[FFmpeg-devel] [PATCH][RFC] ffmpeg: remove access to private FILE struct members on Windows

[Michael Niedermayer]

On Tue, Aug 04, 2015 at 01:04:34PM -0400, Ronald S. Bultje wrote:
> Hi,
> 
> On Tue, Aug 4, 2015 at 12:42 PM, Hendrik Leppkes <h.leppkes at gmail.com>
> wrote:
> 
> > On Mon, Aug 3, 2015 at 9:54 PM, Hendrik Leppkes <h.leppkes at gmail.com>
> > wrote:
> > > On Mon, Aug 3, 2015 at 9:30 PM, Nicolas George <george at nsup.org> wrote:
> > >> Le sextidi 16 thermidor, an CCXXIII, Michael Niedermayer a écrit :
> > >>> i also found this comment in a patch in my inbox:
> > >>>
> > >>> +  /* When using Standard C input functions, also check if there
> > >>> +   is anything in the buffer. After a call to such functions,
> > >>> +   the input waiting in the pipe will be copied to the buffer,
> > >>> +   and the call to PeekNamedPipe can indicate no input available.
> > >>> +   Setting stdin to unbuffered was not enough, IIRC */
> > >>> +  if (stdin->_cnt > 0)
> > >>> +  {
> > >>> +    char ch;
> > >>> +    //Read it
> > >>> +    read(0, &ch, 1);
> > >>> +    return ch;
> > >>> +  }
> > >>>
> > >>> This seems to explain what the code was intended to do
> > >>
> > >> That was my guess.
> > >>
> > >> This is ugly, and should be removed anyways. It is not possible to mix
> > stdio
> > >> and low-level reading like that, period.
> > >>
> > >> Fortunately, ffmpeg.c only uses stdin at one single place, a few lines
> > below
> > >> the corresponding code:
> > >>
> > >>         }else
> > >>             if(scanf("%d", &debug)!=1)
> > >>                 fprintf(stderr,"error parsing debug value\n");
> > >>
> > >> It needs to be changed to read a line with the low-level function
> > >> (read_key()), exactly like 40 above for the 'c' case. I can not brew a
> > patch
> > >> right now, sorry.
> > >>
> > >> I suspect this would not work:
> > >>
> > >> printf 'd42\nC ... fontfile ...\n' | ffmpeg ...
> > >>
> > >> because the C will end up in the stdio buffer.
> > >>
> > >>
> > >
> > > Good catch. This command doesn't work with or without the hunk this
> > > patch removes however.
> > > A simpler command without drawtext would be:
> > >
> > > printf 'd0\n?' | ffmpeg -i ...
> > >
> > > If you see help output, it works. Using another command instead of d0
> > > works fine, like a C command followed by a \n?
> > > It also doesn't work on Linux, so thats a more fundamental problem.
> > >
> > > Since this fixes a build failure, unless we can find a use-case where
> > > this hunk actually does make a difference, I would still rather remove
> > > it.
> > > If it causes any regression in the future, which we didn't think of
> > > now, I'll be here to work on a fix.
> > >
> >
> > Any further thoughts on this?
> >
> > I would love start setting up a VS2015 FATE box etc, once compilation
> > actually works.
> 
> 
> I thought the conclusion was to apply it? I certainly support that.

+1

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

Observe your enemies, for they first find out your faults. -- Antisthenes
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