    /* SPDX-License-Identifier: MIT */
    /******************************************************************************
     * netif.h
     *
     * Unified network-device I/O interface for Xen guest OSes.
     *
     * 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.
     */

    /*
     * The setting of "trusted" node to "0" in the frontend path signals that the
     * frontend should not trust the backend, and should deploy whatever measures
     * available to protect from a malicious backend on the other end.
     */

    /*
     * 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/vif/<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.
     */

    /*
     * Link state
     * ==========
     *
     * The backend can advertise its current link (carrier) state to the
     * frontend using the /local/domain/X/backend/vif/<domid>/<vif>/carrier
     * node. If this node is not present, then the frontend should assume that
     * the link is up (for compatibility with backends that do not implement
     * this feature). If this node is present, then a value of "0" should be
     * interpreted by the frontend as the link being down (no carrier) and a
     * value of "1" should be interpreted as the link being up (carrier
     * present).
     */

    /*
     * MTU
     * ===
     *
     * The toolstack may set a value of MTU for the frontend by setting the
     * /local/domain/<domid>/device/vif/<vif>/mtu node with the MTU value in
     * octets. If this node is absent the frontend should assume an MTU value
     * of 1500 octets. A frontend is also at liberty to ignore this value so
     * it is only suitable for informing the frontend that a packet payload
     * >1500 octets is permitted.
     */

    /*
     * 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

    /*
     * This algorithm uses a 'key' as well as the data buffer itself.
     * (Buffer[] and Key[] are treated as shift-registers where the MSB of
     * Buffer/Key[0] is considered 'left-most' and the LSB of Buffer/Key[N-1]
     * is the 'right-most').
     *
     * Value = 0
     * For number of bits in Buffer[]
     *    If (left-most bit of Buffer[] is 1)
     *        Value ^= left-most 32 bits of Key[]
     *    Key[] << 1
     *    Buffer[] << 1
     *
     * The code below is provided for convenience where an operating system
     * does not already provide an implementation.
     */
    #ifdef XEN_NETIF_DEFINE_TOEPLITZ
    static uint32_t xen_netif_toeplitz_hash(const uint8_t *key,
                                            unsigned int keylen,
                                            const uint8_t *buf,
                                            unsigned int buflen)
    {
        unsigned int keyi, bufi;
        uint64_t prefix = 0;
        uint64_t hash = 0;

        /* Pre-load prefix with the first 8 bytes of the key */
        for (keyi = 0; keyi < 8; keyi++) {
            prefix <<= 8;
            prefix |= (keyi < keylen) ? key[keyi] : 0;
        }

        for (bufi = 0; bufi < buflen; bufi++) {
            uint8_t byte = buf[bufi];
            unsigned int bit;

            for (bit = 0; bit < 8; bit++) {
                if (byte & 0x80)
                    hash ^= prefix;
                prefix <<= 1;
                byte <<=1;
            }

            /*
             * 'prefix' has now been left-shifted by 8, so
             * OR in the next byte.
             */
            prefix |= (keyi < keylen) ? key[keyi] : 0;
            keyi++;
        }

        /* The valid part of the hash is in the upper 32 bits. */
        return hash >> 32;
    }
    #endif /* XEN_NETIF_DEFINE_TOEPLITZ */

    /*
     * 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

    /*
     * Local variables:
     * mode: C
     * c-file-style: "BSD"
     * c-basic-offset: 4
     * tab-width: 4
     * indent-tabs-mode: nil
     * End:
     */