[FFmpeg-devel] [PATCH] hwcontext: Skip derivation checking for an existing device if options are set

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of Mark
> Thompson
> Sent: Tuesday, May 3, 2022 2:09 AM
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: [FFmpeg-devel] [PATCH] hwcontext: Skip derivation checking
> for an existing device if options are set
> 
> If options are set then the user definitely intends to create a new
> device, so we shouldn't attempt to return an existing one.
> ---
>   libavutil/hwcontext.c | 26 ++++++++++++++++----------
>   1 file changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/libavutil/hwcontext.c b/libavutil/hwcontext.c
> index ab9ad3703e..c4e01e0e78 100644
> --- a/libavutil/hwcontext.c
> +++ b/libavutil/hwcontext.c
> @@ -653,18 +653,24 @@ int
> av_hwdevice_ctx_create_derived_opts(AVBufferRef **dst_ref_ptr,
>       AVHWDeviceContext *dst_ctx, *tmp_ctx;
>       int ret = 0;
> 
> -    tmp_ref = src_ref;
> -    while (tmp_ref) {
> -        tmp_ctx = (AVHWDeviceContext*)tmp_ref->data;
> -        if (tmp_ctx->type == type) {
> -            dst_ref = av_buffer_ref(tmp_ref);
> -            if (!dst_ref) {
> -                ret = AVERROR(ENOMEM);
> -                goto fail;
> +    // If we were derived (possibly transitively) from a device of
> the
> +    // target type then we want to return that original device,
> unless
> +    // options are set in which case we can skip this check because
> it
> +    // is definitely intended to create a new device.
> +    if (!options) {
> +        tmp_ref = src_ref;
> +        while (tmp_ref) {
> +            tmp_ctx = (AVHWDeviceContext*)tmp_ref->data;
> +            if (tmp_ctx->type == type) {
> +                dst_ref = av_buffer_ref(tmp_ref);
> +                if (!dst_ref) {
> +                    ret = AVERROR(ENOMEM);
> +                    goto fail;
> +                }
> +                goto done;
>               }
> -            goto done;
> +            tmp_ref = tmp_ctx->internal->source_device;
>           }
> -        tmp_ref = tmp_ctx->internal->source_device;
>       }
> 
>       dst_ref = av_hwdevice_ctx_alloc(type);
> --

This doesn't implement the matching of device parameters, which you 
were talking about:

You said that when deriving a device, an existing device should
only be returned when the parameters are the same.

This patch is doing something quite different.

Regards,
softworkz