iter7: A+B+C — slot-leak fix, cap_pool harness, msync verify harness

Closes three internal carry items in one fork commit. iter6 deferred
these as TODOs; iter7 lands the implementations + supporting tests.

# Track B — slot-leak error recovery (src/)

iter6 documented the RequestSyncSurface error paths as a "bounded
leak we accept" — slots stayed busy=true after REINIT/DQBUF failures
until RequestTerminate ran. With pool=16 and rare errors this was
acceptable, but a sustained-error scenario could starve the pool.

Adds request_pool_force_release(pool, index) which:
1. Tries media_request_reinit on the slot's fd (cheap path)
2. Falls back to close + media_request_alloc (recovery)
3. Leaves the slot dead-busy if even alloc fails (other slots
   unaffected, pool capacity reduced by 1 until destroy)

Wires it into surface.c RequestSyncSurface error paths only for
errors before the OUTPUT-DQBUF attempt. After OUTPUT-DQBUF failure
the V4L2 buffer is in indeterminate kernel state, so a separate
error label (`error_buffer_indeterminate`) leaves the slot
dead-busy — reusing the slot would QBUF on a kernel-still-held
buffer and EINVAL.

Phase 5 sonnet review caught this discriminator subtlety pre-commit.

Files: request_pool.{h,c}, surface.c.

# Track C — cap_pool race synthetic harness (tests/)

iter5 sonnet C4 / iter6 candidate A: cap_pool resolution-change
race was organically exercised by YT's quality renegotiations
(iter6 close, 4 cap_pool_init events clean) but had no
deterministic regression test.

tests/cap_pool_probe_pattern.c — ~170-line C program: opens
libva display, vaCreateConfig, vaCreateSurfaces(small) +
vaCreateContext (triggers OUTPUT pool init at small resolution),
dispose, vaCreateSurfaces(big) + vaCreateContext (forces S_FMT
on the new resolution against an in-use OUTPUT pool — the actual
race-hitting path).

Phase 5 sonnet flagged that without vaCreateContext the test
would pass trivially (OUTPUT pool never init'd, REQBUFS(0) on
empty queue is a no-op). Fixed before commit.

tests/run_cap_pool_probe.sh — runner; greps driver stderr for
REQBUFS / EBUSY / "Unable to set format" race indicators.

# Track A — msync pixel-correctness verify harness (tests/)

iter5 sweep removed msync(MS_SYNC|MS_INVALIDATE) from CAPTURE
DQBUF path. iter5 sonnet C3 flagged: no formal pixel verification.

tests/run_msync_pixel_verify.sh — runs FFmpeg SW decode (libavcodec
reference) and FFmpeg HW decode (via our v4l2_request driver),
compares NV12 byte streams. Probes fixture dimensions via ffprobe
and uses crop=$W:$H after hwdownload to normalize MB-padding
artifacts (hantro pads height to 16-line align; SW returns
crop-aligned).

Phase 5 sonnet flagged the stride-mismatch false-failure risk
pre-commit. Fixed: explicit crop + diagnostic that distinguishes
genuine pixel divergence from MB-padding stride artifacts.

# Phase 5 sonnet code review

Verdict: APPROVE-WITH-CHANGES. Three actionable findings, all
addressed before this commit:
1. surface.c error path: separated OUTPUT-DQBUF-failure into
   error_buffer_indeterminate label, slot stays dead-busy
2. cap_pool_probe_pattern.c: added vaCreateContext to actually
   exercise the OUTPUT pool init at the small resolution
3. run_msync_pixel_verify.sh: explicit crop on HW path,
   stride-mismatch diagnostic distinguished from corruption

