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iter14 α-16: env-gated OUTPUT bitstream byte dump pre-QBUF

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LIBVA_V4L2_DUMP_OUTPUT=<dir> writes source_data[0..slices_size] to
<dir>/output_p<profile>_s<surface>_t<ts>.bin immediately before
v4l2_queue_buffer OUTPUT. Discriminates whether libva writes the
correct H.264/HEVC bitstream bytes (same as kdirect/input file).

Off by default. Wrapped in static-cache env check.

iter11+12+13 confirmed Bug 4/5 are not in S_EXT_CTRLS payload, not
in kernel substrate (RFC v2), not in CPU cache visibility (α-17 sync
ioctl works but inert). The remaining libva-side surface is the
actual bitstream bytes the kernel reads.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
claude-noether
2026-05-14 08:19:29 +00:00
parent ca4dd88007
commit 522fb6daa5
1 changed files with 43 additions and 0 deletions
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src/picture.c
+43
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@@ -488,6 +488,49 @@ VAStatus RequestEndPicture(VADriverContextP context, VAContextID context_id)
if (rc != VA_STATUS_SUCCESS)
return rc;
/*
* iter14 α-16: env-gated dump of OUTPUT bitstream bytes immediately
* before QBUF. LIBVA_V4L2_DUMP_OUTPUT=<dir> writes source_data[0..
* slices_size] to <dir>/output_<profile>_<surface>_<frame>.bin.
* Discriminates whether libva writes the same H.264/HEVC slice bytes
* as kdirect — if YES, Bug 4/5 are not in the OUTPUT-side; if NO,
* narrow to which slice-write path produces the divergence.
*
* Off by default; no behavior change when env unset.
*/
{
static const char *dump_env = NULL;
static bool dump_env_checked = false;
if (!dump_env_checked) {
dump_env = getenv("LIBVA_V4L2_DUMP_OUTPUT");
dump_env_checked = true;
}
if (dump_env != NULL && dump_env[0] != '\0' &&
surface_object->source_data != NULL &&
surface_object->slices_size > 0) {
char path[256];
snprintf(path, sizeof(path),
"%s/output_p%d_s%u_t%llu.bin",
dump_env, (int)config_object->profile,
(unsigned int)surface_object->base.id,
(unsigned long long)context_object->timestamp_counter);
FILE *fp = fopen(path, "wb");
if (fp != NULL) {
size_t w = fwrite(surface_object->source_data,
1, surface_object->slices_size,
fp);
request_log("α-16: dumped %zu bytes to %s "
"(slices_count=%u)\n",
w, path,
surface_object->slices_count);
fclose(fp);
} else {
request_log("α-16: fopen(%s) failed: %s\n",
path, strerror(errno));
}
}
}
rc = v4l2_queue_buffer(driver_data->video_fd, -1, capture_type, NULL,
surface_object->destination_index, 0,
surface_object->destination_buffers_count);