marfrit/libva-v4l2-request-fourier
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v4l2: add QUERYCTRL/QUERYMENU capability-probe helpers

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Pure utility additions, no behaviour change. Three helpers in
src/v4l2.{c,h}:

  - v4l2_query_ext_ctrl(): wraps VIDIOC_QUERY_EXT_CTRL by CID.
    Returns 0 if the control exists, -1 if not. Caller passes NULL
    qec to test existence only.

  - v4l2_query_menu(): wraps VIDIOC_QUERYMENU at a given index.
    Returns 0 if a menu item exists at that index, -1 otherwise.

  - v4l2_ctrl_menu_has_value(): convenience layered on the above.
    For a menu/intmenu-type control, walks all menu items between
    minimum and maximum and returns true iff `value` is a valid
    entry. Used by callers that ask "does this driver accept menu
    value X for this CID?" without caring about iteration details.

These unblock commit 3 (request_pool — needs ext-ctrl probing for
codec-ops dispatch) and commit 4 (probe-then-set DECODE_MODE/
START_CODE — replaces 0002's unconditional set with a real probe)
of the upstreamable design's six-commit series.

Forward-declarations in v4l2.h keep the header lean: existing
prototypes already use opaque struct v4l2_ext_control * pointers
without including <linux/videodev2.h>; we follow the same
convention for struct v4l2_query_ext_ctrl and struct v4l2_querymenu.

No call sites added in this commit. Compile-only verification:
the .so links cleanly with three new exports.

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 50e0c2b996
commit 58a0e8baf9
2 changed files with 93 additions and 0 deletions
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src/v4l2.h
+33
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@@ -64,4 +64,37 @@ int v4l2_set_control(int video_fd, int request_fd, unsigned int id, void *data,
unsigned int size);
int v4l2_set_stream(int video_fd, unsigned int type, bool enable);
/*
* Capability-probe helpers. These let calling code discover what the
* backing kernel driver supports rather than hardcoding assumptions
* about specific decoder hardware.
*/
/*
* Query the metadata of an extended control by CID. Fills *qec on
* success. Returns 0 if the control exists, -1 (errno=EINVAL) if the
* driver does not expose this CID. Pass qec=NULL to test existence
* only.
*/
struct v4l2_query_ext_ctrl;
int v4l2_query_ext_ctrl(int video_fd, unsigned int id,
struct v4l2_query_ext_ctrl *qec);
/*
* Query a single menu item of a menu/intmenu control at the given
* index. Fills *qm on success. Returns 0 if the menu item exists at
* this index, -1 otherwise.
*/
struct v4l2_querymenu;
int v4l2_query_menu(int video_fd, unsigned int id, unsigned int index,
struct v4l2_querymenu *qm);
/*
* Convenience: for a menu-type control, return true iff `value` is a
* valid menu entry (i.e. the driver accepts it). Walks all menu items
* up to the control's maximum to check.
*/
bool v4l2_ctrl_menu_has_value(int video_fd, unsigned int id,
unsigned int value);
#endif