It would be useful to mark instances of v4l2_subdev_state structures as const when code needs to access them read-only. This isn't currently possible, as the v4l2_subdev_state_get_*() accessor functions take a non-const pointer to the state. Use _Generic() to provide two different versions of the accessors, for const and non-const states respectively. The former returns a const pointer to the requested format, rectangle or interval, implementing const-correctness. The latter returns a non-const pointer, preserving the current behaviour for drivers. Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> Reviewed-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx> --- Changes since v3: - Rename __v4l2_subdev_state_constify_call() to __v4l2_subdev_state_constify_ret() - Update documentation Changes since v2: - Specify types explicitly in _Generic() expression - Fix cast of value to const pointer Changes since v1: - Wrap the accessors with _Generic() using a single macro instead of adding a _Generic() statement in each of them. --- include/media/v4l2-subdev.h | 48 +++++++++++++++++++++++++------------ 1 file changed, 33 insertions(+), 15 deletions(-) diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h index b25b6e97ecbd..e1a6c49a966d 100644 --- a/include/media/v4l2-subdev.h +++ b/include/media/v4l2-subdev.h @@ -1326,6 +1326,16 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd); #define __v4l2_subdev_state_gen_call(NAME, _1, ARG, ...) \ __v4l2_subdev_state_get_ ## NAME ## ARG +/* + * A macro to constify the return value of the state accessors when the state + * parameter is const. + */ +#define __v4l2_subdev_state_constify_ret(state, value) \ + _Generic(state, \ + const struct v4l2_subdev_state *: (const typeof(*(value)) *)(value), \ + struct v4l2_subdev_state *: (value) \ + ) + /** * v4l2_subdev_state_get_format() - Get pointer to a stream format * @state: subdevice state @@ -1343,13 +1353,18 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd); * two or three arguments. The purpose of the __v4l2_subdev_state_gen_call() * macro below is to come up with the name of the function or macro to call, * using the last two arguments (_stream and _pad). The selected function or - * macro is then called using the arguments specified by the caller. A similar - * arrangement is used for v4l2_subdev_state_crop(), v4l2_subdev_state_compose() - * and v4l2_subdev_state_get_interval() below. + * macro is then called using the arguments specified by the caller. The + * __v4l2_subdev_state_constify_ret() macro constifies the returned pointer + * when the state is const, allowing the state accessors to guarantee + * const-correctness in all cases. + * + * A similar arrangement is used for v4l2_subdev_state_crop(), + * v4l2_subdev_state_compose() and v4l2_subdev_state_get_interval() below. */ -#define v4l2_subdev_state_get_format(state, pad, ...) \ - __v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad) \ - (state, pad, ##__VA_ARGS__) +#define v4l2_subdev_state_get_format(state, pad, ...) \ + __v4l2_subdev_state_constify_ret(state, \ + __v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad) \ + ((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__)) #define __v4l2_subdev_state_get_format_pad(state, pad) \ __v4l2_subdev_state_get_format(state, pad, 0) struct v4l2_mbus_framefmt * @@ -1368,9 +1383,10 @@ __v4l2_subdev_state_get_format(struct v4l2_subdev_state *state, * For stream-unaware drivers the crop rectangle for the corresponding pad is * returned. If the pad does not exist, NULL is returned. */ -#define v4l2_subdev_state_get_crop(state, pad, ...) \ - __v4l2_subdev_state_gen_call(crop, ##__VA_ARGS__, , _pad) \ - (state, pad, ##__VA_ARGS__) +#define v4l2_subdev_state_get_crop(state, pad, ...) \ + __v4l2_subdev_state_constify_ret(state, \ + __v4l2_subdev_state_gen_call(crop, ##__VA_ARGS__, , _pad) \ + ((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__)) #define __v4l2_subdev_state_get_crop_pad(state, pad) \ __v4l2_subdev_state_get_crop(state, pad, 0) struct v4l2_rect * @@ -1389,9 +1405,10 @@ __v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad, * For stream-unaware drivers the compose rectangle for the corresponding pad is * returned. If the pad does not exist, NULL is returned. */ -#define v4l2_subdev_state_get_compose(state, pad, ...) \ - __v4l2_subdev_state_gen_call(compose, ##__VA_ARGS__, , _pad) \ - (state, pad, ##__VA_ARGS__) +#define v4l2_subdev_state_get_compose(state, pad, ...) \ + __v4l2_subdev_state_constify_ret(state, \ + __v4l2_subdev_state_gen_call(compose, ##__VA_ARGS__, , _pad) \ + ((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__)) #define __v4l2_subdev_state_get_compose_pad(state, pad) \ __v4l2_subdev_state_get_compose(state, pad, 0) struct v4l2_rect * @@ -1410,9 +1427,10 @@ __v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state, * For stream-unaware drivers the frame interval for the corresponding pad is * returned. If the pad does not exist, NULL is returned. */ -#define v4l2_subdev_state_get_interval(state, pad, ...) \ - __v4l2_subdev_state_gen_call(interval, ##__VA_ARGS__, , _pad) \ - (state, pad, ##__VA_ARGS__) +#define v4l2_subdev_state_get_interval(state, pad, ...) \ + __v4l2_subdev_state_constify_ret(state, \ + __v4l2_subdev_state_gen_call(interval, ##__VA_ARGS__, , _pad) \ + ((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__)) #define __v4l2_subdev_state_get_interval_pad(state, pad) \ __v4l2_subdev_state_get_interval(state, pad, 0) struct v4l2_fract * -- Regards, Laurent Pinchart
