# ibv_wr_rdma_read

## NAME



           ibv_wr_abort, ibv_wr_complete, ibv_wr_start - Manage regions
           allowed to post work
    
           ibv_wr_atomic_cmp_swp, ibv_wr_atomic_fetch_add - Post remote
           atomic operation work requests
    
           ibv_wr_bind_mw, ibv_wr_local_inv - Post work requests for memory
           windows
    
           ibv_wr_rdma_read, ibv_wr_rdma_write, ibv_wr_rdma_write_imm,
           ibv_wr_flush - Post RDMA work requests
    
           ibv_wr_send, ibv_wr_send_imm, ibv_wr_send_inv - Post send work
           requests
    
           ibv_wr_send_tso - Post segmentation offload work requests
    
           ibv_wr_set_inline_data, ibv_wr_set_inline_data_list - Attach
           inline data to the last work request
    
           ibv_wr_set_sge, ibv_wr_set_sge_list - Attach data to the last work
           request
    
           ibv_wr_set_ud_addr - Attach UD addressing info to the last work
           request
    
           ibv_wr_set_xrc_srqn - Attach an XRC SRQN to the last work request
    


## SYNOPSIS



                  #include <infiniband/verbs.h>
    
                  void ibv_wr_abort(struct ibv_qp_ex *qp);
                  int ibv_wr_complete(struct ibv_qp_ex *qp);
                  void ibv_wr_start(struct ibv_qp_ex *qp);
    
                  void ibv_wr_atomic_cmp_swp(struct ibv_qp_ex *qp, uint32_t rkey,
                                             uint64_t remote_addr, uint64_t compare,
                                             uint64_t swap);
                  void ibv_wr_atomic_fetch_add(struct ibv_qp_ex *qp, uint32_t rkey,
                                               uint64_t remote_addr, uint64_t add);
    
                  void ibv_wr_bind_mw(struct ibv_qp_ex *qp, struct ibv_mw *mw, uint32_t rkey,
                                      const struct ibv_mw_bind_info *bind_info);
                  void ibv_wr_local_inv(struct ibv_qp_ex *qp, uint32_t invalidate_rkey);
    
                  void ibv_wr_rdma_read(struct ibv_qp_ex *qp, uint32_t rkey,
                                        uint64_t remote_addr);
                  void ibv_wr_rdma_write(struct ibv_qp_ex *qp, uint32_t rkey,
                                         uint64_t remote_addr);
                  void ibv_wr_rdma_write_imm(struct ibv_qp_ex *qp, uint32_t rkey,
                                             uint64_t remote_addr, __be32 imm_data);
    
                  void ibv_wr_send(struct ibv_qp_ex *qp);
                  void ibv_wr_send_imm(struct ibv_qp_ex *qp, __be32 imm_data);
                  void ibv_wr_send_inv(struct ibv_qp_ex *qp, uint32_t invalidate_rkey);
                  void ibv_wr_send_tso(struct ibv_qp_ex *qp, void *hdr, uint16_t hdr_sz,
                                       uint16_t mss);
    
                  void ibv_wr_set_inline_data(struct ibv_qp_ex *qp, void *addr, size_t length);
                  void ibv_wr_set_inline_data_list(struct ibv_qp_ex *qp, size_t num_buf,
                                                   const struct ibv_data_buf *buf_list);
                  void ibv_wr_set_sge(struct ibv_qp_ex *qp, uint32_t lkey, uint64_t addr,
                                      uint32_t length);
                  void ibv_wr_set_sge_list(struct ibv_qp_ex *qp, size_t num_sge,
                                           const struct ibv_sge *sg_list);
    
                  void ibv_wr_set_ud_addr(struct ibv_qp_ex *qp, struct ibv_ah *ah,
                                          uint32_t remote_qpn, uint32_t remote_qkey);
                  void ibv_wr_set_xrc_srqn(struct ibv_qp_ex *qp, uint32_t remote_srqn);
                  void ibv_wr_flush(struct ibv_qp_ex *qp, uint32_t rkey, uint64_t remote_addr,
                                    size_t len, uint8_t type, uint8_t level);
    


## DESCRIPTION



           The verbs work request API (ibv_wr_*) allows efficient posting of
           work to a send queue using function calls instead of the struct
           based _ibv_post_send()_ scheme.  This approach is designed to
           minimize CPU branching and locking during the posting process.
    
