FreeBSD/Linux Kernel Cross Reference
sys/xen/interface/io/sndif.h

     /******************************************************************************
      * sndif.h
      *
      * Unified sound-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) 2013-2015 GlobalLogic Inc.
     * Copyright (C) 2016-2017 EPAM Systems Inc.
     *
     * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
     *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
     *          Oleksandr Dmytryshyn <oleksandr.dmytryshyn@globallogic.com>
     *          Iurii Konovalenko <iurii.konovalenko@globallogic.com>
     */
    
    #ifndef __XEN_PUBLIC_IO_SNDIF_H__
    #define __XEN_PUBLIC_IO_SNDIF_H__
    
    #include "ring.h"
    #include "../grant_table.h"
    
    /*
     ******************************************************************************
     *                           Protocol version
     ******************************************************************************
     */
    #define XENSND_PROTOCOL_VERSION         2
    
    /*
     ******************************************************************************
     *                  Feature and Parameter Negotiation
     ******************************************************************************
     *
     * Front->back notifications: when enqueuing a new request, sending a
     * notification can be made conditional on xensnd_req (i.e., the generic
     * hold-off mechanism provided by the ring macros). Backends must set
     * xensnd_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
     *
     * Back->front notifications: when enqueuing a new response, sending a
     * notification can be made conditional on xensnd_resp (i.e., the generic
     * hold-off mechanism provided by the ring macros). Frontends must set
     * xensnd_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
     *
     * The two halves of a para-virtual sound card driver utilize nodes within
     * XenStore to communicate capabilities and to negotiate operating parameters.
     * This section enumerates these nodes which reside in the respective front and
     * backend portions of XenStore, following the XenBus convention.
     *
     * All data in XenStore is stored as strings. Nodes specifying numeric
     * values are encoded in decimal. Integer value ranges listed below are
     * expressed as fixed sized integer types capable of storing the conversion
     * of a properly formated node string, without loss of information.
     *
     ******************************************************************************
     *                        Example configuration
     ******************************************************************************
     *
     * Note: depending on the use-case backend can expose more sound cards and
     * PCM devices/streams than the underlying HW physically has by employing
     * SW mixers, configuring virtual sound streams, channels etc.
     *
     * This is an example of backend and frontend configuration:
     *
     *--------------------------------- Backend -----------------------------------
     *
     * /local/domain/0/backend/vsnd/1/0/frontend-id = "1"
     * /local/domain/0/backend/vsnd/1/0/frontend = "/local/domain/1/device/vsnd/0"
     * /local/domain/0/backend/vsnd/1/0/state = "4"
     * /local/domain/0/backend/vsnd/1/0/versions = "1,2"
     *
     *--------------------------------- Frontend ----------------------------------
     *
     * /local/domain/1/device/vsnd/0/backend-id = ""
     * /local/domain/1/device/vsnd/0/backend = "/local/domain/0/backend/vsnd/1/0"
     * /local/domain/1/device/vsnd/0/state = "4"
     * /local/domain/1/device/vsnd/0/version = "1"
     *
     *----------------------------- Card configuration ----------------------------
     *
     * /local/domain/1/device/vsnd/0/short-name = "Card short name"
     * /local/domain/1/device/vsnd/0/long-name = "Card long name"
     * /local/domain/1/device/vsnd/0/sample-rates = "8000,32000,44100,48000,96000"
    * /local/domain/1/device/vsnd/0/sample-formats = "s8,u8,s16_le,s16_be"
    * /local/domain/1/device/vsnd/0/buffer-size = "262144"
    *
    *------------------------------- PCM device 0 --------------------------------
    *
    * /local/domain/1/device/vsnd/0/0/name = "General analog"
    * /local/domain/1/device/vsnd/0/0/channels-max = "5"
    *
    *----------------------------- Stream 0, playback ----------------------------
    *
    * /local/domain/1/device/vsnd/0/0/0/type = "p"
    * /local/domain/1/device/vsnd/0/0/0/sample-formats = "s8,u8"
    * /local/domain/1/device/vsnd/0/0/0/unique-id = ""
    *
    * /local/domain/1/device/vsnd/0/0/0/ring-ref = "386"
