docs/interop/vhost-user-gpu.rst

   1 =======================
   2 Vhost-user-gpu Protocol
   3 =======================
   4
   5 :Licence: This work is licensed under the terms of the GNU GPL,
   6           version 2 or later. See the COPYING file in the top-level
   7           directory.
   8
   9 .. contents:: Table of Contents
  10
  11 Introduction
  12 ============
  13
  14 The vhost-user-gpu protocol is aiming at sharing the rendering result
  15 of a virtio-gpu, done from a vhost-user slave process to a vhost-user
  16 master process (such as QEMU). It bears a resemblance to a display
  17 server protocol, if you consider QEMU as the display server and the
  18 slave as the client, but in a very limited way. Typically, it will
  19 work by setting a scanout/display configuration, before sending flush
  20 events for the display updates. It will also update the cursor shape
  21 and position.
  22
  23 The protocol is sent over a UNIX domain stream socket, since it uses
  24 socket ancillary data to share opened file descriptors (DMABUF fds or
  25 shared memory). The socket is usually obtained via
  26 ``VHOST_USER_GPU_SET_SOCKET``.
  27
  28 Requests are sent by the *slave*, and the optional replies by the
  29 *master*.
  30
  31 Wire format
  32 ===========
  33
  34 Unless specified differently, numbers are in the machine native byte
  35 order.
  36
  37 A vhost-user-gpu message (request and reply) consists of 3 header
  38 fields and a payload.
  39
  40 +---------+-------+------+---------+
  41 | request | flags | size | payload |
  42 +---------+-------+------+---------+
  43
  44 Header
  45 ------
  46
  47 :request: ``u32``, type of the request
  48
  49 :flags: ``u32``, 32-bit bit field:
  50
  51  - Bit 2 is the reply flag - needs to be set on each reply
  52
  53 :size: ``u32``, size of the payload
  54
  55 Payload types
  56 -------------
  57
  58 Depending on the request type, **payload** can be:
  59
  60 VhostUserGpuCursorPos
  61 ^^^^^^^^^^^^^^^^^^^^^
  62
  63 +------------+---+---+
  64 | scanout-id | x | y |
  65 +------------+---+---+
  66
  67 :scanout-id: ``u32``, the scanout where the cursor is located
  68
  69 :x/y: ``u32``, the cursor position
  70
  71 VhostUserGpuCursorUpdate
  72 ^^^^^^^^^^^^^^^^^^^^^^^^
  73
  74 +-----+-------+-------+--------+
  75 | pos | hot_x | hot_y | cursor |
  76 +-----+-------+-------+--------+
  77
  78 :pos: a ``VhostUserGpuCursorPos``, the cursor location
  79
  80 :hot_x/hot_y: ``u32``, the cursor hot location
  81
  82 :cursor: ``[u32; 64 * 64]``, 64x64 RGBA cursor data (PIXMAN_a8r8g8b8 format)
  83
  84 VhostUserGpuScanout
  85 ^^^^^^^^^^^^^^^^^^^
  86
  87 +------------+---+---+
  88 | scanout-id | w | h |
  89 +------------+---+---+
  90
  91 :scanout-id: ``u32``, the scanout configuration to set
  92
  93 :w/h: ``u32``, the scanout width/height size
  94
  95 VhostUserGpuUpdate
  96 ^^^^^^^^^^^^^^^^^^
  97
  98 +------------+---+---+---+---+------+
  99 | scanout-id | x | y | w | h | data |
 100 +------------+---+---+---+---+------+
 101
 102 :scanout-id: ``u32``, the scanout content to update
 103
 104 :x/y/w/h: ``u32``, region of the update
 105
 106 :data: RGB data (PIXMAN_x8r8g8b8 format)
 107
 108 VhostUserGpuDMABUFScanout
 109 ^^^^^^^^^^^^^^^^^^^^^^^^^
 110
 111 +------------+---+---+---+---+-----+-----+--------+-------+--------+
 112 | scanout-id | x | y | w | h | fdw | fwh | stride | flags | fourcc |
 113 +------------+---+---+---+---+-----+-----+--------+-------+--------+
 114
 115 :scanout-id: ``u32``, the scanout configuration to set
 116
 117 :x/y: ``u32``, the location of the scanout within the DMABUF
 118
 119 :w/h: ``u32``, the scanout width/height size
 120
 121 :fdw/fdh/stride/flags: ``u32``, the DMABUF width/height/stride/flags
 122
 123 :fourcc: ``i32``, the DMABUF fourcc
 124
 125
 126 C structure
 127 -----------
 128
 129 In QEMU the vhost-user-gpu message is implemented with the following struct:
 130
 131 .. code:: c
 132
 133   typedef struct VhostUserGpuMsg {
 134       uint32_t request; /* VhostUserGpuRequest */
 135       uint32_t flags;
 136       uint32_t size; /* the following payload size */
 137       union {
 138           VhostUserGpuCursorPos cursor_pos;
 139           VhostUserGpuCursorUpdate cursor_update;
 140           VhostUserGpuScanout scanout;
 141           VhostUserGpuUpdate update;
 142           VhostUserGpuDMABUFScanout dmabuf_scanout;
 143           struct virtio_gpu_resp_display_info display_info;
 144           uint64_t u64;
 145       } payload;
 146   } QEMU_PACKED VhostUserGpuMsg;
