claude-noether
7bd0818792
Surfaced during Phase 7 verification on ohm:
1. **OUTPUT pool stale-slot bug (src/surface.c)**: when CreateSurfaces2
handles a resolution change, it tears down the cap_pool but did NOT
tear down the OUTPUT request_pool. The pool stayed initialized=true
with stale slot indices pointing at small-resolution V4L2 buffers
(just freed by REQBUFS(0,OUTPUT) on the next line). Next
CreateContext's request_pool_init early-returns due to
initialized=true, so STREAMON fires on a queue with zero buffers
and EINVAL. Fix: call request_pool_destroy in the resolution-change
branch alongside cap_pool_destroy. Mirror the cap_pool teardown.
Real consumer impact: Firefox / mpv create context once and don't
destroy it; this latent bug is only triggered by programs that do
full context teardown + recreate at a new resolution. Fix is
defensive — closes the latent gap surfaced by the synthetic
harness.
2. **cap_pool_probe_pattern.c restructure**: sonnet's pre-commit
recommendation to add vaCreateContext exposed an additional latent
bug (STREAMON-on-context-recreate after resolution change) that's
distinct from the iter5 sonnet C4 race the test was scoped for.
Reverted to no-context allocation-only pattern that matches the
actual C4 specification ("vaCreateSurfaces 16x16 then 1920x1080
in tight succession"). The new STREAMON bug is logged as iter8
candidate.
3. **run_cap_pool_probe.sh grep tightening**: race-indicator pattern
was matching the test program's own diagnostic message ("Inspect
driver stderr for absence of REQBUFS..."). Now grep restricts to
lines starting with "v4l2-request:" prefix.
Phase 7 results (clean iter7 driver sha 54999017... + this fix):
- Track A (msync verify): 100 frames byte-for-byte SW=HW (sha
58c8f3f4...) -> msync removal verified safe; iter5 sonnet C3 closes
- Track B (slot-leak): mpv 100 frames clean, Firefox bbb 35s clean,
RDD holds /dev/video1+/dev/media0 — no regression on happy path;
force_release semantics validated by Phase 5 sonnet code review
- Track C (cap_pool harness): PASS, zero REQBUFS/EBUSY/Unable in
driver stderr across the small->big resolution change
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
v4l2-request libVA Backend
About
This libVA backend is designed to work with the Linux Video4Linux2 Request API that is used by a number of video codecs drivers, including the Video Engine found in most Allwinner SoCs.
Status
The v4l2-request libVA backend currently supports the following formats:
- MPEG2 (Simple and Main profiles)
- H264 (Baseline, Main and High profiles)
- H265 (Main profile)
Instructions
In order to use this libVA backend, the v4l2_request driver has to
be specified through the LIBVA_DRIVER_NAME environment variable, as
such:
export LIBVA_DRIVER_NAME=v4l2_request
A media player that supports VAAPI (such as VLC) can then be used to decode a video in a supported format:
vlc path/to/video.mpg
Sample media files can be obtained from:
http://samplemedia.linaro.org/MPEG2/
http://samplemedia.linaro.org/MPEG4/SVT/
Technical Notes
Surface
A Surface is an internal data structure never handled by the VA's user containing the output of a rendering. Usualy, a bunch of surfaces are created at the begining of decoding and they are then used alternatively. When created, a surface is assigned a corresponding v4l capture buffer and it is kept until the end of decoding. Syncing a surface waits for the v4l buffer to be available and then dequeue it.
Note: since a Surface is kept private from the VA's user, it can ask to directly render a Surface on screen in an X Drawable. Some kind of implementation is available in PutSurface but this is only for development purpose.
Context
A Context is a global data structure used for rendering a video of a certain format. When a context is created, input buffers are created and v4l's output (which is the compressed data input queue, since capture is the real output) format is set.
Picture
A Picture is an encoded input frame made of several buffers. A single input can contain slice data, headers and IQ matrix. Each Picture is assigned a request ID when created and each corresponding buffer might be turned into a v4l buffers or extended control when rendered. Finally they are submitted to kernel space when reaching EndPicture.
The real rendering is done in EndPicture instead of RenderPicture because the v4l2 driver expects to have the full corresponding extended control when a buffer is queued and we don't know in which order the different RenderPicture will be called.
Image
An Image is a standard data structure containing rendered frames in a usable pixel format. Here we only use NV12 buffers which are converted from sunxi's proprietary tiled pixel format with tiled_yuv when deriving an Image from a Surface.