[FFmpeg-devel] [PATCHv2] ffmpeg: modify tty state when stderr is redirected

[wm4]

On Mon, 12 Oct 2015 09:12:02 -0400
Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:

> On Mon, Oct 12, 2015 at 8:56 AM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Mon, 12 Oct 2015 08:39:53 -0400
> > Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
> >
> >> On Mon, Oct 12, 2015 at 8:24 AM, wm4 <nfxjfg at googlemail.com> wrote:
> >> > On Mon, 12 Oct 2015 08:14:14 -0400
> >> > Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
> >> >
> >> >> On Mon, Oct 12, 2015 at 8:03 AM, Michael Niedermayer
> >> >> <michael at niedermayer.cc> wrote:
> >> >> > On Mon, Oct 12, 2015 at 01:46:19PM +0200, Michael Niedermayer wrote:
> >> >> >> On Fri, Jul 31, 2015 at 01:48:18PM +0200, Nicolas George wrote:
> >> >> >> [...]
> >> >> >> >    -> "ttyctl -f" in ~/.zshrc, "bash_tty_mode=$(stty -g);
> >> >> >> >    PROMPT_COMMAND='stty $bash_tty_mode'" in ~/.bashrc; that can be added in
> >> >> >> >    the FAQ or the wiki.
> >> >> >>
> >> >> >>
> >> >> >> the patch was applied and this does not work
> >> >> >>
> >> >> >> the first segfault i see breaks the terminal
> >> >> >>
> >> >> >> a testcase is a script like:
> >> >> >> #!/bin/sh
> >> >> >> valgrind ./ffmpeg_g -i matrixbench_mpeg2.mpg -encryption_key 0123456789abcdef0011223344556677  -encryption_iv aabbccddeeff11335577999876542222  crypto:file-crypt.nut
> >> >> >>
> >> >> >> (with the aesni patches or anything else that causes a segfault)
> >> >> >>
> >> >> >> ls -alF /bin/sh
> >> >> >> lrwxrwxrwx 1 root root 4 Mar 29  2012 /bin/sh -> dash*
> >> >> >> (this is default on ubuntu)
> >> >> >
> >> >> > i think i got it working as long as bash is the users shell with
> >> >> > the suggested stty commands
> >> >>
> >> >> So it does not work with dash?
> >> >
> >> > dash isn't meant to be used interactively anyway?
> >>
> >> Good point, just now read up on this weird shell I have never heard
> >> of: https://en.wikipedia.org/wiki/Debian_Almquist_shell. However,
> >> Michael does bring up a point in that /bin/sh by default symlinks to
> >> dash on a rather large platform, namely Ubuntu. We need to find out a
> >> workaround for it.  I am of no use here; hopefully Michael finds
> >> something and posts.
> >>
> >> I will then collect them all and add to the wiki.
> >
> > No, for interactive shell, Debian and Ubuntu still use bash by default.
> > So even if /bin/sh is used to run a script, the /bin/sh itself will be
> > started from a bash. So I do not see the problem here.
> 
> There is still a problem (albeit a minor use case): suppose a user is
> running /bin/sh as his interactive shell. Maybe Michael for the sake
> of testing only POSIX compliant stuff prefers to work within a /bin/sh
> shell, and thus as soon as he opens his terminal (running bash as you
> said), he invokes a /bin/sh subshell on Debian or Ubuntu (other
> places, /bin/sh is usually a symlink to bash, with no issues).

What if a user runs "rm -rf /"? You can't care about _everything_,
nor should you - especially if the user decides to intentionally shoots
himself into the foot.

> In such a situation, the user is screwed: unfortunately, AFAIK, there
> is no way to do a "pre-prompt" command in /bin/sh, all one has is
> $PS1. Furthermore, I can't really ask Michael to change from /bin/sh
> symlinking to dash to a symlink to bash since he wants to test /bin/sh
> as implemented on a user's machine.