text: /******************************************************************************
   * netif.h
   *
   * Unified network-device I/O interface for Xen guest OSes.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to
   * deal in the Software without restriction, including without limitation the
   * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
   * sell copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   * DEALINGS IN THE SOFTWARE.
   *
   * Copyright (c) 2003-2004, Keir Fraser
   */
  
  #ifndef __XEN_PUBLIC_IO_NETIF_H__
  #define __XEN_PUBLIC_IO_NETIF_H__
  
  #include "ring.h"
  #include "../grant_table.h"
  
  /*
   * Older implementation of Xen network frontend / backend has an
   * implicit dependency on the MAX_SKB_FRAGS as the maximum number of
   * ring slots a skb can use. Netfront / netback may not work as
   * expected when frontend and backend have different MAX_SKB_FRAGS.
   *
   * A better approach is to add mechanism for netfront / netback to
   * negotiate this value. However we cannot fix all possible
   * frontends, so we need to define a value which states the minimum
   * slots backend must support.
   *
   * The minimum value derives from older Linux kernel's MAX_SKB_FRAGS
   * (18), which is proved to work with most frontends. Any new backend
   * which doesn't negotiate with frontend should expect frontend to
   * send a valid packet using slots up to this value.
   */
  #define XEN_NETIF_NR_SLOTS_MIN 18
  
  /*
   * Notifications after enqueuing any type of message should be conditional on
   * the appropriate req_event or rsp_event field in the shared ring.
   * If the client sends notification for rx requests then it should specify
   * feature 'feature-rx-notify' via xenbus. Otherwise the backend will assume
   * that it cannot safely queue packets (as it may not be kicked to send them).
   */
  
  /*
   * "feature-split-event-channels" is introduced to separate guest TX
   * and RX notification. Backend either doesn't support this feature or
   * advertises it via xenstore as 0 (disabled) or 1 (enabled).
   *
   * To make use of this feature, frontend should allocate two event
   * channels for TX and RX, advertise them to backend as
   * "event-channel-tx" and "event-channel-rx" respectively. If frontend
   * doesn't want to use this feature, it just writes "event-channel"
   * node as before.
   */
  
  /*
   * Multiple transmit and receive queues:
   * If supported, the backend will write the key "multi-queue-max-queues" to
   * the directory for that vif, and set its value to the maximum supported
   * number of queues.
   * Frontends that are aware of this feature and wish to use it can write the
   * key "multi-queue-num-queues", set to the number they wish to use, which
   * must be greater than zero, and no more than the value reported by the backend
   * in "multi-queue-max-queues".
   *
   * Queues replicate the shared rings and event channels.
   * "feature-split-event-channels" may optionally be used when using
   * multiple queues, but is not mandatory.
   *
   * Each queue consists of one shared ring pair, i.e. there must be the same
   * number of tx and rx rings.
   *
   * For frontends requesting just one queue, the usual event-channel and
   * ring-ref keys are written as before, simplifying the backend processing
   * to avoid distinguishing between a frontend that doesn't understand the
   * multi-queue feature, and one that does, but requested only one queue.
   *
   * Frontends requesting two or more queues must not write the toplevel
   * event-channel (or event-channel-{tx,rx}) and {tx,rx}-ring-ref keys,
   * instead writing those keys under sub-keys having the name "queue-N" where
   * N is the integer ID of the queue for which those keys belong. Queues
   * are indexed from zero. For example, a frontend with two queues and split
   * event channels must write the following set of queue-related keys:
   *
   * /local/domain/1/device/vif/0/multi-queue-num-queues = "2"
   * /local/domain/1/device/vif/0/queue-0 = ""
   * /local/domain/1/device/vif/0/queue-0/tx-ring-ref = "<ring-ref-tx0>"
   * /local/domain/1/device/vif/0/queue-0/rx-ring-ref = "<ring-ref-rx0>"
   * /local/domain/1/device/vif/0/queue-0/event-channel-tx = "<evtchn-tx0>"
   * /local/domain/1/device/vif/0/queue-0/event-channel-rx = "<evtchn-rx0>"
   * /local/domain/1/device/vif/0/queue-1 = ""
   * /local/domain/1/device/vif/0/queue-1/tx-ring-ref = "<ring-ref-tx1>"
   * /local/domain/1/device/vif/0/queue-1/rx-ring-ref = "<ring-ref-rx1"
   * /local/domain/1/device/vif/0/queue-1/event-channel-tx = "<evtchn-tx1>"
   * /local/domain/1/device/vif/0/queue-1/event-channel-rx = "<evtchn-rx1>"
   *
   * If there is any inconsistency in the XenStore data, the backend may
   * choose not to connect any queues, instead treating the request as an
   * error. This includes scenarios where more (or fewer) queues were
   * requested than the frontend provided details for.
   *
   * Mapping of packets to queues is considered to be a function of the
   * transmitting system (backend or frontend) and is not negotiated
   * between the two. Guests are free to transmit packets on any queue
   * they choose, provided it has been set up correctly. Guests must be
   * prepared to receive packets on any queue they have requested be set up.
   */
  