    * /local/domain/1/device/vsnd/0/0/0/event-channel = "15"
    * /local/domain/1/device/vsnd/0/0/0/evt-ring-ref = "1386"
    * /local/domain/1/device/vsnd/0/0/0/evt-event-channel = "215"
    *
    *------------------------------ Stream 1, capture ----------------------------
    *
    * /local/domain/1/device/vsnd/0/0/1/type = "c"
    * /local/domain/1/device/vsnd/0/0/1/channels-max = "2"
    * /local/domain/1/device/vsnd/0/0/1/unique-id = "1"
    *
    * /local/domain/1/device/vsnd/0/0/1/ring-ref = "384"
    * /local/domain/1/device/vsnd/0/0/1/event-channel = "13"
    * /local/domain/1/device/vsnd/0/0/1/evt-ring-ref = "1384"
    * /local/domain/1/device/vsnd/0/0/1/evt-event-channel = "213"
    *
    *------------------------------- PCM device 1 --------------------------------
    *
    * /local/domain/1/device/vsnd/0/1/name = "HDMI-0"
    * /local/domain/1/device/vsnd/0/1/sample-rates = "8000,32000,44100"
    *
    *------------------------------ Stream 0, capture ----------------------------
    *
    * /local/domain/1/device/vsnd/0/1/0/type = "c"
    * /local/domain/1/device/vsnd/0/1/0/unique-id = "2"
    *
    * /local/domain/1/device/vsnd/0/1/0/ring-ref = "387"
    * /local/domain/1/device/vsnd/0/1/0/event-channel = "151"
    * /local/domain/1/device/vsnd/0/1/0/evt-ring-ref = "1387"
    * /local/domain/1/device/vsnd/0/1/0/evt-event-channel = "351"
    *
    *------------------------------- PCM device 2 --------------------------------
    *
    * /local/domain/1/device/vsnd/0/2/name = "SPDIF"
    *
    *----------------------------- Stream 0, playback ----------------------------
    *
    * /local/domain/1/device/vsnd/0/2/0/type = "p"
    * /local/domain/1/device/vsnd/0/2/0/unique-id = "3"
    *
    * /local/domain/1/device/vsnd/0/2/0/ring-ref = "389"
    * /local/domain/1/device/vsnd/0/2/0/event-channel = "152"
    * /local/domain/1/device/vsnd/0/2/0/evt-ring-ref = "1389"
    * /local/domain/1/device/vsnd/0/2/0/evt-event-channel = "452"
    *
    ******************************************************************************
    *                            Backend XenBus Nodes
    ******************************************************************************
    *
    *----------------------------- Protocol version ------------------------------
    *
    * versions
    *      Values:         <string>
    *
    *      List of XENSND_LIST_SEPARATOR separated protocol versions supported
    *      by the backend. For example "1,2,3".
    *
    ******************************************************************************
    *                            Frontend XenBus Nodes
    ******************************************************************************
    *
    *-------------------------------- Addressing ---------------------------------
    *
    * dom-id
    *      Values:         <uint16_t>
    *
    *      Domain identifier.
    *
    * dev-id
    *      Values:         <uint16_t>
    *
    *      Device identifier.
    *
    * pcm-dev-idx
    *      Values:         <uint8_t>
    *
    *      Zero based contigous index of the PCM device.
    *
    * stream-idx
    *      Values:         <uint8_t>
    *
    *      Zero based contigous index of the stream of the PCM device.
    *
    * The following pattern is used for addressing:
    *   /local/domain/<dom-id>/device/vsnd/<dev-id>/<pcm-dev-idx>/<stream-idx>/...
    *
    *----------------------------- Protocol version ------------------------------
    *
    * version
    *      Values:         <string>
    *
    *      Protocol version, chosen among the ones supported by the backend.
    *
    *------------------------------- PCM settings --------------------------------
    *
    * Every virtualized sound frontend has a set of PCM devices and streams, each
    * could be individually configured. Part of the PCM configuration can be
    * defined at higher level of the hierarchy and be fully or partially re-used
    * by the underlying layers. These configuration values are:
    *  o number of channels (min/max)
    *  o supported sample rates
    *  o supported sample formats.
    * E.g. one can define these values for the whole card, device or stream.
    * Every underlying layer in turn can re-define some or all of them to better
    * fit its needs. For example, card may define number of channels to be
    * in [1; 8] range, and some particular stream may be limited to [1; 2] only.
    * The rule is that the underlying layer must be a subset of the upper layer
    * range.
    *
    * channels-min
    *      Values:         <uint8_t>
    *
    *      The minimum amount of channels that is supported, [1; channels-max].
    *      Optional, if not set or omitted a value of 1 is used.
    *
