docs/interop/vhost-user-gpu.rst

   1 =======================
   2 Vhost-user-gpu Protocol
   3 =======================
   4
   5 ..
   6   Licence: This work is licensed under the terms of the GNU GPL,
   7            version 2 or later. See the COPYING file in the top-level
   8            directory.
   9
  10 .. contents:: Table of Contents
  11
  12 Introduction
  13 ============
  14
  15 The vhost-user-gpu protocol is aiming at sharing the rendering result
  16 of a virtio-gpu, done from a vhost-user back-end process to a vhost-user
  17 front-end process (such as QEMU). It bears a resemblance to a display
  18 server protocol, if you consider QEMU as the display server and the
  19 back-end as the client, but in a very limited way. Typically, it will
  20 work by setting a scanout/display configuration, before sending flush
  21 events for the display updates. It will also update the cursor shape
  22 and position.
  23
  24 The protocol is sent over a UNIX domain stream socket, since it uses
  25 socket ancillary data to share opened file descriptors (DMABUF fds or
  26 shared memory). The socket is usually obtained via
  27 ``VHOST_USER_GPU_SET_SOCKET``.
  28
  29 Requests are sent by the *back-end*, and the optional replies by the
  30 *front-end*.
  31
  32 Wire format
  33 ===========
  34
  35 Unless specified differently, numbers are in the machine native byte
  36 order.
  37
  38 A vhost-user-gpu message (request and reply) consists of 3 header
  39 fields and a payload.
  40
  41 +---------+-------+------+---------+
  42 | request | flags | size | payload |
  43 +---------+-------+------+---------+
  44
  45 Header
  46 ------
  47
  48 :request: ``u32``, type of the request
  49
  50 :flags: ``u32``, 32-bit bit field:
  51
  52  - Bit 2 is the reply flag - needs to be set on each reply
  53
  54 :size: ``u32``, size of the payload
  55
  56 Payload types
  57 -------------
  58
  59 Depending on the request type, **payload** can be:
  60
  61 VhostUserGpuCursorPos
  62 ^^^^^^^^^^^^^^^^^^^^^
  63
  64 +------------+---+---+
  65 | scanout-id | x | y |
  66 +------------+---+---+
  67
  68 :scanout-id: ``u32``, the scanout where the cursor is located
  69
  70 :x/y: ``u32``, the cursor position
  71
  72 VhostUserGpuCursorUpdate
  73 ^^^^^^^^^^^^^^^^^^^^^^^^
  74
  75 +-----+-------+-------+--------+
  76 | pos | hot_x | hot_y | cursor |
  77 +-----+-------+-------+--------+
  78
  79 :pos: a ``VhostUserGpuCursorPos``, the cursor location
  80
  81 :hot_x/hot_y: ``u32``, the cursor hot location
  82
  83 :cursor: ``[u32; 64 * 64]``, 64x64 RGBA cursor data (PIXMAN_a8r8g8b8 format)
  84
  85 VhostUserGpuScanout
  86 ^^^^^^^^^^^^^^^^^^^
  87
  88 +------------+---+---+
  89 | scanout-id | w | h |
  90 +------------+---+---+
  91
  92 :scanout-id: ``u32``, the scanout configuration to set
  93
  94 :w/h: ``u32``, the scanout width/height size
  95
  96 VhostUserGpuUpdate
  97 ^^^^^^^^^^^^^^^^^^
  98
  99 +------------+---+---+---+---+------+
 100 | scanout-id | x | y | w | h | data |
 101 +------------+---+---+---+---+------+
 102
 103 :scanout-id: ``u32``, the scanout content to update
 104
 105 :x/y/w/h: ``u32``, region of the update
 106
 107 :data: RGB data (PIXMAN_x8r8g8b8 format)
 108
 109 VhostUserGpuDMABUFScanout
 110 ^^^^^^^^^^^^^^^^^^^^^^^^^
 111
 112 +------------+---+---+---+---+-----+-----+--------+-------+--------+
 113 | scanout-id | x | y | w | h | fdw | fwh | stride | flags | fourcc |
 114 +------------+---+---+---+---+-----+-----+--------+-------+--------+
 115
 116 :scanout-id: ``u32``, the scanout configuration to set
 117
 118 :x/y: ``u32``, the location of the scanout within the DMABUF
 119
 120 :w/h: ``u32``, the scanout width/height size
 121
 122 :fdw/fdh/stride/flags: ``u32``, the DMABUF width/height/stride/flags
 123
 124 :fourcc: ``i32``, the DMABUF fourcc
 125
 126
 127 VhostUserGpuEdidRequest
 128 ^^^^^^^^^^^^^^^^^^^^^^^
 129
 130 +------------+
 131 | scanout-id |
 132 +------------+
 133
 134 :scanout-id: ``u32``, the scanout to get edid from
 135
 136
 137 C structure
 138 -----------
 139
 140 In QEMU the vhost-user-gpu message is implemented with the following struct:
 141
 142 .. code:: c
 143
 144   typedef struct VhostUserGpuMsg {
 145       uint32_t request; /* VhostUserGpuRequest */
 146       uint32_t flags;
 147       uint32_t size; /* the following payload size */
 148       union {
 149           VhostUserGpuCursorPos cursor_pos;
 150           VhostUserGpuCursorUpdate cursor_update;
 151           VhostUserGpuScanout scanout;
 152           VhostUserGpuUpdate update;
 153           VhostUserGpuDMABUFScanout dmabuf_scanout;
 154           VhostUserGpuEdidRequest edid_req;
 155           struct virtio_gpu_resp_edid resp_edid;
 156           struct virtio_gpu_resp_display_info display_info;
 157           uint64_t u64;
 158       } payload;
 159   } QEMU_PACKED VhostUserGpuMsg;
 160
 161 Protocol features
 162 -----------------
 163
 164 .. code:: c
 165
 166   #define VHOST_USER_GPU_PROTOCOL_F_EDID 0
 167
 168 New messages and communication changes are negotiated thanks to the
 169 ``VHOST_USER_GPU_GET_PROTOCOL_FEATURES`` and
 170 ``VHOST_USER_GPU_SET_PROTOCOL_FEATURES`` requests.
