Re: [PATCH 0/5] iotests: make meson aware of individual I/O tests

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Mar 03, 2023 at 04:49:36PM +0100, Thomas Huth wrote:
> On 03/03/2023 14.06, Daniel P. Berrangé wrote:
> > On Fri, Mar 03, 2023 at 10:45:40AM +0000, Daniel P. Berrangé wrote:
> > > On Fri, Mar 03, 2023 at 09:30:39AM +0100, Thomas Huth wrote:
> > > > On 02/03/2023 19.46, Daniel P. Berrangé wrote:
> > > > 3) When I tried this last year, I had a weird problem that
> > > >     the terminal sometimes gets messed up ... I wasn't able
> > > >     to track it down back then - could you check by running
> > > >     "make check-block" many times (>10 times) to see whether
> > > >     it happens with your series or not?
> > > 
> > > I've just seen this - echo got disabled on my terminal.
> > 
> > The problem is that testrunner.py script doing
> > 
> > # We want to save current tty settings during test run,
> > # since an aborting qemu call may leave things screwed up.
> > @contextmanager
> > def savetty() -> Iterator[None]:
> >      isterm = sys.stdin.isatty()
> >      if isterm:
> >          fd = sys.stdin.fileno()
> >          attr = termios.tcgetattr(fd)
> > 
> >      try:
> >          yield
> >      finally:
> >          if isterm:
> >              termios.tcsetattr(fd, termios.TCSADRAIN, attr)
> > 
> > 
> > When invoking 'check' this wraps around execution of the entire
> > 'check' script. IOW it saves/restores the terminal once.
> > 
> > When we invoke 'check' in parallel it will save/restore the same
> > terminal for each invokation.
> > 
> > If the 'termios.tcgetattr' call runs at the same time as there is
> > a QEMU running which has put the terminal in raw mode, then when
> > 'check' exits it'll "restore" the terminal to raw mode.
> > 
> > IOW, this savetty() logic is fundamentally unsafe when invoking
> > 'check' in parallel.
> 
> Hmm, couldn't we e.g. also simply skip this termios stuff when running with
> "--tap" ?

It actually turns out to be way simpler. We merely need to set
stdin=subprocess.DEVNULL. There is no valid reason for the test
cases to be reading for stdin, as that would block execution.
By setting stdin==/dev/null, the isatty(0) checks will fail and
thus QEMU won't mess with termios, and thus we don't need any
save/restore dance either.


With regards,
Daniel
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