[FFmpeg-devel] [PATCH] ffmpeg: modify tty state when stderr is redirected

[Ganesh Ajjanagadde]

On Wed, Jul 29, 2015 at 3:27 PM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Wed, Jul 29, 2015 at 02:43:52PM -0400, Ganesh Ajjanagadde wrote:
>> On Mon, Jul 27, 2015 at 9:56 AM, Ganesh Ajjanagadde
>> <gajjanagadde at gmail.com> wrote:
>> > This fixes Ticket2964
>> >
>> > Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>> > ---
>> >  ffmpeg.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/ffmpeg.c b/ffmpeg.c
>> > index 751c7d3..98f812e 100644
>> > --- a/ffmpeg.c
>> > +++ b/ffmpeg.c
>> > @@ -372,7 +372,7 @@ void term_init(void)
>> >          struct termios tty;
>> >          int istty = 1;
>> >  #if HAVE_ISATTY
>> > -        istty = isatty(0) && isatty(2);
>> > +        istty = isatty(0);
>> >  #endif
>> >          if (istty && tcgetattr (0, &tty) == 0) {
>> >              oldtty = tty;
>>
>> ping
>
> i dont mind applying this but i dont remember why it was there
> so this might break somethig and someone might then have to revert

See the long discussion I had (with my initial patch series) for full details.
A short summary is as follows:
in order to accept "q" and other stuff, ffmpeg has to change the terminal mode.
Once terminal mode is changed, on event of "hard" signal like SIGSEGV,
it is not the responsibility of ffmpeg to clean up and restore the
terminal state
that now appears as messed up.
I had a patch to do this, but this requires registering signal handler
for such signals,
and others had valid objections since the core dump is no longer clean.
Thus, terminal restoration should be handled by the shell.
Fortunately, zsh has such functionality (thanks Nicolas for pointing
this out!) via "ttyctl -f"
to "freeze" terminal, i.e prevent any process from damaging the
terminal state on exit.
In bash it is harder to do this; AFAIK requires manual intervention.

Unless fate tests redirect 2(stderr) and do not redirect 0(stdin),
functionality is identical.
Even otherwise, by above argument, I think this is the right thing to do.

>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> I have often repented speaking, but never of holding my tongue.
> -- Xenocrates
>
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