Re: [FFmpeg-devel] [PATCH] avutil/opt: add AV_OPT_FLAG_FORCE_CONST

[Timo Rothenpieler <timo@rothenpieler.org>]

On 14.04.2024 22:30, Marton Balint wrote:
> 
> 
> On Sun, 14 Apr 2024, Timo Rothenpieler wrote:
> 
>> ---
>> doc/APIchanges      |  3 +++
>> libavutil/opt.c     | 14 ++++++++++++++
>> libavutil/opt.h     |  5 +++++
>> libavutil/version.h |  2 +-
>> 4 files changed, 23 insertions(+), 1 deletion(-)
> 
> Where do you intend to use this flag? So some justification or 
> description of your plans is missing from the commit message.

Some options in nvenc could be greatly simplified with it, where right 
now there's multiple if/switch-trees in the code, just to weed out 
invalid values.

Due to it technically being an API break, just turning it on for old 
options is not that easy, but it's something for a future major update.

>>
>> diff --git a/doc/APIchanges b/doc/APIchanges
>> index 63e7a47126..da2c87909b 100644
>> --- a/doc/APIchanges
>> +++ b/doc/APIchanges
>> @@ -2,6 +2,9 @@ The last version increases of all libraries were on 
>> 2024-03-07
>>
>> API changes, most recent first:
>>
>> +2024-04-xx - xxxxxxxxxx - lavu 59.15.101 - opt.h
>> +  Add AV_OPT_FLAG_FORCE_CONST.
>> +
>> 2024-04-11 - xxxxxxxxxx - lavc 61.5.102 - avcodec.h
>>   AVCodecContext.decoded_side_data may now be set by libavcodec after
>>   calling avcodec_open2().
>> diff --git a/libavutil/opt.c b/libavutil/opt.c
>> index d11e9d2ac5..9e51fa47f9 100644
>> --- a/libavutil/opt.c
>> +++ b/libavutil/opt.c
>> @@ -365,6 +365,20 @@ static int set_string_number(void *obj, void 
>> *target_obj, const AVOption *o, con
>>                 if (o_named->flags & AV_OPT_FLAG_DEPRECATED)
>>                     av_log(obj, AV_LOG_WARNING, "The \"%s\" option is 
>> deprecated: %s\n",
>>                            o_named->name, o_named->help);
>> +            } else if (o->flags & AV_OPT_FLAG_FORCE_CONST) {
>> +                av_log(obj, AV_LOG_ERROR, "The \"%s\" option only 
>> accepts one of its pre-defined constant values",
>> +                       o->name);
>> +                buf[0] = ':'; buf[1] = ' '; buf[2] = 0;
>> +                for (o_named = NULL; o_named = 
>> av_opt_next(target_obj, o_named); ) {
>> +                    if (o_named->type == AV_OPT_TYPE_CONST &&
>> +                        o_named->unit && o->unit &&
>> +                        !strcmp(o_named->unit, o->unit)) {
>> +                        av_log(obj, AV_LOG_ERROR, "%s%s", buf, 
>> o_named->name);
>> +                        buf[0] = ',';
>> +                    }
>> +                }
>> +                av_log(obj, AV_LOG_ERROR, "\n");
>> +                return AVERROR(EINVAL);
>>             } else {
>>                 if (o->unit) {
>>                     for (o_named = NULL; o_named = 
>> av_opt_next(target_obj, o_named); ) {
>> diff --git a/libavutil/opt.h b/libavutil/opt.h
>> index e6013662f6..67e2b687b2 100644
>> --- a/libavutil/opt.h
>> +++ b/libavutil/opt.h
>> @@ -305,6 +305,11 @@ enum AVOptionType{
>>  * Set if option constants can also reside in child objects.
>>  */
>> #define AV_OPT_FLAG_CHILD_CONSTS    (1 << 18)
>> +/**
>> + * The option will only accept AV_OPT_TYPE_CONST values.
>> + * Any other user supplied values will be rejected.
>> + */
> 
> What about built-in named constants, such as min/max/default?
> 
>> +#define AV_OPT_FLAG_FORCE_CONST     (1 << 19)
>>
>> /**
>>  * May be set as default_val for AV_OPT_TYPE_FLAG_ARRAY options.
>> diff --git a/libavutil/version.h b/libavutil/version.h
>> index 1f2bddc022..5de2d92146 100644
>> --- a/libavutil/version.h
>> +++ b/libavutil/version.h
>> @@ -80,7 +80,7 @@
>>
>> #define LIBAVUTIL_VERSION_MAJOR  59
>> #define LIBAVUTIL_VERSION_MINOR  15
>> -#define LIBAVUTIL_VERSION_MICRO 100
>> +#define LIBAVUTIL_VERSION_MICRO 101
>>
>> #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
>>                                                LIBAVUTIL_VERSION_MINOR, \
>> -- 
>> 2.34.1
> 
> Regards,
> Marton
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