  /*
   * "feature-no-csum-offload" should be used to turn IPv4 TCP/UDP checksum
   * offload off or on. If it is missing then the feature is assumed to be on.
   * "feature-ipv6-csum-offload" should be used to turn IPv6 TCP/UDP checksum
   * offload on or off. If it is missing then the feature is assumed to be off.
   */
  
  /*
   * "feature-gso-tcpv4" and "feature-gso-tcpv6" advertise the capability to
   * handle large TCP packets (in IPv4 or IPv6 form respectively). Neither
   * frontends nor backends are assumed to be capable unless the flags are
   * present.
   */
  
  /*
   * "feature-multicast-control" and "feature-dynamic-multicast-control"
   * advertise the capability to filter ethernet multicast packets in the
   * backend. If the frontend wishes to take advantage of this feature then
   * it may set "request-multicast-control". If the backend only advertises
   * "feature-multicast-control" then "request-multicast-control" must be set
   * before the frontend moves into the connected state. The backend will
   * sample the value on this state transition and any subsequent change in
   * value will have no effect. However, if the backend also advertises
   * "feature-dynamic-multicast-control" then "request-multicast-control"
   * may be set by the frontend at any time. In this case, the backend will
   * watch the value and re-sample on watch events.
   *
   * If the sampled value of "request-multicast-control" is set then the
   * backend transmit side should no longer flood multicast packets to the
   * frontend, it should instead drop any multicast packet that does not
   * match in a filter list.
   * The list is amended by the frontend by sending dummy transmit requests
   * containing XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL} extra-info fragments as
   * specified below.
   * Note that the filter list may be amended even if the sampled value of
   * "request-multicast-control" is not set, however the filter should only
   * be applied if it is set.
   */
  
  /*
   * Control ring
   * ============
   *
   * Some features, such as hashing (detailed below), require a
   * significant amount of out-of-band data to be passed from frontend to
   * backend. Use of xenstore is not suitable for large quantities of data
   * because of quota limitations and so a dedicated 'control ring' is used.
   * The ability of the backend to use a control ring is advertised by
   * setting:
   *
   * /local/domain/X/backend/<domid>/<vif>/feature-ctrl-ring = "1"
   *
   * The frontend provides a control ring to the backend by setting:
   *
   * /local/domain/<domid>/device/vif/<vif>/ctrl-ring-ref = <gref>
   * /local/domain/<domid>/device/vif/<vif>/event-channel-ctrl = <port>
   *
   * where <gref> is the grant reference of the shared page used to
   * implement the control ring and <port> is an event channel to be used
   * as a mailbox interrupt. These keys must be set before the frontend
   * moves into the connected state.
   *
   * The control ring uses a fixed request/response message size and is
   * balanced (i.e. one request to one response), so operationally it is much
   * the same as a transmit or receive ring.
   * Note that there is no requirement that responses are issued in the same
   * order as requests.
   */
  
  /*
   * Hash types
   * ==========
   *
   * For the purposes of the definitions below, 'Packet[]' is an array of
   * octets containing an IP packet without options, 'Array[X..Y]' means a
   * sub-array of 'Array' containing bytes X thru Y inclusive, and '+' is
   * used to indicate concatenation of arrays.
   */
  