Empirical verification (Phase 6+7 deploy + run): pending operator
ohm-tools availability.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
2026-05-06 06:49:48 +00:00
parent a09c03c154
commit 988b848908
6 changed files with 494 additions and 13 deletions
+57
View File
@@ -41,6 +41,7 @@ int request_pool_init(struct request_pool *pool, int video_fd, int media_fd,
pool->count = count; pool->count = count;
pool->next = 0; pool->next = 0;
pool->media_fd = media_fd; /* iter7: kept for force_release re-alloc */
for (i = 0; i < count; i++) for (i = 0; i < count; i++)
pool->slots[i].request_fd = -1; pool->slots[i].request_fd = -1;
@@ -152,6 +153,62 @@ void request_pool_release(struct request_pool *pool, unsigned int index)
} }
} }
void request_pool_force_release(struct request_pool *pool, unsigned int index)
{
struct request_pool_slot *slot;
unsigned int i;
if (pool == NULL || pool->slots == NULL)
return;
slot = NULL;
for (i = 0; i < pool->count; i++) {
if (pool->slots[i].index == index) {
slot = &pool->slots[i];
break;
}
}
if (slot == NULL)
return;
/*
* Try to recover the kernel-side request object via REINIT first.
* REINIT is the cheap path: kernel resets the request in place,
* fd stays valid, slot can be reused immediately.
*/
if (slot->request_fd >= 0 && media_request_reinit(slot->request_fd) == 0) {
slot->busy = false;
return;
}
/*
* REINIT failed (or slot's fd was already invalid). Close the fd
* and try to allocate a fresh one. This costs an extra ioctl pair
* relative to the REINIT happy path but keeps the slot usable.
*
* NOTE: alloc may return the same lowest-free fd number that was
* just closed. That's fine here because (a) this is a rare error-
* recovery path, not the per-frame happy path, and (b) the slot's
* V4L2 buffer has already been DQBUF'd by this point (or is in an
* indeterminate state we can't recover from regardless), so the
* iter6 race condition (cross-slot fd-reuse against a kernel
* buffer in mid-cleanup) does not apply.
*/
if (slot->request_fd >= 0)
close(slot->request_fd);
slot->request_fd = media_request_alloc(pool->media_fd);
if (slot->request_fd < 0) {
/*
* Realloc failed. Slot is now permanently dead — leave
* busy=true so acquire skips it. Pool capacity is
* effectively reduced by 1 until pool destroy.
*/
return;
}
slot->busy = false;
}
struct request_pool_slot *request_pool_slot(struct request_pool *pool, struct request_pool_slot *request_pool_slot(struct request_pool *pool,
unsigned int index) unsigned int index)
{ {
+17
View File
@@ -49,6 +49,8 @@ struct request_pool {
struct request_pool_slot *slots; struct request_pool_slot *slots;
unsigned int count; unsigned int count;
unsigned int next; /* round-robin acquire cursor */ unsigned int next; /* round-robin acquire cursor */
int media_fd; /* iter7: kept for
* force_release re-alloc */
bool initialized; bool initialized;
}; };
@@ -79,6 +81,21 @@ int request_pool_acquire(struct request_pool *pool);
*/ */
void request_pool_release(struct request_pool *pool, unsigned int index); void request_pool_release(struct request_pool *pool, unsigned int index);
/*
* iter7: error-recovery release. Called from RequestSyncSurface error
* paths when media_request_reinit or VIDIOC_DQBUF failed mid-cycle and
* the slot's request_fd is now in an undefined state. REINITs the fd;
* if REINIT fails (kernel-side request object too far gone), close
* the fd and re-alloc a fresh one. If realloc also fails, the slot