    * channels-max
    *      Values:         <uint8_t>
    *
    *      The maximum amount of channels that is supported.
    *      Must be at least <channels-min>.
    *
    * sample-rates
    *      Values:         <list of uint32_t>
    *
    *      List of supported sample rates separated by XENSND_LIST_SEPARATOR.
    *      Sample rates are expressed as a list of decimal values w/o any
    *      ordering requirement.
    *
    * sample-formats
    *      Values:         <list of XENSND_PCM_FORMAT_XXX_STR>
    *
    *      List of supported sample formats separated by XENSND_LIST_SEPARATOR.
    *      Items must not exceed XENSND_SAMPLE_FORMAT_MAX_LEN length.
    *
    * buffer-size
    *      Values:         <uint32_t>
    *
    *      The maximum size in octets of the buffer to allocate per stream.
    *
    *----------------------- Virtual sound card settings -------------------------
    * short-name
    *      Values:         <char[32]>
    *
    *      Short name of the virtual sound card. Optional.
    *
    * long-name
    *      Values:         <char[80]>
    *
    *      Long name of the virtual sound card. Optional.
    *
    *----------------------------- Device settings -------------------------------
    * name
    *      Values:         <char[80]>
    *
    *      Name of the sound device within the virtual sound card. Optional.
    *
    *----------------------------- Stream settings -------------------------------
    *
    * type
    *      Values:         "p", "c"
    *
    *      Stream type: "p" - playback stream, "c" - capture stream
    *
    *      If both capture and playback are needed then two streams need to be
    *      defined under the same device.
    *
    * unique-id
    *      Values:         <string>
    *
    *      After stream initialization it is assigned a unique ID, so every
    *      stream of the frontend can be identified by the backend by this ID.
    *      This can be UUID or such.
    *
    *-------------------- Stream Request Transport Parameters --------------------
    *
    * event-channel
    *      Values:         <uint32_t>
    *
    *      The identifier of the Xen event channel used to signal activity
    *      in the ring buffer.
    *
    * ring-ref
    *      Values:         <uint32_t>
    *
    *      The Xen grant reference granting permission for the backend to map
    *      a sole page in a single page sized ring buffer.
    *
    *--------------------- Stream Event Transport Parameters ---------------------
    *
    * This communication path is used to deliver asynchronous events from backend
    * to frontend, set up per stream.
    *
    * evt-event-channel
    *      Values:         <uint32_t>
    *
    *      The identifier of the Xen event channel used to signal activity
    *      in the ring buffer.
    *
    * evt-ring-ref
    *      Values:         <uint32_t>
    *
    *      The Xen grant reference granting permission for the backend to map
    *      a sole page in a single page sized ring buffer.
    *
    ******************************************************************************
    *                               STATE DIAGRAMS
    ******************************************************************************
    *
    * Tool stack creates front and back state nodes with initial state
    * XenbusStateInitialising.
    * Tool stack creates and sets up frontend sound configuration nodes per domain.
    *
    * Front                                Back
    * =================================    =====================================
    * XenbusStateInitialising              XenbusStateInitialising
    *                                       o Query backend device identification
    *                                         data.
    *                                       o Open and validate backend device.
    *                                                      |
    *                                                      |
    *                                                      V
    *                                      XenbusStateInitWait
    *
    * o Query frontend configuration
    * o Allocate and initialize
    *   event channels per configured
    *   playback/capture stream.
    * o Publish transport parameters
    *   that will be in effect during
    *   this connection.
    *              |
    *              |
    *              V
    * XenbusStateInitialised
    *
    *                                       o Query frontend transport parameters.
    *                                       o Connect to the event channels.
    *                                                      |
    *                                                      |