  /*
   * A hash calculated over an IP version 4 header as follows:
   *
   * Buffer[0..8] = Packet[12..15] (source address) +
   *                Packet[16..19] (destination address)
   *
   * Result = Hash(Buffer, 8)
   */
  #define _XEN_NETIF_CTRL_HASH_TYPE_IPV4 0
  #define XEN_NETIF_CTRL_HASH_TYPE_IPV4 \
      (1 << _XEN_NETIF_CTRL_HASH_TYPE_IPV4)
  
  /*
   * A hash calculated over an IP version 4 header and TCP header as
   * follows:
   *
   * Buffer[0..12] = Packet[12..15] (source address) +
   *                 Packet[16..19] (destination address) +
   *                 Packet[20..21] (source port) +
   *                 Packet[22..23] (destination port)
   *
   * Result = Hash(Buffer, 12)
   */
  #define _XEN_NETIF_CTRL_HASH_TYPE_IPV4_TCP 1
  #define XEN_NETIF_CTRL_HASH_TYPE_IPV4_TCP \
      (1 << _XEN_NETIF_CTRL_HASH_TYPE_IPV4_TCP)
  
  /*
   * A hash calculated over an IP version 6 header as follows:
   *
   * Buffer[0..32] = Packet[8..23]  (source address ) +
   *                 Packet[24..39] (destination address)
   *
   * Result = Hash(Buffer, 32)
   */
  #define _XEN_NETIF_CTRL_HASH_TYPE_IPV6 2
  #define XEN_NETIF_CTRL_HASH_TYPE_IPV6 \
      (1 << _XEN_NETIF_CTRL_HASH_TYPE_IPV6)
  
  /*
   * A hash calculated over an IP version 6 header and TCP header as
   * follows:
   *
   * Buffer[0..36] = Packet[8..23]  (source address) +
   *                 Packet[24..39] (destination address) +
   *                 Packet[40..41] (source port) +
   *                 Packet[42..43] (destination port)
   *
   * Result = Hash(Buffer, 36)
   */
  #define _XEN_NETIF_CTRL_HASH_TYPE_IPV6_TCP 3
  #define XEN_NETIF_CTRL_HASH_TYPE_IPV6_TCP \
      (1 << _XEN_NETIF_CTRL_HASH_TYPE_IPV6_TCP)
  
  /*
   * Hash algorithms
   * ===============
   */
  
  #define XEN_NETIF_CTRL_HASH_ALGORITHM_NONE 0
  
  /*
   * Toeplitz hash:
   */
  
  #define XEN_NETIF_CTRL_HASH_ALGORITHM_TOEPLITZ 1
  
  /*
   * Control requests (struct xen_netif_ctrl_request)
   * ================================================
   *
   * All requests have the following format:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |    id     |   type    |         data[0]       |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |         data[1]       |         data[2]       |
   * +-----+-----+-----+-----+-----------------------+
   *
   * id: the request identifier, echoed in response.
   * type: the type of request (see below)
   * data[]: any data associated with the request (determined by type)
   */
  
  struct xen_netif_ctrl_request {
      uint16_t id;
      uint16_t type;
  
  #define XEN_NETIF_CTRL_TYPE_INVALID               0
  #define XEN_NETIF_CTRL_TYPE_GET_HASH_FLAGS        1
  #define XEN_NETIF_CTRL_TYPE_SET_HASH_FLAGS        2
  #define XEN_NETIF_CTRL_TYPE_SET_HASH_KEY          3
  #define XEN_NETIF_CTRL_TYPE_GET_HASH_MAPPING_SIZE 4
  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING      6
  #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM    7
  #define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
  #define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING      9
  #define XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING     10
  
      uint32_t data[3];
  };
  
  /*
   * Control responses (struct xen_netif_ctrl_response)
   * ==================================================
   *
   * All responses have the following format:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |    id     |   type    |         status        |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |         data          |
   * +-----+-----+-----+-----+
   *
   * id: the corresponding request identifier
   * type: the type of the corresponding request
   * status: the status of request processing
   * data: any data associated with the response (determined by type and
   *       status)
   */
  
  struct xen_netif_ctrl_response {
      uint16_t id;
      uint16_t type;
      uint32_t status;
  
