Re: [FFmpeg-devel] [PATCH 4/6 v2] avutil/mastering_display_metadata: add a new allocator function that returns a size

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> av_mastering_display_metadata_alloc() is not useful in scenarios where you need to
> know the runtime size of AVMasteringDisplayMetadata.
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavutil/mastering_display_metadata.c | 13 +++++++++++++
>  libavutil/mastering_display_metadata.h |  9 +++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/libavutil/mastering_display_metadata.c b/libavutil/mastering_display_metadata.c
> index 6069347617..ea41f13f9d 100644
> --- a/libavutil/mastering_display_metadata.c
> +++ b/libavutil/mastering_display_metadata.c
> @@ -18,6 +18,7 @@
>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
>   */
>  
> +#include <stddef.h>
>  #include <stdint.h>
>  #include <string.h>
>  
> @@ -29,6 +30,18 @@ AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc(void)
>      return av_mallocz(sizeof(AVMasteringDisplayMetadata));
>  }
>  
> +AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc_size(size_t *size)
> +{
> +    AVMasteringDisplayMetadata *mastering = av_mallocz(sizeof(AVMasteringDisplayMetadata));
> +    if (!mastering)
> +        return NULL;
> +
> +    if (size)
> +        *size = sizeof(*mastering);
> +
> +    return mastering;
> +}
> +
>  AVMasteringDisplayMetadata *av_mastering_display_metadata_create_side_data(AVFrame *frame)
>  {
>      AVFrameSideData *side_data = av_frame_new_side_data(frame,
> diff --git a/libavutil/mastering_display_metadata.h b/libavutil/mastering_display_metadata.h
> index c23b07c3cd..52fcef9e37 100644
> --- a/libavutil/mastering_display_metadata.h
> +++ b/libavutil/mastering_display_metadata.h
> @@ -77,6 +77,15 @@ typedef struct AVMasteringDisplayMetadata {
>   */
>  AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc(void);
>  
> +/**
> + * Allocate an AVMasteringDisplayMetadata structure and set its fields to
> + * default values. The resulting struct can be freed using av_freep().
> + *
> + * @return An AVMasteringDisplayMetadata filled with default values or NULL
> + *         on failure.
> + */
> +AVMasteringDisplayMetadata *av_mastering_display_metadata_alloc_size(size_t *size);
> +
>  /**
>   * Allocate a complete AVMasteringDisplayMetadata and add it to the frame.
>   *

Instead of this we should have a generic allocator like
void *av_frame_side_data_allocate(enum AVFrameSideDataType, size_t
*size, size_t elem_count), with the latter being used for the allocators
that allocate arrays (like AVRegionOfInterest); it has to be set to zero
for the others. This will also avoid creating new
av_*_create_side_data() functions.

- Andreas

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