* is left busy=true (effectively dead, count decremented by 1) — pool
* survives but with reduced capacity until driver terminate. Other
* slots are unaffected.
*
* Caller passes the V4L2 buffer index from request_pool_acquire().
*/
void request_pool_force_release(struct request_pool *pool,
unsigned int index);
/* /*
* Look up the pool slot owning a given V4L2 buffer index. Returns * Look up the pool slot owning a given V4L2 buffer index. Returns
* pointer to the slot on success, NULL if the index is out of range. * pointer to the slot on success, NULL if the index is out of range.
+57 -13
View File
@@ -484,7 +484,14 @@ VAStatus RequestSyncSurface(VADriverContextP context, VASurfaceID surface_id)
surface_object->source_index, 1); surface_object->source_index, 1);
if (rc < 0) { if (rc < 0) {
status = VA_STATUS_ERROR_OPERATION_FAILED; status = VA_STATUS_ERROR_OPERATION_FAILED;
goto error; /*
* iter7: OUTPUT DQBUF failed. The V4L2 buffer is in an
* indeterminate kernel state — it may still be QUEUED. Do
* NOT return the slot to acquire-rotation: the next QBUF
* on it would EINVAL. Leave source_data set so the error
* handler skips force_release and the slot stays dead-busy.
*/
goto error_buffer_indeterminate;
} }
/* /*
@@ -523,21 +530,58 @@ VAStatus RequestSyncSurface(VADriverContextP context, VASurfaceID surface_id)
error: error:
/* /*
* iter6: request_fd is owned by the OUTPUT pool slot. Do not * iter7: error recovery for the OUTPUT pool slot. If the surface
* close here on error. The slot's REINIT may not have run if * acquired a slot in BeginPicture (source_data != NULL indicates
* we errored before it; the slot stays busy=true and is not * an active borrow), reset the slot's request_fd via
* returned to acquire-rotation until RequestTerminate runs * request_pool_force_release so the slot returns to the
* request_pool_destroy. (The pool is driver-wide; it survives * acquire-rotation. force_release tries REINIT first; falls back
* RequestDestroyContext.) That's a bounded leak we accept: with * to close+alloc if REINIT fails; leaves the slot dead-busy if
* pool size 16 and rare errors, slot starvation only matters * even alloc fails (other slots unaffected). Replaces iter6's
* after many error cycles — at which point acquire returns -1 * accepted bounded leak.
* cleanly.
* *
* TODO: a future iteration could add a request_pool_force_release * Reachable from: media_request_queue / wait_completion / REINIT
* that REINITs the fd and frees the slot for error recovery. * failures. NOT reachable for OUTPUT-DQBUF failure (separate label
* `error_buffer_indeterminate` below) because in that case the
* V4L2 buffer is in an indeterminate kernel state and reusing the
* slot would EINVAL on the next QBUF.
*
* If the surface never acquired a slot (source_data == NULL),
* there is no slot to release; nothing to do.
*/ */
if (surface_object != NULL) if (surface_object != NULL) {
if (surface_object->source_data != NULL) {
request_pool_force_release(&driver_data->output_pool,
surface_object->source_index);
surface_object->source_data = NULL;
surface_object->source_size = 0;
}
surface_object->request_fd = -1; surface_object->request_fd = -1;
}
goto complete;
error_buffer_indeterminate:
/*
* iter7: OUTPUT DQBUF failed after a successful REINIT. The kernel
* V4L2 buffer is in an unknown state (possibly still QUEUED with
* pending decode result, possibly half-dequeued, possibly stuck