  #define XEN_NETIF_CTRL_STATUS_SUCCESS           0
  #define XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     1
  #define XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER 2
  #define XEN_NETIF_CTRL_STATUS_BUFFER_OVERFLOW   3
  
      uint32_t data;
  };
  
  /*
   * Static Grants (struct xen_netif_gref)
   * =====================================
   *
   * A frontend may provide a fixed set of grant references to be mapped on
   * the backend. The message of type XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
   * prior its usage in the command ring allows for creation of these mappings.
   * The backend will maintain a fixed amount of these mappings.
   *
   * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend query how many
   * of these mappings can be kept.
   *
   * Each entry in the XEN_NETIF_CTRL_TYPE_{ADD,DEL}_GREF_MAPPING input table has
   * the following format:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | grant ref             |  flags    |  status   |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * grant ref: grant reference (IN)
   * flags: flags describing the control operation (IN)
   * status: XEN_NETIF_CTRL_STATUS_* (OUT)
   *
   * 'status' is an output parameter which does not require to be set to zero
   * prior to its usage in the corresponding control messages.
   */
  
  struct xen_netif_gref {
         grant_ref_t ref;
         uint16_t flags;
  
  #define _XEN_NETIF_CTRLF_GREF_readonly    0
  #define XEN_NETIF_CTRLF_GREF_readonly    (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
  
         uint16_t status;
  };
  
