Re: [Qemu-devel] Re: [PATCH] Fix freezing bug in curses console

From: "Daniel P. Berrange" <berrange@redhat.com>
To: qemu-devel@nongnu.org
Cc: Matthew Bloch <matthew@bytemark.co.uk>, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] Re: [PATCH] Fix freezing bug in curses console
Date: Sun, 1 Mar 2009 11:36:35 +0000	[thread overview]
Message-ID: <20090301113635.GA10538@redhat.com> (raw)
In-Reply-To: <20090228212116.GL20640@shareable.org>

On Sat, Feb 28, 2009 at 09:21:16PM +0000, Jamie Lokier wrote:
> Anthony Liguori wrote:
> > >>It's racy with select().  A better fix would be to create a pipe and write
> > >>to that pipe in the SIGWINCH handler.  You should then register an io
> > >>    
> > >
> > >Maybe a bottom half would work?  The scheduling of a bh shouldn't
> > >constitute "real work".
> > 
> > I think it still suffers from the same race condition so today it 
> > wouldn't work.  You could fix the bottom half scheduling though so that 
> > you could safely schedule a bottom half from a signal handler (using 
> > roughly the same trick).
> 
> Fwiw, it's perfectly sensible to have a single pipe which is shared by
> all signal handlers, just used to say "check for work flags set".

And if you need the main loop to be able to distinguish signals coming
out of the pipe, then just write the signum into the pipe as a byte,
instead of a single dummy byte. Or even write the whole 'siginfo_t'
struct passed to the signal handler, and read it out in sizeof(siginfo_t)
sized chunks for processing. 

Daniel
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