           This API is intended to be used to access additional functionality
           beyond what is provided by _ibv_post_send()_.
    
           WRs batches of _ibv_post_send()_ and this API WRs batches can
           interleave together just if they are not posted within the
           critical region of each other.  (A critical region in this API
           formed by _ibv_wr_start()_ and _ibv_wr_complete()_ /_ibv_wr_abort()_)
    


## USAGE



           To use these APIs the QP must be created using ibv_create_qp_ex()
           which allows setting the **IBV_QP_INIT_ATTR_SEND_OPS_FLAGS** in
           _comp_mask_.  The _send_ops_flags_ should be set to the OR of the work
           request types that will be posted to the QP.
    
           If the QP does not support all the requested work request types
           then QP creation will fail.
    
           Posting work requests to the QP is done within the critical region
           formed by _ibv_wr_start()_ and _ibv_wr_complete()_ /_ibv_wr_abort()_ (see
           CONCURRENCY below).
    
           Each work request is created by calling a WR builder function (see
           the table column WR builder below) to start creating the work
           request, followed by allowed/required setter functions described
           below.
    
           The WR builder and setter combination can be called multiple times
           to efficiently post multiple work requests within a single
           critical region.
    
           Each WR builder will use the _wr_id_ member of _struct ibv_qp_ex_ to
           set the value to be returned in the completion.  Some operations
           will also use the _wr_flags_ member to influence operation (see
           Flags below).  These values should be set before invoking the WR
           builder function.
    
           For example a simple send could be formed as follows:
    
                  qpx->wr_id = 1;
                  ibv_wr_send(qpx);
                  ibv_wr_set_sge(qpx, lkey, &data, sizeof(data));
    
           The section WORK REQUESTS describes the various WR builders and
           setters in details.
    
           Posting work is completed by calling _ibv_wr_complete()_ or
           _ibv_wr_abort()_.  No work is executed to the queue until
           _ibv_wr_complete()_ returns success.  _ibv_wr_abort()_ will discard
           all work prepared since _ibv_wr_start()_.
    


## WORK REQUESTS



           Many of the operations match the opcodes available for
           _ibv_post_send()_.  Each operation has a WR builder function, a list
           of allowed setters, and a flag bit to request the operation with
           _send_ops_flags_ in _struct ibv_qp_init_attr_ex_ (see the EXAMPLE
           below).
    
           Operation              WR builder                  QP Type Supported            setters
           ────────────────────────────────────────────────────────────────────────────────────────
           ATOMIC_CMP_AND_SWP     ibv_wr_atomic_cmp_swp()     RC, XRC_SEND                 DATA,
                                                                                           QP
           ATOMIC_FETCH_AND_ADD   ibv_wr_atomic_fetch_add()   RC, XRC_SEND                 DATA,
                                                                                           QP
           BIND_MW                ibv_wr_bind_mw()            UC, RC, XRC_SEND             NONE
           LOCAL_INV              ibv_wr_local_inv()          UC, RC, XRC_SEND             NONE
           RDMA_READ              ibv_wr_rdma_read()          RC, XRC_SEND                 DATA,
                                                                                           QP
           RDMA_WRITE             ibv_wr_rdma_write()         UC, RC, XRC_SEND             DATA,
                                                                                           QP
           FLUSH                  ibv_wr_flush()              RC, RD, XRC_SEND             DATA,
                                                                                           QP
           RDMA_WRITE_WITH_IMM    ibv_wr_rdma_write_imm()     UC, RC, XRC_SEND             DATA,
                                                                                           QP
           SEND                   ibv_wr_send()               UD, UC, RC, XRC_SEND,        DATA,
                                                              RAW_PACKET                   QP
           SEND_WITH_IMM          ibv_wr_send_imm()           UD, UC, RC, SRC SEND         DATA,
                                                                                           QP
           SEND_WITH_INV          ibv_wr_send_inv()           UC, RC, XRC_SEND             DATA,
                                                                                           QP
           TSO                    ibv_wr_send_tso()           UD, RAW_PACKET               DATA,
                                                                                           QP
    
