[FFmpeg-devel] [RFC 2/6] Add common V4L2 request API code

[James Almer]

On 4/8/2019 5:12 PM, Jonas Karlman wrote:
> Signed-off-by: Jonas Karlman <jonas at kwiboo.se>
> ---
>  configure                 |   8 +
>  libavcodec/Makefile       |   1 +
>  libavcodec/hwaccel.h      |   2 +
>  libavcodec/v4l2_request.c | 885 ++++++++++++++++++++++++++++++++++++++
>  libavcodec/v4l2_request.h |  65 +++
>  5 files changed, 961 insertions(+)
>  create mode 100644 libavcodec/v4l2_request.c
>  create mode 100644 libavcodec/v4l2_request.h

> +int ff_v4l2_request_uninit(AVCodecContext *avctx)
> +{
> +    V4L2RequestContext *ctx = avctx->internal->hwaccel_priv_data;
> +    int ret;
> +
> +    av_log(avctx, AV_LOG_DEBUG, "%s: avctx=%p ctx=%p\n", __func__, avctx, ctx);
> +
> +    if (ctx->video_fd >= 0) {
> +        ret = ioctl(ctx->video_fd, VIDIOC_STREAMOFF, &ctx->output_type);
> +        if (ret < 0)
> +            av_log(avctx, AV_LOG_ERROR, "%s: output stream off failed, %s (%d)\n", __func__, strerror(errno), errno);
> +
> +        ret = ioctl(ctx->video_fd, VIDIOC_STREAMOFF, &ctx->format.type);
> +        if (ret < 0)
> +            av_log(avctx, AV_LOG_ERROR, "%s: capture stream off failed, %s (%d)\n", __func__, strerror(errno), errno);
> +    }
> +
> +    if (avctx->hw_frames_ctx) {
> +        AVHWFramesContext *hwfc = (AVHWFramesContext*)avctx->hw_frames_ctx->data;
> +        av_buffer_pool_reclaim(hwfc->pool);

What's the idea behind this? Calling this function will free all the
unused buffers currently residing in the pool, but will do nothing with
those already in assigned to some AVBufferRef created with
av_buffer_pool_get(). Those will in fact go back to the pool once they
are not needed anymore.

Other than immediately freeing up some memory, the new function you
added is not going to do much. It wont be until av_buffer_pool_uninit()
is called and all the assigned buffers if any returned to the pool that
everything will be effectively freed.