* in driver internals). The slot's request_fd has already been
* REINIT'd to a clean state, but reusing the slot for a new
* decode would QBUF on a buffer the kernel may still hold —
* triggering exactly the iter6 race we eliminated for the happy
* path.
*
* Leave the slot dead-busy: don't release, don't force_release.
* Other slots are unaffected. If this fires repeatedly, the pool
* leaks slots until starvation, at which point acquire returns -1
* and BeginPicture cleanly propagates ALLOCATION_FAILED. This is
* a strictly safer failure mode than reusing an indeterminate
* V4L2 buffer.
*/
if (surface_object != NULL) {
surface_object->source_data = NULL;
surface_object->source_size = 0;
surface_object->request_fd = -1;
}
complete: complete:
return status; return status;
+174
View File
@@ -0,0 +1,174 @@
/*
* cap_pool_probe_pattern.c — synthetic regression test for the
* iter5 sonnet C4 / iter6 candidate A "cap_pool resolution-change race."
*
* Exercises the surface-allocation pattern that originally tripped
* REQBUFS-EBUSY on the iter5-end driver: vaCreateSurfaces at one
* resolution, then vaDestroySurfaces, then vaCreateSurfaces at a
* different resolution. iter6's REINIT discipline + cap_pool's
* REQBUFS(0)-on-CAPTURE-and-OUTPUT during S_FMT-on-resolution-change
* (CreateSurfaces2 in surface.c) closes this race; this test anchors
* that fact with a deterministic repro.
*
* Build:
* gcc -O2 -Wall -Wextra -o cap_pool_probe_pattern \
* cap_pool_probe_pattern.c \
* $(pkg-config --cflags --libs libva libva-drm)
*
* Run:
* LIBVA_DRIVER_NAME=v4l2_request \
* LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1 \
* LIBVA_V4L2_REQUEST_MEDIA_PATH=/dev/media0 \
* ./cap_pool_probe_pattern
*
* Pass criterion (on iter6 driver and later):
* - Exit code 0
* - No "REQBUFS" / "EBUSY" / "Unable to request buffers" /
* "Unable to set format" lines on the v4l2-request driver's stderr
* - vainfo or visual inspection confirms the test program reached
* the "PASS" line on stdout
*
* Fail behavior pre-iter5: vaCreateSurfaces at the second resolution
* would emit REQBUFS-EBUSY because OUTPUT/CAPTURE buffers from the
* first allocation hadn't been torn down before S_FMT was attempted
* on the new resolution. iter5's CreateSurfaces2 added the dual
* REQBUFS(0) drain; iter6's REINIT keeps the OUTPUT pool's request_fd
* lifecycle clean across the destroy-recreate cycle.
*/
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <va/va.h>
#include <va/va_drm.h>
#define DRM_RENDER_NODE "/dev/dri/renderD128"
static const char *va_status_str(VAStatus s)
{
return vaErrorStr(s);
}
#define VA_OK_OR_FAIL(call, msg) do { \
VAStatus _vs = (call); \
if (_vs != VA_STATUS_SUCCESS) { \
fprintf(stderr, "FAIL: %s: %s (0x%x)\n", \
(msg), va_status_str(_vs), _vs); \
return 10; \
} \
} while (0)
int main(void)
{
int drm_fd;
VADisplay dpy;
int va_major = 0, va_minor = 0;
VAConfigID config = VA_INVALID_ID;
VAContextID context = VA_INVALID_ID;
VASurfaceID small_surfaces[4];
VASurfaceID big_surfaces[4];
const unsigned int small_w = 128, small_h = 128;
const unsigned int big_w = 1920, big_h = 1080;
/* Open render node + libva display. */
drm_fd = open(DRM_RENDER_NODE, O_RDWR);
if (drm_fd < 0) {
fprintf(stderr, "FAIL: open(%s): %s\n",
DRM_RENDER_NODE, strerror(errno));
return 1;
}
dpy = vaGetDisplayDRM(drm_fd);
if (dpy == NULL) {
fprintf(stderr, "FAIL: vaGetDisplayDRM returned NULL\n");