    *                                                      V
    *                                      XenbusStateConnected
    *
    *  o Create and initialize OS
    *    virtual sound device instances
    *    as per configuration.
    *              |
    *              |
    *              V
    * XenbusStateConnected
    *
    *                                      XenbusStateUnknown
    *                                      XenbusStateClosed
    *                                      XenbusStateClosing
    * o Remove virtual sound device
    * o Remove event channels
    *              |
    *              |
    *              V
    * XenbusStateClosed
    *
    *------------------------------- Recovery flow -------------------------------
    *
    * In case of frontend unrecoverable errors backend handles that as
    * if frontend goes into the XenbusStateClosed state.
    *
    * In case of backend unrecoverable errors frontend tries removing
    * the virtualized device. If this is possible at the moment of error,
    * then frontend goes into the XenbusStateInitialising state and is ready for
    * new connection with backend. If the virtualized device is still in use and
    * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
    * until either the virtualized device removed or backend initiates a new
    * connection. On the virtualized device removal frontend goes into the
    * XenbusStateInitialising state.
    *
    * Note on XenbusStateReconfiguring state of the frontend: if backend has
    * unrecoverable errors then frontend cannot send requests to the backend
    * and thus cannot provide functionality of the virtualized device anymore.
    * After backend is back to normal the virtualized device may still hold some
    * state: configuration in use, allocated buffers, client application state etc.
    * So, in most cases, this will require frontend to implement complex recovery
    * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
    * frontend will make sure no new clients of the virtualized device are
    * accepted, allow existing client(s) to exit gracefully by signaling error
    * state etc.
    * Once all the clients are gone frontend can reinitialize the virtualized
    * device and get into XenbusStateInitialising state again signaling the
    * backend that a new connection can be made.
    *
    * There are multiple conditions possible under which frontend will go from
    * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
    * specific. For example:
    * 1. The underlying OS framework may provide callbacks to signal that the last
    *    client of the virtualized device has gone and the device can be removed
    * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
    *    to periodically check if this is the right time to re-try removal of
    *    the virtualized device.
    * 3. By any other means.
    *
    ******************************************************************************
    *                             PCM FORMATS
    ******************************************************************************
    *
    * XENSND_PCM_FORMAT_<format>[_<endian>]
    *
    * format: <S/U/F><bits> or <name>
    *     S - signed, U - unsigned, F - float
    *     bits - 8, 16, 24, 32
    *     name - MU_LAW, GSM, etc.
    *
    * endian: <LE/BE>, may be absent
    *     LE - Little endian, BE - Big endian
    */
   #define XENSND_PCM_FORMAT_S8            0
   #define XENSND_PCM_FORMAT_U8            1
   #define XENSND_PCM_FORMAT_S16_LE        2
   #define XENSND_PCM_FORMAT_S16_BE        3
   #define XENSND_PCM_FORMAT_U16_LE        4
   #define XENSND_PCM_FORMAT_U16_BE        5
   #define XENSND_PCM_FORMAT_S24_LE        6
   #define XENSND_PCM_FORMAT_S24_BE        7
   #define XENSND_PCM_FORMAT_U24_LE        8
   #define XENSND_PCM_FORMAT_U24_BE        9
   #define XENSND_PCM_FORMAT_S32_LE        10
   #define XENSND_PCM_FORMAT_S32_BE        11
   #define XENSND_PCM_FORMAT_U32_LE        12
   #define XENSND_PCM_FORMAT_U32_BE        13
   #define XENSND_PCM_FORMAT_F32_LE        14 /* 4-byte float, IEEE-754 32-bit, */
   #define XENSND_PCM_FORMAT_F32_BE        15 /* range -1.0 to 1.0              */
   #define XENSND_PCM_FORMAT_F64_LE        16 /* 8-byte float, IEEE-754 64-bit, */
   #define XENSND_PCM_FORMAT_F64_BE        17 /* range -1.0 to 1.0              */
   #define XENSND_PCM_FORMAT_IEC958_SUBFRAME_LE 18
   #define XENSND_PCM_FORMAT_IEC958_SUBFRAME_BE 19
   #define XENSND_PCM_FORMAT_MU_LAW        20
   #define XENSND_PCM_FORMAT_A_LAW         21
   #define XENSND_PCM_FORMAT_IMA_ADPCM     22
   #define XENSND_PCM_FORMAT_MPEG          23
   #define XENSND_PCM_FORMAT_GSM           24
   