 147
 148 Protocol features
 149 -----------------
 150
 151 None yet.
 152
 153 As the protocol may need to evolve, new messages and communication
 154 changes are negotiated thanks to preliminary
 155 ``VHOST_USER_GPU_GET_PROTOCOL_FEATURES`` and
 156 ``VHOST_USER_GPU_SET_PROTOCOL_FEATURES`` requests.
 157
 158 Communication
 159 =============
 160
 161 Message types
 162 -------------
 163
 164 ``VHOST_USER_GPU_GET_PROTOCOL_FEATURES``
 165   :id: 1
 166   :request payload: N/A
 167   :reply payload: ``u64``
 168
 169   Get the supported protocol features bitmask.
 170
 171 ``VHOST_USER_GPU_SET_PROTOCOL_FEATURES``
 172   :id: 2
 173   :request payload: ``u64``
 174   :reply payload: N/A
 175
 176   Enable protocol features using a bitmask.
 177
 178 ``VHOST_USER_GPU_GET_DISPLAY_INFO``
 179   :id: 3
 180   :request payload: N/A
 181   :reply payload: ``struct virtio_gpu_resp_display_info`` (from virtio specification)
 182
 183   Get the preferred display configuration.
 184
 185 ``VHOST_USER_GPU_CURSOR_POS``
 186   :id: 4
 187   :request payload: ``VhostUserGpuCursorPos``
 188   :reply payload: N/A
 189
 190   Set/show the cursor position.
 191
 192 ``VHOST_USER_GPU_CURSOR_POS_HIDE``
 193   :id: 5
 194   :request payload: ``VhostUserGpuCursorPos``
 195   :reply payload: N/A
 196
 197   Set/hide the cursor.
 198
 199 ``VHOST_USER_GPU_CURSOR_UPDATE``
 200   :id: 6
 201   :request payload: ``VhostUserGpuCursorUpdate``
 202   :reply payload: N/A
 203
 204   Update the cursor shape and location.
 205
 206 ``VHOST_USER_GPU_SCANOUT``
 207   :id: 7
 208   :request payload: ``VhostUserGpuScanout``
 209   :reply payload: N/A
 210
 211   Set the scanout resolution. To disable a scanout, the dimensions
 212   width/height are set to 0.
 213
 214 ``VHOST_USER_GPU_UPDATE``
 215   :id: 8
 216   :request payload: ``VhostUserGpuUpdate``
 217   :reply payload: N/A
 218
 219   Update the scanout content. The data payload contains the graphical bits.
 220   The display should be flushed and presented.
 221
 222 ``VHOST_USER_GPU_DMABUF_SCANOUT``
 223   :id: 9
 224   :request payload: ``VhostUserGpuDMABUFScanout``
 225   :reply payload: N/A
 226
 227   Set the scanout resolution/configuration, and share a DMABUF file
 228   descriptor for the scanout content, which is passed as ancillary
 229   data. To disable a scanout, the dimensions width/height are set
 230   to 0, there is no file descriptor passed.
 231
 232 ``VHOST_USER_GPU_DMABUF_UPDATE``
 233   :id: 10
 234   :request payload: ``VhostUserGpuUpdate``
 235   :reply payload: empty payload
 236
 237   The display should be flushed and presented according to updated
 238   region from ``VhostUserGpuUpdate``.
 239
 240   Note: there is no data payload, since the scanout is shared thanks
 241   to DMABUF, that must have been set previously with
 242   ``VHOST_USER_GPU_DMABUF_SCANOUT``.