  /*
   * Control messages
   * ================
   *
   * XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM
   * --------------------------------------
   *
   * This is sent by the frontend to set the desired hash algorithm.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM
   *  data[0] = a XEN_NETIF_CTRL_HASH_ALGORITHM_* value
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The algorithm is not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *
   * NOTE: Setting data[0] to XEN_NETIF_CTRL_HASH_ALGORITHM_NONE disables
   *       hashing and the backend is free to choose how it steers packets
   *       to queues (which is the default behaviour).
   *
   * XEN_NETIF_CTRL_TYPE_GET_HASH_FLAGS
   * ----------------------------------
   *
   * This is sent by the frontend to query the types of hash supported by
   * the backend.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_GET_HASH_FLAGS
   *  data[0] = 0
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not supported
   *           XEN_NETIF_CTRL_STATUS_SUCCESS       - Operation successful
   *  data   = supported hash types (if operation was successful)
   *
   * NOTE: A valid hash algorithm must be selected before this operation can
   *       succeed.
   *
   * XEN_NETIF_CTRL_TYPE_SET_HASH_FLAGS
   * ----------------------------------
   *
   * This is sent by the frontend to set the types of hash that the backend
   * should calculate. (See above for hash type definitions).
   * Note that the 'maximal' type of hash should always be chosen. For
   * example, if the frontend sets both IPV4 and IPV4_TCP hash types then
   * the latter hash type should be calculated for any TCP packet and the
   * former only calculated for non-TCP packets.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_SET_HASH_FLAGS
   *  data[0] = bitwise OR of XEN_NETIF_CTRL_HASH_TYPE_* values
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - One or more flag
   *                                                     value is invalid or
   *                                                     unsupported
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = 0
   *
   * NOTE: A valid hash algorithm must be selected before this operation can
   *       succeed.
   *       Also, setting data[0] to zero disables hashing and the backend
   *       is free to choose how it steers packets to queues.
   *
   * XEN_NETIF_CTRL_TYPE_SET_HASH_KEY
   * --------------------------------
   *
   * This is sent by the frontend to set the key of the hash if the algorithm
   * requires it. (See hash algorithms above).
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_SET_HASH_KEY
   *  data[0] = grant reference of page containing the key (assumed to
   *            start at beginning of grant)
   *  data[1] = size of key in octets
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Key size is invalid
   *           XEN_NETIF_CTRL_STATUS_BUFFER_OVERFLOW   - Key size is larger
   *                                                     than the backend
   *                                                     supports
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = 0
   *
   * NOTE: Any key octets not specified are assumed to be zero (the key
   *       is assumed to be empty by default) and specifying a new key
   *       invalidates any previous key, hence specifying a key size of
   *       zero will clear the key (which ensures that the calculated hash
   *       will always be zero).
   *       The maximum size of key is algorithm and backend specific, but
   *       is also limited by the single grant reference.
   *       The grant reference may be read-only and must remain valid until
   *       the response has been processed.
   *
   * XEN_NETIF_CTRL_TYPE_GET_HASH_MAPPING_SIZE
   * -----------------------------------------
   *
   * This is sent by the frontend to query the maximum size of mapping
   * table supported by the backend. The size is specified in terms of
   * table entries.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_GET_HASH_MAPPING_SIZE
   *  data[0] = 0
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not supported
   *           XEN_NETIF_CTRL_STATUS_SUCCESS       - Operation successful
   *  data   = maximum number of entries allowed in the mapping table
   *           (if operation was successful) or zero if a mapping table is
   *           not supported (i.e. hash mapping is done only by modular
   *           arithmetic).
   *
   * XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE
   * -------------------------------------
   *
   * This is sent by the frontend to set the actual size of the mapping
   * table to be used by the backend. The size is specified in terms of
   * table entries.
   * Any previous table is invalidated by this message and any new table
   * is assumed to be zero filled.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE
   *  data[0] = number of entries in mapping table
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Table size is invalid
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = 0
   *
   * NOTE: Setting data[0] to 0 means that hash mapping should be done
   *       using modular arithmetic.
   *
   * XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING
   * ------------------------------------
   *
   * This is sent by the frontend to set the content of the table mapping
