.
    
           **long bpf_get_func_arg(void ***_ctx_**, u32** _n_**, u64 ***_value_**)**
    
                  **Description**
                         Get **n** -th argument register (zero based) of the
                         traced function (for tracing programs) returned in
                         **value**.
    
                  **Return** 0 on success.  **-EINVAL** if n >= argument register
                         count of traced function.
    
           **long bpf_get_func_ret(void ***_ctx_**, u64 ***_value_**)**
    
                  **Description**
                         Get return value of the traced function (for tracing
                         programs) in **value**.
    
                  **Return** 0 on success.  **-EOPNOTSUPP** for tracing programs
                         other than BPF_TRACE_FEXIT or BPF_MODIFY_RETURN.
    
           **long bpf_get_func_arg_cnt(void ***_ctx_**)**
    
                  **Description**
                         Get number of registers of the traced function (for
                         tracing programs) where function arguments are
                         stored in these registers.
    
                  **Return** The number of argument registers of the traced
                         function.
    
           **int bpf_get_retval(void)**
    
                  **Description**
                         Get the BPF program's return value that will be
                         returned to the upper layers.
    
                         This helper is currently supported by cgroup
                         programs and only by the hooks where BPF program's
                         return value is returned to the userspace via errno.
    
                  **Return** The BPF program's return value.
    
           **int bpf_set_retval(int** _retval_**)**
    
                  **Description**
                         Set the BPF program's return value that will be
                         returned to the upper layers.
    
                         This helper is currently supported by cgroup
                         programs and only by the hooks where BPF program's
                         return value is returned to the userspace via errno.
    
                         Note that there is the following corner case where
                         the program exports an error via bpf_set_retval but
                         signals success via 'return 1':
                            bpf_set_retval(-EPERM); return 1;
    
                         In this case, the BPF program's return value will
                         use helper's -EPERM. This still holds true for
                         cgroup/bind{4,6} which supports extra 'return 3'
                         success case.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **u64 bpf_xdp_get_buff_len(struct xdp_buff ***_xdp_md_**)**
    
                  **Description**
                         Get the total size of a given xdp buff (linear and
                         paged area)
    
                  **Return** The total size of a given xdp buffer.
    
           **long bpf_xdp_load_bytes(struct xdp_buff ***_xdp_md_**, u32** _offset_**, void**
           *****_buf_**, u32** _len_**)**
    
                  **Description**
                         This helper is provided as an easy way to load data
                         from a xdp buffer. It can be used to load _len_ bytes
                         from _offset_ from the frame associated to _xdp_md_ ,
                         into the buffer pointed by _buf_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_xdp_store_bytes(struct xdp_buff ***_xdp_md_**, u32** _offset_**, void**
           *****_buf_**, u32** _len_**)**
    
                  **Description**
                         Store _len_ bytes from buffer _buf_ into the frame
                         associated to _xdp_md_ , at _offset_.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **long bpf_copy_from_user_task(void ***_dst_**, u32** _size_**, const void**
           *****_user_ptr_**, struct task_struct ***_tsk_**, u64** _flags_**)**
    
                  **Description**
                         Read _size_ bytes from user space address _user_ptr_ in
                         _tsk_ 's address space, and stores the data in _dst_.
                         _flags_ is not used yet and is provided for future
                         extensibility. This helper can only be used by
                         sleepable programs.
    
                  **Return** 0 on success, or a negative error in case of
                         failure. On error _dst_ buffer is zeroed out.
    
           **long bpf_skb_set_tstamp(struct sk_buff ***_skb_**, u64** _tstamp_**, u32**
           _tstamp_type_**)**
    
                  **Description**
                         Change the __sk_buff->tstamp_type to _tstamp_type_ and
                         set _tstamp_ to the __sk_buff->tstamp together.
    
                         If there is no need to change the
                         __sk_buff->tstamp_type, the tstamp value can be
                         directly written to __sk_buff->tstamp instead.
    
                         BPF_SKB_TSTAMP_DELIVERY_MONO is the only tstamp that
                         will be kept during bpf_redirect_*().  A non zero
                         _tstamp_ must be used with the
                         BPF_SKB_TSTAMP_DELIVERY_MONO _tstamp_type_.
    