   /*
    ******************************************************************************
    *                             REQUEST CODES
    ******************************************************************************
    */
   #define XENSND_OP_OPEN                  0
   #define XENSND_OP_CLOSE                 1
   #define XENSND_OP_READ                  2
   #define XENSND_OP_WRITE                 3
   #define XENSND_OP_SET_VOLUME            4
   #define XENSND_OP_GET_VOLUME            5
   #define XENSND_OP_MUTE                  6
   #define XENSND_OP_UNMUTE                7
   #define XENSND_OP_TRIGGER               8
   #define XENSND_OP_HW_PARAM_QUERY        9
   
   #define XENSND_OP_TRIGGER_START         0
   #define XENSND_OP_TRIGGER_PAUSE         1
   #define XENSND_OP_TRIGGER_STOP          2
   #define XENSND_OP_TRIGGER_RESUME        3
   
   /*
    ******************************************************************************
    *                                 EVENT CODES
    ******************************************************************************
    */
   #define XENSND_EVT_CUR_POS              0
   
   /*
    ******************************************************************************
    *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
    ******************************************************************************
    */
   #define XENSND_DRIVER_NAME              "vsnd"
   
   #define XENSND_LIST_SEPARATOR           ","
   /* Field names */
   #define XENSND_FIELD_BE_VERSIONS        "versions"
   #define XENSND_FIELD_FE_VERSION         "version"
   #define XENSND_FIELD_VCARD_SHORT_NAME   "short-name"
   #define XENSND_FIELD_VCARD_LONG_NAME    "long-name"
   #define XENSND_FIELD_RING_REF           "ring-ref"
   #define XENSND_FIELD_EVT_CHNL           "event-channel"
   #define XENSND_FIELD_EVT_RING_REF       "evt-ring-ref"
   #define XENSND_FIELD_EVT_EVT_CHNL       "evt-event-channel"
   #define XENSND_FIELD_DEVICE_NAME        "name"
   #define XENSND_FIELD_TYPE               "type"
   #define XENSND_FIELD_STREAM_UNIQUE_ID   "unique-id"
   #define XENSND_FIELD_CHANNELS_MIN       "channels-min"
   #define XENSND_FIELD_CHANNELS_MAX       "channels-max"
   #define XENSND_FIELD_SAMPLE_RATES       "sample-rates"
   #define XENSND_FIELD_SAMPLE_FORMATS     "sample-formats"
   #define XENSND_FIELD_BUFFER_SIZE        "buffer-size"
   
   /* Stream type field values. */
   #define XENSND_STREAM_TYPE_PLAYBACK     "p"
   #define XENSND_STREAM_TYPE_CAPTURE      "c"
   /* Sample rate max string length */
   #define XENSND_SAMPLE_RATE_MAX_LEN      11
   /* Sample format field values */
   #define XENSND_SAMPLE_FORMAT_MAX_LEN    24
   
   #define XENSND_PCM_FORMAT_S8_STR        "s8"
   #define XENSND_PCM_FORMAT_U8_STR        "u8"
   #define XENSND_PCM_FORMAT_S16_LE_STR    "s16_le"
   #define XENSND_PCM_FORMAT_S16_BE_STR    "s16_be"
   #define XENSND_PCM_FORMAT_U16_LE_STR    "u16_le"
   #define XENSND_PCM_FORMAT_U16_BE_STR    "u16_be"
   #define XENSND_PCM_FORMAT_S24_LE_STR    "s24_le"
   #define XENSND_PCM_FORMAT_S24_BE_STR    "s24_be"
   #define XENSND_PCM_FORMAT_U24_LE_STR    "u24_le"
   #define XENSND_PCM_FORMAT_U24_BE_STR    "u24_be"
   #define XENSND_PCM_FORMAT_S32_LE_STR    "s32_le"
   #define XENSND_PCM_FORMAT_S32_BE_STR    "s32_be"
   #define XENSND_PCM_FORMAT_U32_LE_STR    "u32_le"
   #define XENSND_PCM_FORMAT_U32_BE_STR    "u32_be"
   #define XENSND_PCM_FORMAT_F32_LE_STR    "float_le"
   #define XENSND_PCM_FORMAT_F32_BE_STR    "float_be"
   #define XENSND_PCM_FORMAT_F64_LE_STR    "float64_le"
   #define XENSND_PCM_FORMAT_F64_BE_STR    "float64_be"
   #define XENSND_PCM_FORMAT_IEC958_SUBFRAME_LE_STR "iec958_subframe_le"
   #define XENSND_PCM_FORMAT_IEC958_SUBFRAME_BE_STR "iec958_subframe_be"
   #define XENSND_PCM_FORMAT_MU_LAW_STR    "mu_law"
   #define XENSND_PCM_FORMAT_A_LAW_STR     "a_law"
   #define XENSND_PCM_FORMAT_IMA_ADPCM_STR "ima_adpcm"
   #define XENSND_PCM_FORMAT_MPEG_STR      "mpeg"
   #define XENSND_PCM_FORMAT_GSM_STR       "gsm"
   