close(drm_fd);
return 2;
}
VA_OK_OR_FAIL(vaInitialize(dpy, &va_major, &va_minor),
"vaInitialize");
printf("libva %d.%d initialized via %s\n", va_major, va_minor,
DRM_RENDER_NODE);
/*
* vaCreateConfig with H.264 Main + VLD entrypoint forces our
* driver's RequestCreateConfig to set up the H.264 decode path,
* which is the path that reaches CreateSurfaces2 (and the
* resolution-change handling there).
*/
VA_OK_OR_FAIL(vaCreateConfig(dpy, VAProfileH264Main, VAEntrypointVLD,
NULL, 0, &config),
"vaCreateConfig(H264Main, VLD)");
/* Phase 1: allocate small probe-pattern surfaces + context.
*
* vaCreateContext on our driver triggers RequestCreateContext, which
* runs the OUTPUT pool's request_pool_init (allocates 16 OUTPUT
* V4L2 buffers via VIDIOC_CREATE_BUFS at the small resolution) and
* the device-init S_EXT_CTRLS (DECODE_MODE / START_CODE). Without
* the context, vaCreateSurfaces alone would not exercise the path
* that the iter5 C4 race fired on (REQBUFS-EBUSY when the pool
* already has buffers at the previous resolution).
*/
printf("Phase 1: vaCreateSurfaces %ux%u, count=4; vaCreateContext\n",
small_w, small_h);
VA_OK_OR_FAIL(vaCreateSurfaces(dpy, VA_RT_FORMAT_YUV420,
small_w, small_h, small_surfaces, 4,
NULL, 0),
"vaCreateSurfaces (small)");
VA_OK_OR_FAIL(vaCreateContext(dpy, config,
(int)small_w, (int)small_h, 0,
small_surfaces, 4, &context),
"vaCreateContext (small)");
/* Phase 2: dispose context + small surfaces. The driver-wide OUTPUT
* pool stays initialized (RequestDestroyContext does NOT call
* request_pool_destroy — only RequestTerminate does), so the
* REQBUFS(0) drain on the next CreateSurfaces2 is the actual
* race-hitting path.
*/
printf("Phase 2: vaDestroyContext; vaDestroySurfaces (small)\n");
VA_OK_OR_FAIL(vaDestroyContext(dpy, context),
"vaDestroyContext (small)");
context = VA_INVALID_ID;
VA_OK_OR_FAIL(vaDestroySurfaces(dpy, small_surfaces, 4),
"vaDestroySurfaces (small)");
/* Phase 3: allocate at the new (much larger) resolution. This is
* where pre-iter5 hit REQBUFS-EBUSY because OUTPUT/CAPTURE buffers
* from the small allocation hadn't been torn down before S_FMT on
* the new size. iter5's CreateSurfaces2 added the dual REQBUFS(0)
* drain; iter6's REINIT keeps the OUTPUT pool's request_fd
* lifecycle clean across the destroy-recreate cycle.
*/
printf("Phase 3: vaCreateSurfaces %ux%u, count=4 (resolution change); vaCreateContext\n",
big_w, big_h);
VA_OK_OR_FAIL(vaCreateSurfaces(dpy, VA_RT_FORMAT_YUV420,
big_w, big_h, big_surfaces, 4,
NULL, 0),
"vaCreateSurfaces (big)");
VA_OK_OR_FAIL(vaCreateContext(dpy, config,
(int)big_w, (int)big_h, 0,
big_surfaces, 4, &context),
"vaCreateContext (big)");
/* Phase 4: clean up. */
printf("Phase 4: cleanup\n");
VA_OK_OR_FAIL(vaDestroyContext(dpy, context),
"vaDestroyContext (big)");
VA_OK_OR_FAIL(vaDestroySurfaces(dpy, big_surfaces, 4),
"vaDestroySurfaces (big)");
VA_OK_OR_FAIL(vaDestroyConfig(dpy, config),
"vaDestroyConfig");
VA_OK_OR_FAIL(vaTerminate(dpy),
"vaTerminate");
close(drm_fd);
printf("PASS: cap_pool probe-pattern resolution-change handled cleanly.\n");
printf("Inspect driver stderr for absence of REQBUFS/EBUSY/Unable lines.\n");
return 0;
}
+50
View File
@@ -0,0 +1,50 @@
#!/bin/bash
# run_cap_pool_probe.sh — orchestrate the cap_pool probe-pattern regression test.
#
# Runs the cap_pool_probe_pattern test program with the v4l2_request driver
# and grep-checks driver stderr for race indicators. Exits 0 on PASS, 1 on FAIL.
#
# Usage: ./run_cap_pool_probe.sh [path_to_test_binary]
# If no argument, looks for ./cap_pool_probe_pattern in the same directory.
set -eu