   * hash value to queue number. The backend should calculate the hash from
   * the packet header, use it as an index into the table (modulo the size
   * of the table) and then steer the packet to the queue number found at
   * that index.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING
   *  data[0] = grant reference of page containing the mapping (sub-)table
   *            (assumed to start at beginning of grant)
   *  data[1] = size of (sub-)table in entries
   *  data[2] = offset, in entries, of sub-table within overall table
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Table size or content
   *                                                     is invalid
   *           XEN_NETIF_CTRL_STATUS_BUFFER_OVERFLOW   - Table size is larger
   *                                                     than the backend
   *                                                     supports
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = 0
   *
   * NOTE: The overall table has the following format:
   *
   *          0     1     2     3     4     5     6     7  octet
   *       +-----+-----+-----+-----+-----+-----+-----+-----+
   *       |       mapping[0]      |       mapping[1]      |
   *       +-----+-----+-----+-----+-----+-----+-----+-----+
   *       |                       .                       |
   *       |                       .                       |
   *       |                       .                       |
   *       +-----+-----+-----+-----+-----+-----+-----+-----+
   *       |      mapping[N-2]     |      mapping[N-1]     |
   *       +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   *       where N is specified by a XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE
   *       message and each  mapping must specifies a queue between 0 and
   *       "multi-queue-num-queues" (see above).
   *       The backend may support a mapping table larger than can be
   *       mapped by a single grant reference. Thus sub-tables within a
   *       larger table can be individually set by sending multiple messages
   *       with differing offset values. Specifying a new sub-table does not
   *       invalidate any table data outside that range.
   *       The grant reference may be read-only and must remain valid until
   *       the response has been processed.
   *
   * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
   * -----------------------------------------
   *
   * This is sent by the frontend to fetch the number of grefs that can be kept
   * mapped in the backend.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
   *  data[0] = queue index (assumed 0 for single queue)
   *  data[1] = 0
   *  data[2] = 0
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The queue index is
   *                                                     out of range
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = maximum number of entries allowed in the gref mapping table
   *           (if operation was successful) or zero if it is not supported.
   *
   * XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
   * ------------------------------------
   *
   * This is sent by the frontend for backend to map a list of grant
   * references.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
   *  data[0] = queue index
   *  data[1] = grant reference of page containing the mapping list
   *            (r/w and assumed to start at beginning of page)
   *  data[2] = size of list in entries
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Operation failed
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *
   * NOTE: Each entry in the input table has the format outlined
   *       in struct xen_netif_gref.
   *       Contrary to XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING, the struct
   *       xen_netif_gref 'status' field is not used and therefore the response
   *       'status' determines the success of this operation. In case of
   *       failure none of grants mappings get added in the backend.
   *
   * XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING
   * ------------------------------------
   *
   * This is sent by the frontend for backend to unmap a list of grant
   * references.
   *
   * Request:
   *
   *  type    = XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING
   *  data[0] = queue index
   *  data[1] = grant reference of page containing the mapping list
   *            (r/w and assumed to start at beginning of page)
   *  data[2] = size of list in entries
   *
   * Response:
   *
   *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED     - Operation not
   *                                                     supported
   *           XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Operation failed
   *           XEN_NETIF_CTRL_STATUS_SUCCESS           - Operation successful
   *  data   = number of entries that were unmapped
   *
   * NOTE: Each entry in the input table has the format outlined in struct
   *       xen_netif_gref.
   *       The struct xen_netif_gref 'status' field determines if the entry
   *       was successfully removed.
   *       The entries used are only the ones representing grant references that
   *       were previously the subject of a XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
   *       operation. Any other entries will have their status set to
   *       XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER upon completion.
   */
  