                         A BPF_SKB_TSTAMP_UNSPEC _tstamp_type_ can only be used
                         with a zero _tstamp_.
    
                         Only IPv4 and IPv6 skb->protocol are supported.
    
                         This function is most useful when it needs to set a
                         mono delivery time to __sk_buff->tstamp and then
                         bpf_redirect_*() to the egress of an iface.  For
                         example, changing the (rcv) timestamp in
                         __sk_buff->tstamp at ingress to a mono delivery time
                         and then bpf_redirect_*() to  <sch_fq@phy-dev> .
    
                  **Return** 0 on success.  **-EINVAL** for invalid input **-EOPNOTSUPP**
                         for unsupported protocol
    
           **long bpf_ima_file_hash(struct file ***_file_**, void ***_dst_**, u32** _size_**)**
    
                  **Description**
                         Returns a calculated IMA hash of the _file_.  If the
                         hash is larger than _size_ , then only _size_ bytes will
                         be copied to _dst_
    
                  **Return** The **hash_algo** is returned on success, **-EOPNOTSUPP** if
                         the hash calculation failed or **-EINVAL** if invalid
                         arguments are passed.
    
           **void *bpf_kptr_xchg(void ***_dst_**, void ***_ptr_**)**
    
                  **Description**
                         Exchange kptr at pointer _dst_ with _ptr_ , and return
                         the old value.  _dst_ can be map value or local kptr.
                         _ptr_ can be NULL, otherwise it must be a referenced
                         pointer which will be released when this helper is
                         called.
    
                  **Return** The old value of kptr (which can be NULL). The
                         returned pointer if not NULL, is a reference which
                         must be released using its corresponding release
                         function, or moved into a BPF map before program
                         exit.
    
           **void *bpf_map_lookup_percpu_elem(struct bpf_map ***_map_**, const void**
           *****_key_**, u32** _cpu_**)**
    
                  **Description**
                         Perform a lookup in _percpu map_ for an entry
                         associated to _key_ on _cpu_.
    
                  **Return** Map value associated to _key_ on _cpu_ , or **NULL** if no
                         entry was found or _cpu_ is invalid.
    
           **struct mptcp_sock *bpf_skc_to_mptcp_sock(void ***_sk_**)**
    
                  **Description**
                         Dynamically cast a _sk_ pointer to a _mptcp_sock_
                         pointer.
    
                  **Return** _sk_ if casting is valid, or **NULL** otherwise.
    
           **long bpf_dynptr_from_mem(void ***_data_**, u32** _size_**, u64** _flags_**, struct**
           **bpf_dynptr ***_ptr_**)**
    
                  **Description**
                         Get a dynptr to local memory _data_.
    
                         _data_ must be a ptr to a map value.  The maximum _size_
                         supported is DYNPTR_MAX_SIZE.  _flags_ is currently
                         unused.
    
                  **Return** 0 on success, -E2BIG if the size exceeds
                         DYNPTR_MAX_SIZE, -EINVAL if flags is not 0.
    
           **long bpf_ringbuf_reserve_dynptr(void ***_ringbuf_**, u32** _size_**, u64**
           _flags_**, struct bpf_dynptr ***_ptr_**)**
    
                  **Description**
                         Reserve _size_ bytes of payload in a ring buffer
                         _ringbuf_ through the dynptr interface. _flags_ must be
                         0.
    
                         Please note that a corresponding
                         bpf_ringbuf_submit_dynptr or
                         bpf_ringbuf_discard_dynptr must be called on _ptr_ ,
                         even if the reservation fails. This is enforced by
                         the verifier.
    
                  **Return** 0 on success, or a negative error in case of
                         failure.
    
           **void bpf_ringbuf_submit_dynptr(struct bpf_dynptr ***_ptr_**, u64** _flags_**)**
    
                  **Description**
                         Submit reserved ring buffer sample, pointed to by
                         _data_ , through the dynptr interface. This is a no-op
                         if the dynptr is invalid/null.
    
                         For more information on _flags_ , please see
                         'bpf_ringbuf_submit'.
    
