[FFmpeg-devel] [PATCH 4/4] avformat/avio: Move internal AVIOContext field to the end

[James Almer]

On 8/4/2021 1:24 PM, Andreas Rheinhardt wrote:
> This gets them off the ABI altogether at the cost of breaking the ABI
> once more now.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
> Do this and the preceding patch need a version bump?

You're not removing anything that was "public", so IMO no.

Changes in offsets are ok since the latest AVPacket addition was a few 
days ago, so the ABI is not frozen yet (And at this rate wont be until 
we branch out a 5.0 release).

> 
>   libavformat/avio.h | 98 ++++++++++++++++++++++------------------------
>   1 file changed, 47 insertions(+), 51 deletions(-)
> 
> diff --git a/libavformat/avio.h b/libavformat/avio.h
> index 0b35409787..ebf43bfe15 100644
> --- a/libavformat/avio.h
> +++ b/libavformat/avio.h
> @@ -148,9 +148,9 @@ enum AVIODataMarkerType {
>   
>   /**
>    * Bytestream IO Context.
> - * New fields can be added to the end with minor version bumps.
> - * Removal, reordering and changes to existing fields require a major
> - * version bump.
> + * New public fields can be added with minor version bumps.
> + * Removal, reordering and changes to existing public fields require
> + * a major version bump.
>    * sizeof(AVIOContext) must not be used outside libav*.
>    *
>    * @note None of the function pointers in AVIOContext should be called
> @@ -237,12 +237,14 @@ typedef struct AVIOContext {
>       int64_t (*seek)(void *opaque, int64_t offset, int whence);
>       int64_t pos;            /**< position in the file of the current buffer */
>       int eof_reached;        /**< true if was unable to read due to error or eof */
> +    int error;              /**< contains the error code or 0 if no error happened */
>       int write_flag;         /**< true if open for writing */
>       int max_packet_size;
> +    int min_packet_size;    /**< Try to buffer at least this amount of data
> +                                 before flushing it. */
>       unsigned long checksum;
>       unsigned char *checksum_ptr;
>       unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);
> -    int error;              /**< contains the error code or 0 if no error happened */
>       /**
>        * Pause or resume playback for network streaming protocols - e.g. MMS.
>        */
> @@ -259,12 +261,6 @@ typedef struct AVIOContext {
>        */
>       int seekable;
>   
> -    /**
> -     * max filesize, used to limit allocations
> -     * This field is internal to libavformat and access from outside is not allowed.
> -     */
> -    int64_t maxsize;
> -
>       /**
>        * avio_read and avio_write should if possible be satisfied directly
>        * instead of going through a buffer, and avio_seek will always
> @@ -272,37 +268,6 @@ typedef struct AVIOContext {
>        */
>       int direct;
>   
> -    /**
> -     * Bytes read statistic
> -     * This field is internal to libavformat and access from outside is not allowed.
> -     */
> -    int64_t bytes_read;
> -
> -    /**
> -     * seek statistic
> -     * This field is internal to libavformat and access from outside is not allowed.
> -     */
> -    int seek_count;
> -
> -    /**
> -     * writeout statistic
> -     * This field is internal to libavformat and access from outside is not allowed.
> -     */
> -    int writeout_count;
> -
> -    /**
> -     * Original buffer size
> -     * used internally after probing and ensure seekback to reset the buffer size
> -     * This field is internal to libavformat and access from outside is not allowed.
> -     */
> -    int orig_buffer_size;
> -
> -    /**
> -     * Threshold to favor readahead over seek.
> -     * This is current internal only, do not use from outside.
> -     */
> -    int short_seek_threshold;
> -
>       /**
>        * ',' separated list of allowed protocols.
>        */
> @@ -325,30 +290,61 @@ typedef struct AVIOContext {
>        */
>       int ignore_boundary_point;
>   
> +    int64_t written;
> +
> +    /**
> +     * Maximum reached position before a backward seek in the write buffer,
> +     * used keeping track of already written data for a later flush.
> +     */
> +    unsigned char *buf_ptr_max;
> +
> +    /*****************************************************************
> +     * No fields below this line are part of the public API. They
> +     * may not be used outside of libavformat and can be changed and
> +     * removed at will.
> +     * New public fields should be added right above.
> +     *****************************************************************

Since we got rid of this kind of notice from AVStream not too long ago, 
wouldn't it be better if we prevent it from happening here too?
You could introduce a new AVIOInternal opaque struct and field here, 
much like we did with AVStreamInternal and AVFormatInternal to solve the 
same problem.

> +     */
> +    /**
> +     * A callback that is used instead of short_seek_threshold.
> +     * This is currently internal only, do not use from outside.
> +     */
> +    int (*short_seek_get)(void *opaque);
> +
>       /**
> -     * Internal, not meant to be used from outside of AVIOContext.
> +     * Threshold to favor readahead over seek.
> +     * This is currently internal only, do not use from outside.
>        */
> +    int short_seek_threshold;
> +
>       enum AVIODataMarkerType current_type;
>       int64_t last_time;
>   
>       /**
> -     * A callback that is used instead of short_seek_threshold.
> -     * This is current internal only, do not use from outside.
> +     * max filesize, used to limit allocations
>        */
> -    int (*short_seek_get)(void *opaque);
> +    int64_t maxsize;
>   
> -    int64_t written;
> +    /**
> +     * Bytes read statistic
> +     */
> +    int64_t bytes_read;
>   
>       /**
> -     * Maximum reached position before a backward seek in the write buffer,
> -     * used keeping track of already written data for a later flush.
> +     * seek statistic
>        */
> -    unsigned char *buf_ptr_max;
> +    int seek_count;
> +
> +    /**
> +     * writeout statistic
> +     */
> +    int writeout_count;
>   
>       /**
> -     * Try to buffer at least this amount of data before flushing it
> +     * Original buffer size
> +     * used after probing to ensure seekback and to reset the buffer size
>        */
> -    int min_packet_size;
> +    int orig_buffer_size;
>   } AVIOContext;
>   
>   /**
>