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v4l2: log error_idx + failing ctrl id on S_EXT_CTRLS failure

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Better diagnostic when VIDIOC_S_EXT_CTRLS returns < 0: read
back error_idx and print which control id rejected (or
"ioctl-level" when error_idx == count, meaning the rejection
was generic, not per-control).

Made it possible to triage the daedalus_v4l2 phase 8.13 issue
by separating "the actual stateless control failed" (would
show failing_ctrl_id=0xa40a2c VP9_FRAME) from "libva probing
H264/HEVC profile/level we don't expose" (failing_ctrl_id=
0xa40900 H264_PROFILE etc.) — the latter is harmless on a
VP9-only context.

Before:
  v4l2-request: Unable to set control(s): Invalid argument

After (per-control):
  v4l2-request: Unable to set control(s): Invalid argument
                (error_idx=0/2 failing_ctrl_id=0xa40900 size=0)

After (ioctl-level):
  v4l2-request: Unable to set control(s): Invalid argument
                (error_idx=2/2 ioctl-level)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Markus Fritsche
2026-05-18 18:14:50 +00:00
parent 2146341460
commit de27e95571
1 changed files with 26 additions and 3 deletions
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src/v4l2.c
+26 -3
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@@ -476,12 +476,35 @@ int v4l2_set_controls(int video_fd, int request_fd,
struct v4l2_ext_control *control_array,
unsigned int num_controls)
{
struct v4l2_ext_controls controls;
int rc;
rc = v4l2_ioctl_controls(video_fd, request_fd, VIDIOC_S_EXT_CTRLS,
control_array, num_controls);
memset(&controls, 0, sizeof(controls));
controls.controls = control_array;
controls.count = num_controls;
if (request_fd >= 0) {
controls.which = V4L2_CTRL_WHICH_REQUEST_VAL;
controls.request_fd = request_fd;
}
rc = ioctl(video_fd, VIDIOC_S_EXT_CTRLS, &controls);
if (rc < 0) {
request_log("Unable to set control(s): %s\n", strerror(errno));
/* error_idx is the index of the first failing control;
* if it equals count, the ioctl itself failed (not a
* specific control payload). Useful for triaging
* which V4L2_CID_STATELESS_* the kernel rejected. */
if (controls.error_idx < num_controls)
request_log("Unable to set control(s): %s "
"(error_idx=%u/%u failing_ctrl_id=0x%x size=%u)\n",
strerror(errno),
controls.error_idx, controls.count,
control_array[controls.error_idx].id,
control_array[controls.error_idx].size);
else
request_log("Unable to set control(s): %s "
"(error_idx=%u/%u ioctl-level)\n",
strerror(errno),
controls.error_idx, controls.count);
return -1;
}