[FFmpeg-devel] [PATCH] Move error codes definitions from lavc to lavu

[Michael Niedermayer]

On Sun, Mar 07, 2010 at 03:32:00PM +0100, Stefano Sabatini wrote:
> On date Thursday 2009-07-30 01:27:54 +0200, Stefano Sabatini encoded:
> > On date Tuesday 2009-07-21 04:04:32 +0200, Michael Niedermayer encoded:
> > > On Tue, Jul 21, 2009 at 01:54:39AM +0200, Stefano Sabatini wrote:
> > > > On date Monday 2009-07-20 17:24:45 +0200, Michael Niedermayer encoded:
> > > > > On Sun, Jul 19, 2009 at 12:09:16PM +0200, Stefano Sabatini wrote:
> > > > > > Hi, as in subject,
> > > > > > 
> > > > > > this is required if we want for example move the error handling code
> > > > > > to lavu, as it uses it. Also reduces the clutter in avcodec.h.
> > > > > 
> > > > > i am fine with the move in priciple but didnt we want to deprecate the
> > > > > AVERROR_* macros in favor of AVERROR(E*) ?
> > > > 
> > > > What about AVERROR_PATCHWELCOME?
> > > 
> > > that has no E* so it can stay
> > 
> > Fine.
> >  
> > > > 
> > > > Also how AVERROR(XXX) is better than AVERRROR_XXX?
> > > 
> > > it needs less code
> > > 
> > > 
> > > > 
> > > > Also are we sure mapping A/V multimedia specific errors to POSIX
> > > > errors is a good idea?
> > > 
> > > Without an alternative suggestion its hard to say ...
> > 
> > My idea is to use AVERROR(EXXX) for each error which can be specified
> > using POSIX error codes, *then* having a minimal but meaningful list
> > of AVERROR_XXX FFmpeg error codes.
> > 
> > For example:
> > AVERROR_PATCHWELCOME
> > AVERROR_NO_OPTION_FOUND
> > AVERROR_UNSUPPORTED_FORMAT
> > AVERROR_VBV_FAILURE
> > 
> > and a corresponding av_errstring() func.
> > 
> > > > Also how can we say that e.g. -MKTAG('P','A','W','E') doesn't clutter
> > > > with a POSIX error code?
> > > 
> > > we cannot but it works with all systems for which ive seen E* values
> > > and a clash is exceedingly unlikely (1 in many millions) if a clash
> > > happens we just change it and bump major ver, given the low likeliness
> > > of conflict this seems acceptable to me but i guess some will disagree
> > 
> > Not very fine but acceptable (we may change idea in a distant? future).
> > 
> > > > Also the use of the POSIX error codes is arguable (ENOENT is used for
> > > > example when we don't find an option in a context, doxy is "No such
> > > > file or directory"), EILSEQ -> "unknown format", EDOM -> "Number
> > > > syntax expected in filename".
> > >
> > > > Also how can we map an error code to an error message?
> > > 
> > > by writing a function that does that
> > >
> > > 
> > > > 
> > > > All these questions raise the old problem of how to deal more sanely
> > > > with errors in libav*... and since I don't want to get stucked there,
> > > 
> > > what old problem exactly do you refer to here?
> > > which issue number on roundup is it?
> > 
> > No roundup issue, but the issue has been discussed sometimes in the
> > past (mainly proposed by Takis or me):
> > 
> > http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/54380
> > http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/68265/focus=78180
> 
> It seems we agree to choose when possible error codes borrowed from
> POSIX, otherwise use the -MKTAG trick for creating FFmpeg specific
> error codes.
> 
> This also means that we should drop all the AVERROR_* macros which
> have a corresponding code in POSIX.
> 
> Then we have to deal with the FFmpeg specific error codes. Actually
> we have just one of them (AVERROR_PATCHWELCOME).
> 
> Possible idea:
> 
> #define AVERROR2(a, b, c, d) -MKTAG(a, b, c, d)
> then we could use it like:
>         return AVERROR2('P','A','W','E');
> 

obfuscated


[...]
>  #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
> diff --git a/libavutil/common.h b/libavutil/common.h
> index 4b757d1..547b7d0 100644
> --- a/libavutil/common.h
> +++ b/libavutil/common.h
> @@ -35,6 +35,16 @@
>  #include <stdlib.h>
>  #include <string.h>
>  
> +/** Returns a negative error code from a POSIX error code, to return from library functions. */
> +#if EINVAL > 0
> +#define AVERROR(e) (-(e))
> +#else
> +/* Some platforms have E* and errno already negated. */
> +#define AVERROR(e) (e)
> +#endif
> +

> +#define AVERROR_PATCHWELCOME    -MKTAG('P','A','W','E') ///< Not yet implemented in FFmpeg. Patches welcome.

missig ()

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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