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Re: [Qemu-devel] [PATCH] catch signals

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] [PATCH] catch signals
Date: Tue, 5 Aug 2008 17:35:19 +0100
User-agent: Mutt/1.4.1i

On Tue, Aug 05, 2008 at 06:09:39PM +0200, Gerd Hoffmann wrote:
> +#ifndef _WIN32
> +static void termsig_handler(int signal)
> +{
> +    switch (signal) {
> +    case SIGSEGV:
> +    case SIGBUS:
> +        /* returning from signal handler most likely isn't going to work */
> +        fprintf(stderr, "qemu: got signal %d (%s), taking emergency exit\n",
> +                signal, strsignal(signal));
> +        exit(1);

Neither of these functions are on the POSIX  async-signal-safe list,
so their use from signal handlers is not a good idea.

'man 7 signal' will detail the safe functions that can be used from
signal handlers. http://kerneltrap.org/man/linux/man7/signal.7

> +        break;
> +    default:
> +        qemu_system_shutdown_request();

This is ok it merely sets a flag

> +        vm_start();  /* In case we're paused */

I've not checked all the functions this calls to see if they
are safe, but I have a feeling this won't be safe in general
because the vm_state_notify() will invoke a number of callbacks
whose content we can't predict.

I think rather than trying todo anything in the signal handler,
it is safest to just set a flag and have its state checked
and acted upon in the main loop.

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