       **Atomic operations**
           Atomic operations are only atomic so long as all writes to memory
           go only through the same RDMA hardware.  It is not atomic with
           writes performed by the CPU, or by other RDMA hardware in the
           system.
    
           _ibv_wr_atomic_cmp_swp()_
                  If the remote 64 bit memory location specified by _rkey_ and
                  _remote_addr_ equals _compare_ then set it to _swap_.
    
           _ibv_wr_atomic_fetch_add()_
                  Add _add_ to the 64 bit memory location specified _rkey_ and
                  _remote_addr_.
    
       **Memory Windows**
           Memory window type 2 operations (See man page for ibv_alloc_mw).
    
           _ibv_wr_bind_mw()_
                  Bind a MW type 2 specified by **mw** , set a new **rkey** and set
                  its properties by **bind_info**.
    
           _ibv_wr_local_inv()_
                  Invalidate a MW type 2 which is associated with **rkey**.
    
       **RDMA**
           _ibv_wr_rdma_read()_
                  Read from the remote memory location specified _rkey_ and
                  _remote_addr_.  The number of bytes to read, and the local
                  location to store the data, is determined by the DATA
                  buffers set after this call.
    
           _ibv_wr_rdma_write()_ , _ibv_wr_rdma_write_imm()_
                  Write to the remote memory location specified _rkey_ and
                  _remote_addr_.  The number of bytes to read, and the local
                  location to get the data, is determined by the DATA buffers
                  set after this call.
    
                  The _imm version causes the remote side to get a
                  IBV_WC_RECV_RDMA_WITH_IMM containing the 32 bits of
                  immediate data.
    
       **Message Send**
           _ibv_wr_send()_ , _ibv_wr_send_imm()_
                  Send a message.  The number of bytes to send, and the local
                  location to get the data, is determined by the DATA buffers
                  set after this call.
    
                  The _imm version causes the remote side to get a
                  IBV_WC_RECV_RDMA_WITH_IMM containing the 32 bits of
                  immediate data.
    
           _ibv_wr_send_inv()_
                  The data transfer is the same as for _ibv_wr_send()_ , however
                  the remote side will invalidate the MR specified by
                  _invalidate_rkey_ before delivering a completion.
    
           _ibv_wr_send_tso()_
                  Produce multiple SEND messages using TCP Segmentation
                  Offload.  The SGE points to a TCP Stream buffer which will
                  be segmented into MSS size SENDs.  The hdr includes the
                  entire network headers up to and including the TCP header
                  and is prefixed before each segment.
    
       **QP Specific setters**
           Certain QP types require each post to be accompanied by additional
           setters, these setters are mandatory for any operation listing a
           QP setter in the above table.
    
           _UD_ QPs _ibv_wr_set_ud_addr()_ must be called to set the destination
                  address of the work.
    
           _XRC_SEND_ QPs
                  _ibv_wr_set_xrc_srqn()_ must be called to set the destination
                  SRQN field.
    
       **DATA transfer setters**
           For work that requires to transfer data one of the following
           setters should be called once after the WR builder:
    
           _ibv_wr_set_sge()_
                  Transfer data to/from a single buffer given by the lkey,
                  addr and length.  This is equivalent to
                  _ibv_wr_set_sge_list()_ with a single element.
    