                  **Return** Nothing. Always succeeds.
    
           **void bpf_ringbuf_discard_dynptr(struct bpf_dynptr ***_ptr_**, u64** _flags_**)**
    
                  **Description**
                         Discard reserved ring buffer sample through the
                         dynptr interface. This is a no-op if the dynptr is
                         invalid/null.
    
                         For more information on _flags_ , please see
                         'bpf_ringbuf_discard'.
    
                  **Return** Nothing. Always succeeds.
    
           **long bpf_dynptr_read(void ***_dst_**, u32** _len_**, const struct bpf_dynptr**
           *****_src_**, u32** _offset_**, u64** _flags_**)**
    
                  **Description**
                         Read _len_ bytes from _src_ into _dst_ , starting from
                         _offset_ into _src_.  _flags_ is currently unused.
    
                  **Return** 0 on success, -E2BIG if _offset_ + _len_ exceeds the
                         length of _src_ 's data, -EINVAL if _src_ is an invalid
                         dynptr or if _flags_ is not 0.
    
           **long bpf_dynptr_write(const struct bpf_dynptr ***_dst_**, u32** _offset_**,**
           **void ***_src_**, u32** _len_**, u64** _flags_**)**
    
                  **Description**
                         Write _len_ bytes from _src_ into _dst_ , starting from
                         _offset_ into _dst_.
    
                         _flags_ must be 0 except for skb-type dynptrs.
    
                         **For skb-type dynptrs:**
    
                                • All data slices of the dynptr are
                                  automatically invalidated after
                                  **bpf_dynptr_write**(). This is because writing
                                  may pull the skb and change the underlying
                                  packet buffer.
    
                                • For _flags_ , please see the flags accepted by
                                  **bpf_skb_store_bytes**().
    
                  **Return** 0 on success, -E2BIG if _offset_ + _len_ exceeds the
                         length of _dst_ 's data, -EINVAL if _dst_ is an invalid
                         dynptr or if _dst_ is a read-only dynptr or if _flags_
                         is not correct. For skb-type dynptrs, other errors
                         correspond to errors returned by
                         **bpf_skb_store_bytes**().
    
           **void *bpf_dynptr_data(const struct bpf_dynptr ***_ptr_**, u32** _offset_**,**
           **u32** _len_**)**
    
                  **Description**
                         Get a pointer to the underlying dynptr data.
    
                         _len_ must be a statically known value. The returned
                         data slice is invalidated whenever the dynptr is
                         invalidated.
    
                         skb and xdp type dynptrs may not use
                         bpf_dynptr_data. They should instead use
                         bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
    
                  **Return** Pointer to the underlying dynptr data, NULL if the
                         dynptr is read-only, if the dynptr is invalid, or if
                         the offset and length is out of bounds.
    
           **s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr ***_iph_**, struct**
           **tcphdr ***_th_**, u32** _th_len_**)**
    
                  **Description**
                         Try to issue a SYN cookie for the packet with
                         corresponding IPv4/TCP headers, _iph_ and _th_ , without
                         depending on a listening socket.
    
                         _iph_ points to the IPv4 header.
    
                         _th_ points to the start of the TCP header, while
                         _th_len_ contains the length of the TCP header (at
                         least **sizeof**(**struct tcphdr**)).
    
                  **Return** On success, lower 32 bits hold the generated SYN
                         cookie in followed by 16 bits which hold the MSS
                         value for that cookie, and the top 16 bits are
                         unused.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EINVAL** if _th_len_ is invalid.
    
           **s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr ***_iph_**, struct**
           **tcphdr ***_th_**, u32** _th_len_**)**
    
                  **Description**
                         Try to issue a SYN cookie for the packet with
                         corresponding IPv6/TCP headers, _iph_ and _th_ , without
                         depending on a listening socket.
    
                         _iph_ points to the IPv6 header.
    
                         _th_ points to the start of the TCP header, while
                         _th_len_ contains the length of the TCP header (at
                         least **sizeof**(**struct tcphdr**)).
    
                  **Return** On success, lower 32 bits hold the generated SYN
                         cookie in followed by 16 bits which hold the MSS
                         value for that cookie, and the top 16 bits are
                         unused.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EINVAL** if _th_len_ is invalid.
    