  DEFINE_RING_TYPES(xen_netif_ctrl,
                    struct xen_netif_ctrl_request,
                    struct xen_netif_ctrl_response);
  
  /*
   * Guest transmit
   * ==============
   *
   * This is the 'wire' format for transmit (frontend -> backend) packets:
   *
   *  Fragment 1: netif_tx_request_t  - flags = NETTXF_*
   *                                    size = total packet size
   * [Extra 1: netif_extra_info_t]    - (only if fragment 1 flags include
   *                                     NETTXF_extra_info)
   *  ...
   * [Extra N: netif_extra_info_t]    - (only if extra N-1 flags include
   *                                     XEN_NETIF_EXTRA_MORE)
   *  ...
   *  Fragment N: netif_tx_request_t  - (only if fragment N-1 flags include
   *                                     NETTXF_more_data - flags on preceding
   *                                     extras are not relevant here)
   *                                    flags = 0
   *                                    size = fragment size
   *
   * NOTE:
   *
   * This format slightly is different from that used for receive
   * (backend -> frontend) packets. Specifically, in a multi-fragment
   * packet the actual size of fragment 1 can only be determined by
   * subtracting the sizes of fragments 2..N from the total packet size.
   *
   * Ring slot size is 12 octets, however not all request/response
   * structs use the full size.
   *
   * tx request data (netif_tx_request_t)
   * ------------------------------------
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | grant ref             | offset    | flags     |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | id        | size      |
   * +-----+-----+-----+-----+
   *
   * grant ref: Reference to buffer page.
   * offset: Offset within buffer page.
   * flags: NETTXF_*.
   * id: request identifier, echoed in response.
   * size: packet size in bytes.
   *
   * tx response (netif_tx_response_t)
   * ---------------------------------
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | id        | status    | unused                |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | unused                |
   * +-----+-----+-----+-----+
   *
   * id: reflects id in transmit request
   * status: NETIF_RSP_*
   *
   * Guest receive
   * =============
   *
   * This is the 'wire' format for receive (backend -> frontend) packets:
   *
   *  Fragment 1: netif_rx_request_t  - flags = NETRXF_*
   *                                    size = fragment size
   * [Extra 1: netif_extra_info_t]    - (only if fragment 1 flags include
   *                                     NETRXF_extra_info)
   *  ...
   * [Extra N: netif_extra_info_t]    - (only if extra N-1 flags include
   *                                     XEN_NETIF_EXTRA_MORE)
   *  ...
   *  Fragment N: netif_rx_request_t  - (only if fragment N-1 flags include
   *                                     NETRXF_more_data - flags on preceding
   *                                     extras are not relevant here)
   *                                    flags = 0
   *                                    size = fragment size
   *
   * NOTE:
   *
   * This format slightly is different from that used for transmit
   * (frontend -> backend) packets. Specifically, in a multi-fragment
   * packet the size of the packet can only be determined by summing the
   * sizes of fragments 1..N.
   *
   * Ring slot size is 8 octets.
   *
   * rx request (netif_rx_request_t)
   * -------------------------------
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | id        | pad       | gref                  |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * id: request identifier, echoed in response.
   * gref: reference to incoming granted frame.
   *
   * rx response (netif_rx_response_t)
   * ---------------------------------
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | id        | offset    | flags     | status    |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * id: reflects id in receive request
   * offset: offset in page of start of received packet
   * flags: NETRXF_*
   * status: -ve: NETIF_RSP_*; +ve: Rx'ed pkt size.
   *
   * NOTE: Historically, to support GSO on the frontend receive side, Linux
   *       netfront does not make use of the rx response id (because, as
   *       described below, extra info structures overlay the id field).
   *       Instead it assumes that responses always appear in the same ring
   *       slot as their corresponding request. Thus, to maintain
   *       compatibility, backends must make sure this is the case.
   *
   * Extra Info
   * ==========
   *
   * Can be present if initial request or response has NET{T,R}XF_extra_info,
   * or previous extra request has XEN_NETIF_EXTRA_MORE.
   *
   * The struct therefore needs to fit into either a tx or rx slot and
   * is therefore limited to 8 octets.
   *
   * NOTE: Because extra info data overlays the usual request/response
   *       structures, there is no id information in the opposite direction.
   *       So, if an extra info overlays an rx response the frontend can
   *       assume that it is in the same ring slot as the request that was
   *       consumed to make the slot available, and the backend must ensure
   *       this assumption is true.
   *
   * extra info (netif_extra_info_t)
   * -------------------------------
   *
   * General format:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |type |flags| type specific data                |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * | padding for tx        |
   * +-----+-----+-----+-----+
   *
   * type: XEN_NETIF_EXTRA_TYPE_*
   * flags: XEN_NETIF_EXTRA_FLAG_*
   * padding for tx: present only in the tx case due to 8 octet limit
   *                 from rx case. Not shown in type specific entries
   *                 below.
   *
   * XEN_NETIF_EXTRA_TYPE_GSO:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |type |flags| size      |type | pad | features  |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * type: Must be XEN_NETIF_EXTRA_TYPE_GSO
   * flags: XEN_NETIF_EXTRA_FLAG_*
   * size: Maximum payload size of each segment. For example,
   *       for TCP this is just the path MSS.
   * type: XEN_NETIF_GSO_TYPE_*: This determines the protocol of
   *       the packet and any extra features required to segment the
   *       packet properly.
   * features: EN_NETIF_GSO_FEAT_*: This specifies any extra GSO
   *           features required to process this packet, such as ECN
   *           support for TCPv4.
   *
   * XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL}:
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |type |flags| addr                              |
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * type: Must be XEN_NETIF_EXTRA_TYPE_MCAST_{ADD,DEL}
   * flags: XEN_NETIF_EXTRA_FLAG_*
   * addr: address to add/remove
   *
   * XEN_NETIF_EXTRA_TYPE_HASH:
   *
   * A backend that supports teoplitz hashing is assumed to accept
   * this type of extra info in transmit packets.
   * A frontend that enables hashing is assumed to accept
   * this type of extra info in receive packets.
   *
   *    0     1     2     3     4     5     6     7  octet
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   * |type |flags|htype| alg |LSB ---- value ---- MSB|
   * +-----+-----+-----+-----+-----+-----+-----+-----+
   *
   * type: Must be XEN_NETIF_EXTRA_TYPE_HASH
   * flags: XEN_NETIF_EXTRA_FLAG_*
   * htype: Hash type (one of _XEN_NETIF_CTRL_HASH_TYPE_* - see above)
   * alg: The algorithm used to calculate the hash (one of
   *      XEN_NETIF_CTRL_HASH_TYPE_ALGORITHM_* - see above)
   * value: Hash value
   */
  
  /* Protocol checksum field is blank in the packet (hardware offload)? */
  #define _NETTXF_csum_blank     (0)
  #define  NETTXF_csum_blank     (1U<<_NETTXF_csum_blank)
  
  /* Packet data has been validated against protocol checksum. */
  #define _NETTXF_data_validated (1)
  #define  NETTXF_data_validated (1U<<_NETTXF_data_validated)
  
  /* Packet continues in the next request descriptor. */
  #define _NETTXF_more_data      (2)
  #define  NETTXF_more_data      (1U<<_NETTXF_more_data)
  
  /* Packet to be followed by extra descriptor(s). */
  #define _NETTXF_extra_info     (3)
  #define  NETTXF_extra_info     (1U<<_NETTXF_extra_info)
  
