[FFmpeg-devel] [PATCH 1/2] avutil/buffer: add av_buffer_pool_buffer_get_opaque

[Marton Balint]

On Sat, 14 Dec 2019, James Almer wrote:

> On 12/7/2019 6:57 PM, Marton Balint wrote:
>> In order to access the original opaque parameter of a buffer in the buffer
>> pool. (The buffer pool implementation overrides the normal opaque parameter but
>> also saves it so it is accessible).
>> 
>> Signed-off-by: Marton Balint <cus at passwd.hu>
>> ---
>>  doc/APIchanges      |  3 +++
>>  libavutil/buffer.c  |  6 ++++++
>>  libavutil/buffer.h  | 13 +++++++++++++
>>  libavutil/version.h |  4 ++--
>>  4 files changed, 24 insertions(+), 2 deletions(-)
>> 
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index 401c65a753..5b8d801f06 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -15,6 +15,9 @@ libavutil:     2017-10-21
>>
>>  API changes, most recent first:
>> 
>> +2019-12-xx - xxxxxxxxxx - lavu 56.37.100 - buffer.h
>> +  Add av_buffer_pool_buffer_get_opaque().
>> +
>>  2019-11-17 - 1c23abc88f - lavu 56.36.100 - eval API
>>    Add av_expr_count_vars().
>> 
>> diff --git a/libavutil/buffer.c b/libavutil/buffer.c
>> index f0034b026a..ec00fb22ec 100644
>> --- a/libavutil/buffer.c
>> +++ b/libavutil/buffer.c
>> @@ -355,3 +355,9 @@ AVBufferRef *av_buffer_pool_get(AVBufferPool *pool)
>>
>>      return ret;
>>  }
>> +
>> +void *av_buffer_pool_buffer_get_opaque(AVBufferRef *ref)
>> +{
>> +    BufferPoolEntry *buf = ref->buffer->opaque;
>> +    return buf->opaque;
>
> I'm not sure if this is a good idea. It takes any AVBufferRef as input,
> so it will crash on pretty much every one not created by an AVBufferPool
> (unless it checks that buf is not NULL before dereferencing it), or
> return something unrelated otherwise.

It is documented below that the buffer has to be part of the pool, so I 
don't really see this as an issue.

An alternative approach might be to introduce
AVBufferRef *av_buffer_pool_get2(AVBufferPool *pool, void **opaque);
which returns the original opauqe value of the allocated buffer in 
addition to returning the buffer.

Do you prefer this? Or maybe something entirely different?

Thanks,
Marton

>
>> +}
>> diff --git a/libavutil/buffer.h b/libavutil/buffer.h
>> index 73b6bd0b14..e0f94314f4 100644
>> --- a/libavutil/buffer.h
>> +++ b/libavutil/buffer.h
>> @@ -284,6 +284,19 @@ void av_buffer_pool_uninit(AVBufferPool **pool);
>>   */
>>  AVBufferRef *av_buffer_pool_get(AVBufferPool *pool);
>> 
>> +/**
>> + * Query the original opaque parameter of an allocated buffer in the pool.
>> + *
>> + * @param ref a buffer reference to a buffer returned by av_buffer_pool_get.
>> + * @return the opaque parameter set by the buffer allocator function of the
>> + *         buffer pool.
>> + *
>> + * @note the opaque parameter of ref is used by the buffer pool implementation,
>> + * therefore you have to use this function to access the original opaque
>> + * parameter of an allocated buffer.
>> + */
>> +void *av_buffer_pool_buffer_get_opaque(AVBufferRef *ref);
>> +
>>  /**
>>   * @}
>>   */
>> diff --git a/libavutil/version.h b/libavutil/version.h
>> index e18163388d..4de0fa1fc3 100644
>> --- a/libavutil/version.h
>> +++ b/libavutil/version.h
>> @@ -79,8 +79,8 @@
>>   */
>>
>>  #define LIBAVUTIL_VERSION_MAJOR  56
>> -#define LIBAVUTIL_VERSION_MINOR  36
>> -#define LIBAVUTIL_VERSION_MICRO 101
>> +#define LIBAVUTIL_VERSION_MINOR  37
>> +#define LIBAVUTIL_VERSION_MICRO 100
>>
>>  #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
>>                                                 LIBAVUTIL_VERSION_MINOR, \
>> 
>
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