Re: [Qemu-devel] [PATCH] Use SIGIO with caution

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/29/2011 04:50 PM, Andreas Färber wrote:
> BeOS and Haiku don't define SIGIO. When undefined, it won't arrive
> and doesn't need to be blocked.
>
> Signed-off-by: Andreas Färber<andreas.faerber@web.de>

Anything to do with signal masks is never a trivial patch BTW...

But I actually think explicit handling of SIGIO is unneeded.  I think 
this is a hold over from the pre-I/O thread days where we selectively 
set SIGIO on certain file descriptors to make sure that when an IO fd 
became readable, we received a signal to break out of the KVM emulation 
loop.

Can the folks on CC confirm/deny?

I can't see any use of SIGIO in the current source tree.

Regards,

Anthony Liguori

> ---
>   cpus.c |    8 ++++++++
>   1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 1fc34b7..42af291 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -395,7 +395,9 @@ static int qemu_signal_init(void)
>       pthread_sigmask(SIG_UNBLOCK,&set, NULL);
>
>       sigemptyset(&set);
> +#ifdef SIGIO
>       sigaddset(&set, SIGIO);
> +#endif
>       sigaddset(&set, SIGALRM);
>       sigaddset(&set, SIG_IPI);
>       sigaddset(&set, SIGBUS);
> @@ -408,7 +410,9 @@ static int qemu_signal_init(void)
>            * We need to process timer signals synchronously to avoid a race
>            * between exit_request check and KVM vcpu entry.
>            */
> +#ifdef SIGIO
>           sigaddset(&set, SIGIO);
> +#endif
>           sigaddset(&set, SIGALRM);
>       }
>   #endif
> @@ -449,12 +453,16 @@ static void qemu_kvm_init_cpu_signals(CPUState *env)
>   #else
>       sigemptyset(&set);
>       sigaddset(&set, SIG_IPI);
> +#ifdef SIGIO
>       sigaddset(&set, SIGIO);
> +#endif
>       sigaddset(&set, SIGALRM);
>       pthread_sigmask(SIG_BLOCK,&set, NULL);
>
>       pthread_sigmask(SIG_BLOCK, NULL,&set);
> +#ifdef SIGIO
>       sigdelset(&set, SIGIO);
> +#endif
>       sigdelset(&set, SIGALRM);
>   #endif
>       sigdelset(&set, SIG_IPI);