Re: [Qemu-devel] [PATCH 2/2] qemu-ga: Add the guest-suspend command

[Luiz Capitulino <lcapitulino@redhat.com>]

On Mon, 16 Jan 2012 15:18:37 -0200
Luiz Capitulino <lcapitulino@redhat.com> wrote:

> On Mon, 16 Jan 2012 17:13:39 +0000
> "Daniel P. Berrange" <berrange@redhat.com> wrote:
> 
> > On Mon, Jan 16, 2012 at 03:08:53PM -0200, Luiz Capitulino wrote:
> > > On Fri, 13 Jan 2012 14:48:04 -0700
> > > Eric Blake <eblake@redhat.com> wrote:
> > > 
> > > > > +
> > > > > +        pid = fork();
> > > > > +        if (!pid) {
> > > > > +            char buf[32];
> > > > > +            FILE *sysfile;
> > > > > +            const char *arg;
> > > > > +            const char *pmutils_bin = "pm-is-supported";
> > > > > +
> > > > > +            if (strcmp(mode, "hibernate") == 0) {
> > > > 
> > > > Strangely enough, POSIX doesn't include strcmp() in its list of
> > > > async-signal-safe functions (which is what you should be restricting
> > > > yourself to, if qemu-ga is multi-threaded), but in practice, I think
> > > > that is a bug of omission in POSIX, and not something you have to change
> > > > in your code.
> > > 
> > > memset() ins't either... sigaction() either, which begins to get
> > > annoying.
> > > 
> > > For those familiar with glib: isn't it possible to confirm it's using
> > > threads and/or acquire a global mutex or something?

Misread, sigaction() is there. The ones that aren't are strcmp(), strstr()
and memset(). Interestingly, they are all "string functions".


> > 
> > The most that GLib says is
> > 
> >   "The GLib threading system used to be initialized with g_thread_init().
> >    This is no longer necessary. Since version 2.32, the GLib threading
> >    system is automatically initialized at the start of your program,
> >    and all thread-creation functions and synchronization primitives
> >    are available right away.
> > 
> >    Note that it is not safe to assume that your program has no threads
> >    even if you don't call g_thread_new() yourself. GLib and GIO can
> >    and will create threads for their own purposes in some cases, such
> >    as when using g_unix_signal_source_new() or when using GDBus. "
> > 
> > The latter paragraph is rather fuzzy, which is probably intentional.
> > So I think the only safe thing, in order to be future proof wrt later
> > GLib releases, is to just assume you have threads at all times.
> 
> Yeah, and we do use GIO in qemu-ga...
> 
> Thanks Daniel.
> 
> > 
> > 
> > Daniel
>