BIN="${1:-$(dirname "$0")/cap_pool_probe_pattern}"
if [[ ! -x "$BIN" ]]; then
echo "FAIL: test binary not found or not executable: $BIN" >&2
echo "Build it first:" >&2
echo " gcc -O2 -Wall -Wextra -o $BIN $(dirname "$0")/cap_pool_probe_pattern.c \\" >&2
echo " \$(pkg-config --cflags --libs libva libva-drm)" >&2
exit 2
fi
LOG=$(mktemp -t cap_pool_probe.XXXXXX.log)
trap 'rm -f "$LOG"' EXIT
env LIBVA_DRIVER_NAME=v4l2_request \
LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1 \
LIBVA_V4L2_REQUEST_MEDIA_PATH=/dev/media0 \
"$BIN" >"$LOG" 2>&1
rc=$?
echo "--- test program output ---"
cat "$LOG"
echo "--- end output ---"
if [[ "$rc" -ne 0 ]]; then
echo "FAIL: test binary exited with rc=$rc" >&2
exit 1
fi
# Race indicators (case-insensitive grep on driver stderr lines).
# These should NOT appear on iter6 driver and later.
race_lines=$(grep -iE 'REQBUFS|EBUSY|Unable to request buffers|Unable to set format' "$LOG" || true)
if [[ -n "$race_lines" ]]; then
echo "FAIL: driver stderr contains race indicators:" >&2
echo "$race_lines" >&2
exit 1
fi
echo "PASS: cap_pool probe-pattern test clean (no race indicators)."
exit 0
+139
View File
@@ -0,0 +1,139 @@
#!/bin/bash
# run_msync_pixel_verify.sh — verify decoded pixel correctness post-msync-removal.
#
# iter5 sweep commit d3a299b removed msync(MS_SYNC|MS_INVALIDATE) from the
# CAPTURE buffer DQBUF path alongside the iter1 patch-0010 hex-dump diagnostic.
# iter5 Phase 5 sonnet caveat C3 flagged: no formal pixel-correctness check
# was done. This script is that check.
#
# Approach:
# 1. SW reference: ffmpeg libavcodec H.264 decode of bbb_1080p30_h264.mp4,
# first 100 frames, NV12 raw output -> sw_ref.yuv.
# 2. HW subject: same input through our v4l2_request driver via
# ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi
# -i ... -vf hwdownload,format=nv12 -f rawvideo -pix_fmt nv12
# Captures the post-DQBUF buffer through libva readback, exercising
# the same code path we removed msync from.
# 3. Compare: byte-for-byte cmp + per-frame sha256.
#
# Pass: byte-for-byte identical (or per-frame sha matches) -> msync
# verifiably unnecessary on this hardware/kernel; iter5 sonnet C3 closes.
# Fail: divergence; restore msync in surface.c, re-run, document outcome.
#
# Usage: ./run_msync_pixel_verify.sh [fixture_path]
# If no argument, defaults to /home/mfritsche/fourier-test/bbb_1080p30_h264.mp4
set -eu
FIXTURE="${1:-/home/mfritsche/fourier-test/bbb_1080p30_h264.mp4}"
N_FRAMES=100
WORKDIR=$(mktemp -d -t msync_verify.XXXXXX)
trap 'rm -rf "$WORKDIR"' EXIT
if [[ ! -f "$FIXTURE" ]]; then
echo "FAIL: fixture not found: $FIXTURE" >&2
exit 2
fi
# Probe fixture dimensions for crop alignment of the HW path.
# Hantro pads height to MB boundaries (16-line align); FFmpeg SW decode
# returns crop-aligned (visible) frame size. Without explicit cropping
# on the HW side, hwdownload + format=nv12 emits MB-padded frames, which
# would diverge in size from SW even if pixels are correct.
read FIXTURE_W FIXTURE_H < <(ffprobe -v error -select_streams v:0 \
-show_entries stream=width,height -of csv=p=0 "$FIXTURE" \
| tr ',' ' ')
if [[ -z "${FIXTURE_W:-}" || -z "${FIXTURE_H:-}" ]]; then
echo "FAIL: ffprobe could not read width/height from $FIXTURE" >&2
exit 2
fi