                         **-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
    
           **long bpf_tcp_raw_check_syncookie_ipv4(struct iphdr ***_iph_**, struct**
           **tcphdr ***_th_**)**
    
                  **Description**
                         Check whether _iph_ and _th_ contain a valid SYN cookie
                         ACK without depending on a listening socket.
    
                         _iph_ points to the IPv4 header.
    
                         _th_ points to the TCP header.
    
                  **Return** 0 if _iph_ and _th_ are a valid SYN cookie ACK.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EACCES** if the SYN cookie is not valid.
    
           **long bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr ***_iph_**, struct**
           **tcphdr ***_th_**)**
    
                  **Description**
                         Check whether _iph_ and _th_ contain a valid SYN cookie
                         ACK without depending on a listening socket.
    
                         _iph_ points to the IPv6 header.
    
                         _th_ points to the TCP header.
    
                  **Return** 0 if _iph_ and _th_ are a valid SYN cookie ACK.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EACCES** if the SYN cookie is not valid.
    
                         **-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.
    
           **u64 bpf_ktime_get_tai_ns(void)**
    
                  **Description**
                         A nonsettable system-wide clock derived from
                         wall-clock time but ignoring leap seconds.  This
                         clock does not experience discontinuities and
                         backwards jumps caused by NTP inserting leap seconds
                         as CLOCK_REALTIME does.
    
                         See: **clock_gettime**(**CLOCK_TAI**)
    
                  **Return** Current _ktime_.
    
           **long bpf_user_ringbuf_drain(struct bpf_map ***_map_**, void**
           *****_callback_fn_**, void ***_ctx_**, u64** _flags_**)**
    
                  **Description**
                         Drain samples from the specified user ring buffer,
                         and invoke the provided callback for each such
                         sample:
    
                         long (*callback_fn)(const struct bpf_dynptr *dynptr,
                         void *ctx);
    
                         If **callback_fn** returns 0, the helper will continue
                         to try and drain the next sample, up to a maximum of
                         BPF_MAX_USER_RINGBUF_SAMPLES samples. If the return
                         value is 1, the helper will skip the rest of the
                         samples and return. Other return values are not used
                         now, and will be rejected by the verifier.
    
                  **Return** The number of drained samples if no error was
                         encountered while draining samples, or 0 if no
                         samples were present in the ring buffer. If a
                         user-space producer was epoll-waiting on this map,
                         and at least one sample was drained, they will
                         receive an event notification notifying them of
                         available space in the ring buffer. If the
                         BPF_RB_NO_WAKEUP flag is passed to this function, no
                         wakeup notification will be sent. If the
                         BPF_RB_FORCE_WAKEUP flag is passed, a wakeup
                         notification will be sent even if no sample was
                         drained.
    
                         On failure, the returned value is one of the
                         following:
    
                         **-EBUSY** if the ring buffer is contended, and another
                         calling context was concurrently draining the ring
                         buffer.
    
                         **-EINVAL** if user-space is not properly tracking the
                         ring buffer due to the producer position not being
                         aligned to 8 bytes, a sample not being aligned to 8
                         bytes, or the producer position not matching the
                         advertised length of a sample.
    
                         **-E2BIG** if user-space has tried to publish a sample
                         which is larger than the size of the ring buffer, or
                         which cannot fit within a struct bpf_dynptr.
    
           **void *bpf_cgrp_storage_get(struct bpf_map ***_map_**, struct cgroup**
           *****_cgroup_**, void ***_value_**, u64** _flags_**)**
    
                  **Description**
                         Get a bpf_local_storage from the _cgroup_.
    
                         Logically, it could be thought of as getting the
                         value from a _map_ with _cgroup_ as the **key**.  From this
                         perspective,  the usage is not much different from
                         **bpf_map_lookup_elem**(_map_ , **&**_cgroup_) except this helper
                         enforces the key must be a cgroup struct and the map
                         must also be a **BPF_MAP_TYPE_CGRP_STORAGE**.
    
                         In reality, the local-storage value is embedded
                         directly inside of the _cgroup_ object itself, rather
                         than being located in the **BPF_MAP_TYPE_CGRP_STORAGE**
                         map. When the local-storage value is queried for
                         some _map_ on a _cgroup_ object, the kernel will perform
                         an O(n) iteration over all of the live local-storage
                         values for that _cgroup_ object until the
                         local-storage value for the _map_ is found.
    