           _ibv_wr_set_sge_list()_
                  Transfer data to/from a list of buffers, logically
                  concatenated together.  Each buffer is specified by an
                  element in an array of _struct ibv_sge_.
    
           Inline setters will copy the send data during the setter and
           allows the caller to immediately re-use the buffer.  This behavior
           is identical to the IBV_SEND_INLINE flag.  Generally this copy is
           done in a way that optimizes SEND latency and is suitable for
           small messages.  The provider will limit the amount of data it can
           support in a single operation.  This limit is requested in the
           _max_inline_data_ member of _struct ibv_qp_init_attr_.  Valid only for
           SEND and RDMA_WRITE.
    
           _ibv_wr_set_inline_data()_
                  Copy send data from a single buffer given by the addr and
                  length.  This is equivalent to
                  _ibv_wr_set_inline_data_list()_ with a single element.
    
           _ibv_wr_set_inline_data_list()_
                  Copy send data from a list of buffers, logically
                  concatenated together.  Each buffer is specified by an
                  element in an array of _struct ibv_inl_data_.
    
       **Flags**
           A bit mask of flags may be specified in _wr_flags_ to control the
           behavior of the work request.
    
           **IBV_SEND_FENCE**
                  Do not start this work request until prior work has
                  completed.
    
           **IBV_SEND_IP_CSUM**
                  Offload the IPv4 and TCP/UDP checksum calculation
    
           **IBV_SEND_SIGNALED**
                  A completion will be generated in the completion queue for
                  the operation.
    
           **IBV_SEND_SOLICITED**
                  Set the solicited bit in the RDMA packet.  This informs the
                  other side to generate a completion event upon receiving
                  the RDMA operation.
    


## CONCURRENCY



           The provider will provide locking to ensure that _ibv_wr_start()_
           and _ibv_wr_complete()/abort()_ form a per-QP critical section where
           no other threads can enter.
    
           If an _ibv_td_ is provided during QP creation then no locking will
           be performed and it is up to the caller to ensure that only one
           thread can be within the critical region at a time.
    


## RETURN VALUE



           Applications should use this API in a way that does not create
           failures.  The individual APIs do not return a failure indication
           to avoid branching.
    
           If a failure is detected during operation, for instance due to an
           invalid argument, then _ibv_wr_complete()_ will return failure and
           the entire posting will be aborted.
    


## EXAMPLE



                  /* create RC QP type and specify the required send opcodes */
                  qp_init_attr_ex.qp_type = IBV_QPT_RC;
                  qp_init_attr_ex.comp_mask |= IBV_QP_INIT_ATTR_SEND_OPS_FLAGS;
                  qp_init_attr_ex.send_ops_flags |= IBV_QP_EX_WITH_RDMA_WRITE;
                  qp_init_attr_ex.send_ops_flags |= IBV_QP_EX_WITH_RDMA_WRITE_WITH_IMM;
    
                  ibv_qp *qp = ibv_create_qp_ex(ctx, qp_init_attr_ex);
                  ibv_qp_ex *qpx = ibv_qp_to_qp_ex(qp);
    
                  ibv_wr_start(qpx);
    
                  /* create 1st WRITE WR entry */
                  qpx->wr_id = my_wr_id_1;
                  ibv_wr_rdma_write(qpx, rkey, remote_addr_1);
                  ibv_wr_set_sge(qpx, lkey, local_addr_1, length_1);
    
                  /* create 2nd WRITE_WITH_IMM WR entry */
                  qpx->wr_id = my_wr_id_2;
                  qpx->wr_flags = IBV_SEND_SIGNALED;
                  ibv_wr_rdma_write_imm(qpx, rkey, remote_addr_2, htonl(0x1234));
                  ibv_set_wr_sge(qpx, lkey, local_addr_2, length_2);
    
                  /* Begin processing WRs */
                  ret = ibv_wr_complete(qpx);
    


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