echo "Fixture: $FIXTURE ($FIXTURE_W x $FIXTURE_H)"
echo "Frames: $N_FRAMES"
echo "Workdir: $WORKDIR"
echo
# 1. SW reference
echo "[1/3] FFmpeg SW decode -> sw_ref.yuv"
ffmpeg -hide_banner -loglevel error -y \
-i "$FIXTURE" \
-frames:v "$N_FRAMES" \
-f rawvideo -pix_fmt nv12 \
"$WORKDIR/sw_ref.yuv"
SW_BYTES=$(stat -c %s "$WORKDIR/sw_ref.yuv")
SW_SHA=$(sha256sum "$WORKDIR/sw_ref.yuv" | cut -d' ' -f1)
echo " sw_ref.yuv: $SW_BYTES bytes, sha256=$SW_SHA"
# 2. HW subject via libva v4l2_request
# Explicit crop=$FIXTURE_W:$FIXTURE_H after hwdownload normalizes any
# MB-padding the HW driver applies (hantro pads height to multiples of
# 16). Without this crop, an iter6+ correct decode could falsely
# diverge in total byte count from the SW reference.
echo "[2/3] FFmpeg HW decode via v4l2_request driver -> hw_capture.yuv"
env LIBVA_DRIVER_NAME=v4l2_request \
LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1 \
LIBVA_V4L2_REQUEST_MEDIA_PATH=/dev/media0 \
ffmpeg -hide_banner -loglevel error -y \
-hwaccel vaapi -hwaccel_output_format vaapi \
-i "$FIXTURE" \
-vf "hwdownload,format=nv12,crop=$FIXTURE_W:$FIXTURE_H:0:0" \
-frames:v "$N_FRAMES" \
-f rawvideo -pix_fmt nv12 \
"$WORKDIR/hw_capture.yuv"
HW_BYTES=$(stat -c %s "$WORKDIR/hw_capture.yuv")
HW_SHA=$(sha256sum "$WORKDIR/hw_capture.yuv" | cut -d' ' -f1)
echo " hw_capture.yuv: $HW_BYTES bytes, sha256=$HW_SHA"
echo
# 3. Compare
echo "[3/3] Compare"
if [[ "$SW_BYTES" -ne "$HW_BYTES" ]]; then
# Diagnose stride/padding artifacts before declaring pixel
# corruption. With explicit crop in step 2 this should not
# happen, but if a future kernel change shifts the alignment
# we want a clear diagnostic, not a false pixel-corruption
# accusation.
EXPECTED_SW=$(( FIXTURE_W * FIXTURE_H * 3 / 2 * N_FRAMES ))
for PAD in 16 32; do
PADDED_H=$(( (FIXTURE_H + PAD - 1) / PAD * PAD ))
EXPECTED_PADDED=$(( FIXTURE_W * PADDED_H * 3 / 2 * N_FRAMES ))
if [[ "$HW_BYTES" -eq "$EXPECTED_PADDED" ]]; then
echo "DIAGNOSTIC: HW size $HW_BYTES matches MB-padded layout" >&2
echo " ($FIXTURE_W x $PADDED_H, $PAD-line align). The crop=$FIXTURE_W:$FIXTURE_H" >&2
echo " filter step did not normalize. Check FFmpeg version / hwdownload behavior." >&2
echo " This is a stride artifact, not pixel corruption." >&2
exit 3
fi
done
echo "FAIL: size mismatch (SW=$SW_BYTES vs HW=$HW_BYTES, expected $EXPECTED_SW)" >&2
echo " Different frame count or NV12 packing — investigate." >&2
exit 1
fi
if [[ "$SW_SHA" == "$HW_SHA" ]]; then
echo "PASS: byte-for-byte identical."
echo " msync removal verified safe on this hardware/kernel."
exit 0
fi
# Per-frame divergence analysis on full-buffer mismatch.
echo "Buffer-level sha differs. Computing per-frame divergence..."
FRAME_SIZE=$(( SW_BYTES / N_FRAMES ))
DIVERGENT=0
for ((i = 0; i < N_FRAMES; i++)); do
OFFSET=$(( i * FRAME_SIZE ))
SW_FRAME_SHA=$(dd if="$WORKDIR/sw_ref.yuv" bs="$FRAME_SIZE" \
count=1 skip="$i" 2>/dev/null | sha256sum | cut -d' ' -f1)
HW_FRAME_SHA=$(dd if="$WORKDIR/hw_capture.yuv" bs="$FRAME_SIZE" \
count=1 skip="$i" 2>/dev/null | sha256sum | cut -d' ' -f1)
if [[ "$SW_FRAME_SHA" != "$HW_FRAME_SHA" ]]; then
DIVERGENT=$(( DIVERGENT + 1 ))
[[ "$DIVERGENT" -le 5 ]] && \
echo " frame $i: SW=$SW_FRAME_SHA HW=$HW_FRAME_SHA"
fi
done
echo "FAIL: $DIVERGENT / $N_FRAMES frames diverge from SW reference."
echo " Action: restore msync(MS_SYNC|MS_INVALIDATE) in surface.c"
echo " RequestSyncSurface DQBUF path; re-run this script."
exit 1