  #define XEN_NETIF_MAX_TX_SIZE 0xFFFF
  struct netif_tx_request {
      grant_ref_t gref;
      uint16_t offset;
      uint16_t flags;
      uint16_t id;
      uint16_t size;
  };
  typedef struct netif_tx_request netif_tx_request_t;
  
  /* Types of netif_extra_info descriptors. */
  #define XEN_NETIF_EXTRA_TYPE_NONE      (0)  /* Never used - invalid */
  #define XEN_NETIF_EXTRA_TYPE_GSO       (1)  /* u.gso */
  #define XEN_NETIF_EXTRA_TYPE_MCAST_ADD (2)  /* u.mcast */
  #define XEN_NETIF_EXTRA_TYPE_MCAST_DEL (3)  /* u.mcast */
  #define XEN_NETIF_EXTRA_TYPE_HASH      (4)  /* u.hash */
  #define XEN_NETIF_EXTRA_TYPE_MAX       (5)
  
  /* netif_extra_info_t flags. */
  #define _XEN_NETIF_EXTRA_FLAG_MORE (0)
  #define XEN_NETIF_EXTRA_FLAG_MORE  (1U<<_XEN_NETIF_EXTRA_FLAG_MORE)
  
  /* GSO types */
  #define XEN_NETIF_GSO_TYPE_NONE         (0)
  #define XEN_NETIF_GSO_TYPE_TCPV4        (1)
  #define XEN_NETIF_GSO_TYPE_TCPV6        (2)
  
  /*
   * This structure needs to fit within both netif_tx_request_t and
   * netif_rx_response_t for compatibility.
   */
  struct netif_extra_info {
      uint8_t type;
      uint8_t flags;
      union {
          struct {
              uint16_t size;
              uint8_t type;
              uint8_t pad;
              uint16_t features;
          } gso;
          struct {
              uint8_t addr[6];
          } mcast;
          struct {
              uint8_t type;
              uint8_t algorithm;
              uint8_t value[4];
          } hash;
          uint16_t pad[3];
      } u;
  };
  typedef struct netif_extra_info netif_extra_info_t;
  
  struct netif_tx_response {
      uint16_t id;
      int16_t  status;
  };
  typedef struct netif_tx_response netif_tx_response_t;
  
  struct netif_rx_request {
      uint16_t    id;        /* Echoed in response message.        */
      uint16_t    pad;
      grant_ref_t gref;
  };
  typedef struct netif_rx_request netif_rx_request_t;
  
  /* Packet data has been validated against protocol checksum. */
  #define _NETRXF_data_validated (0)
  #define  NETRXF_data_validated (1U<<_NETRXF_data_validated)
  
  /* Protocol checksum field is blank in the packet (hardware offload)? */
  #define _NETRXF_csum_blank     (1)
  #define  NETRXF_csum_blank     (1U<<_NETRXF_csum_blank)
  
  /* Packet continues in the next request descriptor. */
  #define _NETRXF_more_data      (2)
  #define  NETRXF_more_data      (1U<<_NETRXF_more_data)
  
  /* Packet to be followed by extra descriptor(s). */
  #define _NETRXF_extra_info     (3)
  #define  NETRXF_extra_info     (1U<<_NETRXF_extra_info)
  
  /* Packet has GSO prefix. Deprecated but included for compatibility */
  #define _NETRXF_gso_prefix     (4)
  #define  NETRXF_gso_prefix     (1U<<_NETRXF_gso_prefix)
  
  struct netif_rx_response {
      uint16_t id;
      uint16_t offset;
      uint16_t flags;
      int16_t  status;
  };
  typedef struct netif_rx_response netif_rx_response_t;
  
  /*
   * Generate netif ring structures and types.
   */
  
  DEFINE_RING_TYPES(netif_tx, struct netif_tx_request, struct netif_tx_response);
  DEFINE_RING_TYPES(netif_rx, struct netif_rx_request, struct netif_rx_response);
  
  #define NETIF_RSP_DROPPED         -2
  #define NETIF_RSP_ERROR           -1
  #define NETIF_RSP_OKAY             0
  /* No response: used for auxiliary requests (e.g., netif_extra_info_t). */
  #define NETIF_RSP_NULL             1
  
  #endif
  