   
   /*
    ******************************************************************************
    *                          STATUS RETURN CODES
    ******************************************************************************
    *
    * Status return code is zero on success and -XEN_EXX on failure.
    *
    ******************************************************************************
    *                              Assumptions
    ******************************************************************************
    * o usage of grant reference 0 as invalid grant reference:
    *   grant reference 0 is valid, but never exposed to a PV driver,
    *   because of the fact it is already in use/reserved by the PV console.
    * o all references in this document to page sizes must be treated
    *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
    *
    ******************************************************************************
    *       Description of the protocol between frontend and backend driver
    ******************************************************************************
    *
    * The two halves of a Para-virtual sound driver communicate with
    * each other using shared pages and event channels.
    * Shared page contains a ring with request/response packets.
    *
    * Packets, used for input/output operations, e.g. read/write, set/get volume,
    * etc., provide offset/length fields in order to allow asynchronous protocol
    * operation with buffer space sharing: part of the buffer allocated at
    * XENSND_OP_OPEN can be used for audio samples and part, for example,
    * for volume control.
    *
    * All reserved fields in the structures below must be 0.
    *
    *---------------------------------- Requests ---------------------------------
    *
    * All request packets have the same length (64 octets)
    * All request packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |    operation   |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    *   id - uint16_t, private guest value, echoed in response
    *   operation - uint8_t, operation code, XENSND_OP_???
    *
    * For all packets which use offset and length:
    *   offset - uint32_t, read or write data offset within the shared buffer,
    *     passed with XENSND_OP_OPEN request, octets,
    *     [0; XENSND_OP_OPEN.buffer_sz - 1].
    *   length - uint32_t, read or write data length, octets
    *
    * Request open - open a PCM stream for playback or capture:
    *
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | XENSND_OP_OPEN |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                             pcm_rate                              | 12
    * +----------------+----------------+----------------+----------------+
    * |  pcm_format    |  pcm_channels  |             reserved            | 16
    * +----------------+----------------+----------------+----------------+
    * |                             buffer_sz                             | 20
    * +----------------+----------------+----------------+----------------+
    * |                           gref_directory                          | 24
    * +----------------+----------------+----------------+----------------+
    * |                             period_sz                             | 28
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 32
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * pcm_rate - uint32_t, stream data rate, Hz
    * pcm_format - uint8_t, XENSND_PCM_FORMAT_XXX value
    * pcm_channels - uint8_t, number of channels of this stream,
    *   [channels-min; channels-max]
    * buffer_sz - uint32_t, buffer size to be allocated, octets
    * period_sz - uint32_t, event period size, octets
    *   This is the requested value of the period at which frontend would
    *   like to receive XENSND_EVT_CUR_POS notifications from the backend when
    *   stream position advances during playback/capture.
    *   It shows how many octets are expected to be played/captured before
    *   sending such an event.
    *   If set to 0 no XENSND_EVT_CUR_POS events are sent by the backend.
    *
    * gref_directory - grant_ref_t, a reference to the first shared page
    *   describing shared buffer references. At least one page exists. If shared
    *   buffer size  (buffer_sz) exceeds what can be addressed by this single page,
    *   then reference to the next page must be supplied (see gref_dir_next_page
    *   below)
    */
   
   struct xensnd_open_req {
       uint32_t pcm_rate;
       uint8_t pcm_format;
       uint8_t pcm_channels;
       uint16_t reserved;
       uint32_t buffer_sz;
       grant_ref_t gref_directory;
       uint32_t period_sz;
   };
   
   /*
    * Shared page for XENSND_OP_OPEN buffer descriptor (gref_directory in the
    *   request) employs a list of pages, describing all pages of the shared data
    *   buffer:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |                        gref_dir_next_page                         | 4
    * +----------------+----------------+----------------+----------------+
    * |                              gref[0]                              | 8
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                              gref[i]                              | i*4+8
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             gref[N - 1]                           | N*4+8
    * +----------------+----------------+----------------+----------------+
    *
    * gref_dir_next_page - grant_ref_t, reference to the next page describing
    *   page directory. Must be 0 if there are no more pages in the list.
    * gref[i] - grant_ref_t, reference to a shared page of the buffer
    *   allocated at XENSND_OP_OPEN
    *
    * Number of grant_ref_t entries in the whole page directory is not
    * passed, but instead can be calculated as:
    *   num_grefs_total = (XENSND_OP_OPEN.buffer_sz + XEN_PAGE_SIZE - 1) /
    *       XEN_PAGE_SIZE
    */
   
   struct xensnd_page_directory {
       grant_ref_t gref_dir_next_page;
       grant_ref_t gref[1]; /* Variable length */
   };
   
   /*
    *  Request close - close an opened pcm stream:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | XENSND_OP_CLOSE|    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Request read/write - used for read (for capture) or write (for playback):
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   operation    |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                              offset                               | 12
    * +----------------+----------------+----------------+----------------+
    * |                              length                               | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * operation - XENSND_OP_READ for read or XENSND_OP_WRITE for write
    */
   
   struct xensnd_rw_req {
       uint32_t offset;
       uint32_t length;
   };
   
