Re: [Qemu-devel] [PATCH] sigfd: use pthread_sigmask

[Andreas Färber]

Am 09.06.2011 um 14:36 schrieb Andreas Färber:

> Am 09.06.2011 um 00:55 schrieb Alexander Graf:
>
> > Qemu uses signalfd to figure out, if a signal occured without the  
> > need
> > to actually receive the signal. Instead, it can read from the fd to  
> > receive
> > its news.
> >
> > Now, we obviously don't always have signalfd around. Especially not  
> > on
> > non-Linux systems. So what we do there is that we create a new  
> > thread,
> > block that thread on all signals and simply call sigwait to wait  
> > for a
> > signal we're interested in to occur.
> >
> > This all sounds great, but what we're really doing is:
> >
> >   sigset_t all;
> >
> >   sigfillset(&all);
> >   sigprocmask(SIG_BLOCK, &all, NULL);
> >
> > which - on Darwin - blocks all signals on the current _process_,  
> > not only
> > on the current thread. To block signals on the thread, we can use
> > pthread_sigmask().
> >
> > This patch does that, assuming that my above analysis is correct,  
> > and thus
> > renders Qemu useable on Darwin again.
> >
> > Reported-by: Andreas Färber <address@hidden>
> > CC: Paolo Bonzini <address@hidden>
> > CC: Jan Kiszka <address@hidden>
> > CC: Anthony Liguori <address@hidden>
> > Signed-off-by: Alexander Graf <address@hidden>
>
> According to POSIX:2008, the use of sigprocmask() is only well- 
> defined for a single-threaded process.

And of course I forgot:

Acked-by: Andreas Färber <address@hidden>

> This patch fixed the default configuration (without --enable-io- 
> thread) for me.

> Thanks,
> Andreas
>
> > ---
> > compatfd.c |    2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/compatfd.c b/compatfd.c
> > index bd377c4..41586ce 100644
> > --- a/compatfd.c
> > +++ b/compatfd.c
> > @@ -29,7 +29,7 @@ static void *sigwait_compat(void *opaque)
> >    sigset_t all;
> >
> >    sigfillset(&all);
> > -    sigprocmask(SIG_BLOCK, &all, NULL);
> > +    pthread_sigmask(SIG_BLOCK, &all, NULL);
> >
> >    while (1) {
> >        int sig;
> > --
> > 1.7.1