 171
 172 Communication
 173 =============
 174
 175 Message types
 176 -------------
 177
 178 ``VHOST_USER_GPU_GET_PROTOCOL_FEATURES``
 179   :id: 1
 180   :request payload: N/A
 181   :reply payload: ``u64``
 182
 183   Get the supported protocol features bitmask.
 184
 185 ``VHOST_USER_GPU_SET_PROTOCOL_FEATURES``
 186   :id: 2
 187   :request payload: ``u64``
 188   :reply payload: N/A
 189
 190   Enable protocol features using a bitmask.
 191
 192 ``VHOST_USER_GPU_GET_DISPLAY_INFO``
 193   :id: 3
 194   :request payload: N/A
 195   :reply payload: ``struct virtio_gpu_resp_display_info`` (from virtio specification)
 196
 197   Get the preferred display configuration.
 198
 199 ``VHOST_USER_GPU_CURSOR_POS``
 200   :id: 4
 201   :request payload: ``VhostUserGpuCursorPos``
 202   :reply payload: N/A
 203
 204   Set/show the cursor position.
 205
 206 ``VHOST_USER_GPU_CURSOR_POS_HIDE``
 207   :id: 5
 208   :request payload: ``VhostUserGpuCursorPos``
 209   :reply payload: N/A
 210
 211   Set/hide the cursor.
 212
 213 ``VHOST_USER_GPU_CURSOR_UPDATE``
 214   :id: 6
 215   :request payload: ``VhostUserGpuCursorUpdate``
 216   :reply payload: N/A
 217
 218   Update the cursor shape and location.
 219
 220 ``VHOST_USER_GPU_SCANOUT``
 221   :id: 7
 222   :request payload: ``VhostUserGpuScanout``
 223   :reply payload: N/A
 224
 225   Set the scanout resolution. To disable a scanout, the dimensions
 226   width/height are set to 0.
 227
 228 ``VHOST_USER_GPU_UPDATE``
 229   :id: 8
 230   :request payload: ``VhostUserGpuUpdate``
 231   :reply payload: N/A
 232
 233   Update the scanout content. The data payload contains the graphical bits.
 234   The display should be flushed and presented.
 235
 236 ``VHOST_USER_GPU_DMABUF_SCANOUT``
 237   :id: 9
 238   :request payload: ``VhostUserGpuDMABUFScanout``
 239   :reply payload: N/A
 240
 241   Set the scanout resolution/configuration, and share a DMABUF file
 242   descriptor for the scanout content, which is passed as ancillary
 243   data. To disable a scanout, the dimensions width/height are set
 244   to 0, there is no file descriptor passed.
 245
 246 ``VHOST_USER_GPU_DMABUF_UPDATE``
 247   :id: 10
 248   :request payload: ``VhostUserGpuUpdate``
 249   :reply payload: empty payload
 250
 251   The display should be flushed and presented according to updated
 252   region from ``VhostUserGpuUpdate``.
 253
 254   Note: there is no data payload, since the scanout is shared thanks
 255   to DMABUF, that must have been set previously with
 256   ``VHOST_USER_GPU_DMABUF_SCANOUT``.
 257
 258 ``VHOST_USER_GPU_GET_EDID``
 259   :id: 11
 260   :request payload: ``struct VhostUserGpuEdidRequest``
 261   :reply payload: ``struct virtio_gpu_resp_edid`` (from virtio specification)
 262
 263   Retrieve the EDID data for a given scanout.
 264   This message requires the ``VHOST_USER_GPU_PROTOCOL_F_EDID`` protocol
 265   feature to be supported.