   /*
    * Request set/get volume - set/get channels' volume of the stream given:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   operation    |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                              offset                               | 12
    * +----------------+----------------+----------------+----------------+
    * |                              length                               | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * operation - XENSND_OP_SET_VOLUME for volume set
    *   or XENSND_OP_GET_VOLUME for volume get
    * Buffer passed with XENSND_OP_OPEN is used to exchange volume
    * values:
    *
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |                             channel[0]                            | 4
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             channel[i]                            | i*4
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                           channel[N - 1]                          | (N-1)*4
    * +----------------+----------------+----------------+----------------+
    *
    * N = XENSND_OP_OPEN.pcm_channels
    * i - uint8_t, index of a channel
    * channel[i] - sint32_t, volume of i-th channel
    * Volume is expressed as a signed value in steps of 0.001 dB,
    * while 0 being 0 dB.
    *
    * Request mute/unmute - mute/unmute stream:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   operation    |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                              offset                               | 12
    * +----------------+----------------+----------------+----------------+
    * |                              length                               | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * operation - XENSND_OP_MUTE for mute or XENSND_OP_UNMUTE for unmute
    * Buffer passed with XENSND_OP_OPEN is used to exchange mute/unmute
    * values:
    *
    *                                   0                                 octet
    * +----------------+----------------+----------------+----------------+
    * |                             channel[0]                            | 4
    * +----------------+----------------+----------------+----------------+
    * +/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             channel[i]                            | i*4
    * +----------------+----------------+----------------+----------------+
    * +/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                           channel[N - 1]                          | (N-1)*4
    * +----------------+----------------+----------------+----------------+
    *
    * N = XENSND_OP_OPEN.pcm_channels
    * i - uint8_t, index of a channel
    * channel[i] - uint8_t, non-zero if i-th channel needs to be muted/unmuted
    *
    *------------------------------------ N.B. -----------------------------------
    *
    * The 'struct xensnd_rw_req' is also used for XENSND_OP_SET_VOLUME,
    * XENSND_OP_GET_VOLUME, XENSND_OP_MUTE, XENSND_OP_UNMUTE.
    *
    * Request stream running state change - trigger PCM stream running state
    * to start, stop, pause or resume:
    *
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   _OP_TRIGGER  |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |      type      |                     reserved                     | 12
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 16
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * type - uint8_t, XENSND_OP_TRIGGER_XXX value
    */
   
   struct xensnd_trigger_req {
       uint8_t type;
   };
   
   /*
    * Request stream parameter ranges: request intervals and
    *   masks of supported ranges for stream configuration values.
    *
    *   Sound device configuration for a particular stream is a limited subset
    *   of the multidimensional configuration available on XenStore, e.g.
    *   once the frame rate has been selected there is a limited supported range
    *   for sample rates becomes available (which might be the same set configured
    *   on XenStore or less). For example, selecting 96kHz sample rate may limit
    *   number of channels available for such configuration from 4 to 2, etc.
    *   Thus, each call to XENSND_OP_HW_PARAM_QUERY may reduce configuration
    *   space making it possible to iteratively get the final stream configuration,
    *   used in XENSND_OP_OPEN request.
    *
    *   See response format for this request.
    *
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | _HW_PARAM_QUERY|    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                     formats mask low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                     formats mask high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                              min rate                             | 20
    * +----------------+----------------+----------------+----------------+
    * |                              max rate                             | 24
    * +----------------+----------------+----------------+----------------+
    * |                            min channels                           | 28
    * +----------------+----------------+----------------+----------------+
    * |                            max channels                           | 32
    * +----------------+----------------+----------------+----------------+
    * |                         min buffer frames                         | 36
    * +----------------+----------------+----------------+----------------+
    * |                         max buffer frames                         | 40
    * +----------------+----------------+----------------+----------------+
    * |                         min period frames                         | 44
    * +----------------+----------------+----------------+----------------+
    * |                         max period frames                         | 48
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 52
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * formats - uint64_t, bit mask representing values of the parameter
    *   made as bitwise OR of (1 << XENSND_PCM_FORMAT_XXX) values
    *
    * For interval parameters:
    *   min - uint32_t, minimum value of the parameter
    *   max - uint32_t, maximum value of the parameter
    *
    * Frame is defined as a product of the number of channels by the
    * number of octets per one sample.
    */
   
   struct xensnd_query_hw_param {
       uint64_t formats;
       struct {
           uint32_t min;
           uint32_t max;
       } rates;
       struct {
           uint32_t min;
           uint32_t max;
       } channels;
       struct {
           uint32_t min;
           uint32_t max;
       } buffer;
       struct {
           uint32_t min;
           uint32_t max;
       } period;
   };
   