                         An optional _flags_ (**BPF_LOCAL_STORAGE_GET_F_CREATE**)
                         can be used such that a new bpf_local_storage will
                         be created if one does not exist.  _value_ can be used
                         together with **BPF_LOCAL_STORAGE_GET_F_CREATE** to
                         specify the initial value of a bpf_local_storage.
                         If _value_ is **NULL** , the new bpf_local_storage will be
                         zero initialized.
    
                  **Return** A bpf_local_storage pointer is returned on success.
    
                         **NULL** if not found or there was an error in adding a
                         new bpf_local_storage.
    
           **long bpf_cgrp_storage_delete(struct bpf_map ***_map_**, struct cgroup**
           *****_cgroup_**)**
    
                  **Description**
                         Delete a bpf_local_storage from a _cgroup_.
    
                  **Return** 0 on success.
    
                         **-ENOENT** if the bpf_local_storage cannot be found.
    


## EXAMPLES



           Example usage for most of the eBPF helpers listed in this manual
           page are available within the Linux kernel sources, at the
           following locations:
    
           • _samples/bpf/_
    
           • _tools/testing/selftests/bpf/_
    


## LICENSE



           eBPF programs can have an associated license, passed along with
           the bytecode instructions to the kernel when the programs are
           loaded. The format for that string is identical to the one in use
           for kernel modules (Dual licenses, such as "Dual BSD/GPL", may be
           used). Some helper functions are only accessible to programs that
           are compatible with the GNU General Public License (GNU GPL).
    
           In order to use such helpers, the eBPF program must be loaded with
           the correct license string passed (via **attr**) to the **bpf**() system
           call, and this generally translates into the C source code of the
           program containing a line similar to the following:
    
              char ____license[] __attribute__((section("license"), used)) = "GPL";
    


## IMPLEMENTATION



           This manual page is an effort to document the existing eBPF helper
           functions.  But as of this writing, the BPF sub-system is under
           heavy development. New eBPF program or map types are added, along
           with new helper functions. Some helpers are occasionally made
           available for additional program types. So in spite of the efforts
           of the community, this page might not be up-to-date. If you want
           to check by yourself what helper functions exist in your kernel,
           or what types of programs they can support, here are some files
           among the kernel tree that you may be interested in:
    
           • _include/uapi/linux/bpf.h_ is the main BPF header. It contains the
             full list of all helper functions, as well as many other BPF
             definitions including most of the flags, structs or constants
             used by the helpers.
    
           • _net/core/filter.c_ contains the definition of most
             network-related helper functions, and the list of program types
             from which they can be used.
    
           • _kernel/trace/bpf_trace.c_ is the equivalent for most tracing
             program-related helpers.
    
           • _kernel/bpf/verifier.c_ contains the functions used to check that
             valid types of eBPF maps are used with a given helper function.
    
           • _kernel/bpf/_ directory contains other files in which additional
             helpers are defined (for cgroups, sockmaps, etc.).
    
           • The bpftool utility can be used to probe the availability of
             helper functions on the system (as well as supported program and
             map types, and a number of other parameters). To do so, run
             **bpftool feature probe**(see **bpftool-feature**(8) for details). Add
             the **unprivileged** keyword to list features available to
             unprivileged users.
    
           Compatibility between helper functions and program types can
           generally be found in the files where helper functions are
           defined. Look for the **struct bpf_func_proto** objects and for
           functions returning them: these functions contain a list of
           helpers that a given program type can call. Note that the **default:**
           label of the **switch ... case** used to filter helpers can call other
           functions, themselves allowing access to additional helpers. The
           requirement for GPL license is also in those **struct**
           **bpf_func_proto**.
    
           Compatibility between helper functions and map types can be found
           in the **check_map_func_compatibility**() function in file
           _kernel/bpf/verifier.c_.
    
           Helper functions that invalidate the checks on **data** and **data_end**
           pointers for network processing are listed in function
           **bpf_helper_changes_pkt_data**() in file _net/core/filter.c_.
    


* * *