marfrit/libva-v4l2-request-fourier
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context: introduce request_pool, decouple OUTPUT buffers from surfaces

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Commit 3 of the upstreamable plan (upstreamable_design.md §1, §5).
Replaces the prior per-surface OUTPUT-buffer ownership model with a
small driver-wide pool sized by codec pipeline depth (4 H.264 frames
in flight), allocated unconditionally regardless of caller's
num_render_targets.

Prior art (kernel UAPI dev-stateless-decoder.rst, ffmpeg
v4l2_request.c, Chromium V4L2StatelessVideoDecoder, GStreamer
v4l2slh264dec) all decouple OUTPUT and CAPTURE pool sizing. fourier's
"output_count == surfaces_count" model was a category error: OUTPUT
buffers are request-time bitstream slots, CAPTURE buffers are
picture-time DPB slots; their lifecycles and sizing are independent.

Changes:
  * NEW src/request_pool.{c,h} (~200 LoC):
      - request_pool_init(): CREATE_BUFS + per-slot QUERYBUF + mmap.
      - request_pool_destroy(): munmap all, idempotent.
      - request_pool_acquire(): round-robin claim; returns V4L2 buffer
        index of an unused slot or -1.
      - request_pool_release(): mark slot free for reuse.
      - request_pool_slot(): accessor for ptr/size given a buffer index.

  * src/request.h: add struct request_pool output_pool to request_data.

  * src/context.c::RequestCreateContext: replace the per-surface
    OUTPUT loop with a single request_pool_init() call (count=4,
    independent of surfaces_count). Drop the now-unused locals
    (length, offset, source_data, output_buffers_count, index,
    index_base, i, surface_object). DELETES patch 0002's
    "output_buffers_count = ... ? ... : 4" hack inline — the pool's
    own count parameter supersedes it.

  * src/picture.c::RequestBeginPicture: borrow a pool slot at frame
    start, write its mmap pointer/size/index into the surface's
    transient source_* fields. The fields stay (still useful as
    a borrow handle that the existing codec_store_buffer memcpys
    target), but no longer represent surface-permanent ownership.
    Reset slices_size/slices_count here too (was implicit on first
    Render).

  * src/surface.c::RequestSyncSurface: after VIDIOC_DQBUF returns
    the OUTPUT buffer, release the pool slot and clear the surface's
    borrow handle. Fixes the segv on second-frame submission.

  * src/surface.c::RequestDestroySurfaces: remove the munmap of
    source_data — pool owns the mmap.

  * src/request.c::RequestTerminate: call request_pool_destroy()
    before close(video_fd) so munmaps still target a valid fd.

  * src/meson.build: add request_pool.c and request_pool.h to the
    sources/headers lists.

This commit removes 0002's OUTPUT-pool hack inline (the
"floor to 4" line is gone). The DECODE_MODE/START_CODE block in 0002
remains until commit 4 lands.

Build-verified clean on aarch64.

Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>
This commit is contained in:
Markus Fritsche
2026-05-01 12:00:00 +00:00
parent 58a0e8baf9
commit 565f5c0de4
8 changed files with 307 additions and 53 deletions
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src/picture.c
+27
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@@ -216,6 +216,8 @@ VAStatus RequestBeginPicture(VADriverContextP context, VAContextID context_id,
struct request_data *driver_data = context->pDriverData;
struct object_context *context_object;
struct object_surface *surface_object;
struct request_pool_slot *slot;
int slot_index;
context_object = CONTEXT(driver_data, context_id);
if (context_object == NULL)
@@ -228,6 +230,31 @@ VAStatus RequestBeginPicture(VADriverContextP context, VAContextID context_id,
if (surface_object->status == VASurfaceRendering)
RequestSyncSurface(context, surface_id);
/*
* Borrow an OUTPUT (bitstream-input) slot from the driver-wide
* pool for the duration of this Begin/Render/End cycle. The
* surface's source_* fields hold the borrow's mmap pointer/size/
* V4L2 buffer index until RequestSyncSurface releases it after
* VIDIOC_DQBUF.
*/
slot_index = request_pool_acquire(&driver_data->output_pool);
if (slot_index < 0)
return VA_STATUS_ERROR_ALLOCATION_FAILED;
slot = request_pool_slot(&driver_data->output_pool,
(unsigned int)slot_index);
if (slot == NULL) {
request_pool_release(&driver_data->output_pool,
(unsigned int)slot_index);
return VA_STATUS_ERROR_ALLOCATION_FAILED;
}
surface_object->source_index = slot->index;
surface_object->source_data = slot->data;
surface_object->source_size = slot->size;
surface_object->slices_size = 0;
surface_object->slices_count = 0;
surface_object->status = VASurfaceRendering;
context_object->render_surface_id = surface_id;