   /*
    *---------------------------------- Responses --------------------------------
    *
    * All response packets have the same length (64 octets)
    *
    * All response packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |    operation   |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                              status                               | 8
    * +----------------+----------------+----------------+----------------+
    *
    * id - uint16_t, copied from the request
    * operation - uint8_t, XENSND_OP_* - copied from request
    * status - int32_t, response status, zero on success and -XEN_EXX on failure
    *
    *
    * HW parameter query response - response for XENSND_OP_HW_PARAM_QUERY:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |    operation   |    reserved    | 4
    * +----------------+----------------+----------------+----------------+
    * |                              status                               | 8
    * +----------------+----------------+----------------+----------------+
    * |                     formats mask low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                     formats mask high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                              min rate                             | 20
    * +----------------+----------------+----------------+----------------+
    * |                              max rate                             | 24
    * +----------------+----------------+----------------+----------------+
    * |                            min channels                           | 28
    * +----------------+----------------+----------------+----------------+
    * |                            max channels                           | 32
    * +----------------+----------------+----------------+----------------+
    * |                         min buffer frames                         | 36
    * +----------------+----------------+----------------+----------------+
    * |                         max buffer frames                         | 40
    * +----------------+----------------+----------------+----------------+
    * |                         min period frames                         | 44
    * +----------------+----------------+----------------+----------------+
    * |                         max period frames                         | 48
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 52
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Meaning of the values in this response is the same as for
    * XENSND_OP_HW_PARAM_QUERY request.
    */
   
   /*
    *----------------------------------- Events ----------------------------------
    *
    * Events are sent via shared page allocated by the front and propagated by
    *   evt-event-channel/evt-ring-ref XenStore entries
    * All event packets have the same length (64 octets)
    * All event packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |      type      |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    *
    * id - uint16_t, event id, may be used by front
    * type - uint8_t, type of the event
    *
    *
    * Current stream position - event from back to front when stream's
    *   playback/capture position has advanced:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   _EVT_CUR_POS |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                         position low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                         position high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
   * +----------------+----------------+----------------+----------------+
   * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
   * +----------------+----------------+----------------+----------------+
   * |                             reserved                              | 64
   * +----------------+----------------+----------------+----------------+
   *
   * position - current value of stream's playback/capture position, octets
   *
   */
  
  struct xensnd_cur_pos_evt {
      uint64_t position;
  };
  
  struct xensnd_req {
      uint16_t id;
      uint8_t operation;
      uint8_t reserved[5];
      union {
          struct xensnd_open_req open;
          struct xensnd_rw_req rw;
          struct xensnd_trigger_req trigger;
          struct xensnd_query_hw_param hw_param;
          uint8_t reserved[56];
      } op;
  };
  
  struct xensnd_resp {
      uint16_t id;
      uint8_t operation;
      uint8_t reserved;
      int32_t status;
      union {
          struct xensnd_query_hw_param hw_param;
          uint8_t reserved1[56];
      } resp;
  };
  
  struct xensnd_evt {
      uint16_t id;
      uint8_t type;
      uint8_t reserved[5];
      union {
          struct xensnd_cur_pos_evt cur_pos;
          uint8_t reserved[56];
      } op;
  };
  
  DEFINE_RING_TYPES(xen_sndif, struct xensnd_req, struct xensnd_resp);
  
  /*
   ******************************************************************************
   *                        Back to front events delivery
   ******************************************************************************
   * In order to deliver asynchronous events from back to front a shared page is
   * allocated by front and its granted reference propagated to back via
   * XenStore entries (evt-ring-ref/evt-event-channel).
   * This page has a common header used by both front and back to synchronize
   * access and control event's ring buffer, while back being a producer of the
   * events and front being a consumer. The rest of the page after the header
   * is used for event packets.
   *
   * Upon reception of an event(s) front may confirm its reception
   * for either each event, group of events or none.
   */
  
  struct xensnd_event_page {
      uint32_t in_cons;
      uint32_t in_prod;
      uint8_t reserved[56];
  };
  
  #define XENSND_EVENT_PAGE_SIZE 4096
  #define XENSND_IN_RING_OFFS (sizeof(struct xensnd_event_page))
  #define XENSND_IN_RING_SIZE (XENSND_EVENT_PAGE_SIZE - XENSND_IN_RING_OFFS)
  #define XENSND_IN_RING_LEN (XENSND_IN_RING_SIZE / sizeof(struct xensnd_evt))
  #define XENSND_IN_RING(page) \
      ((struct xensnd_evt *)((char *)(page) + XENSND_IN_RING_OFFS))
  #define XENSND_IN_RING_REF(page, idx) \
      (XENSND_IN_RING((page))[(idx) % XENSND_IN_RING_LEN])
  
  #endif /* __XEN_PUBLIC_IO_SNDIF_H__ */
  
  /*
   * Local variables:
   * mode: C
   * c-file-style: "BSD"
   * c-basic-offset: 4
   * tab-width: 4
   * indent-tabs-mode: nil
   * End:
   */

Cache object: 4a76df77aa0de37d4d5faa28f42d0aa8