[libvirt PATCH 2/2] tests: don't set G_DEBUG=fatal-warnings on macOS

[Daniel P. Berrangé]

On Mon, May 02, 2022 at 03:28:50PM +0200, Martin Kletzander wrote:
> On Fri, Apr 29, 2022 at 01:05:42AM -0700, Andrea Bolognani wrote:
> > On Thu, Apr 28, 2022 at 05:55:41PM +0100, Daniel P. Berrangé wrote:
> > > On Thu, Apr 28, 2022 at 08:33:46AM -0700, Andrea Bolognani wrote:
> > > > In other words, the current implementation of g_poll() on macOS
> > > > doesn't follow the contract defined by GLib itself. It seems to me
> > > > that this is a (fairly serious) bug in the library, no?
> > > 
> > > It is significant, but long standing. GLib actually had this behaviour
> > > forever on macOS, but it regressed when Meson was introduced, until
> > > the recent fix.
> > > 
> > > The question is whether efficiency trumps API semantics. Normally I'm
> > > heavily biased towards API semantics, but poll is a performance
> > > critical API, so it isn't so easy to declare we must workaround all
> > > the quirks.
> > > 
> > > I filed a bug to raise the subject for discussion though
> > > 
> > >   https://gitlab.gnome.org/GNOME/glib/-/issues/2644
> > 
> > That's an excellent bug report! Thanks for spending time on it, and
> > let's see where the upstream discussion leads :)
> > 
> 
> Just so I don't sway the potential discussion in the issue to the wrong
> way, I'll ask here.  Since BROKEN_POLL is used due to poll() on OS/X not
> behaving correctly with fds=NULL, nfds=0 [0], wouldn't it be possible to
> "fix" at least the internal calls to g_poll() which are done when
> running the main loop since they always have at least one FD (the
> eventfd used to signal the main loop [1])?  I know it would not fix the
> problem, but it would at least workaround the part that is used the
> most, I presume.

The comment is somewhat misleading - the nfds=0 case is not actually
the main problem they were fixing. The real killer issue is that
poll() doesn't work with block/char devices - ie any /dev/NNN FD.
This is what broke QEMU because it failed with TAP device FDs.

> 
> [0] https://gitlab.gnome.org/GNOME/glib/-/blob/main/glib/gpoll.c#L59

Dunno why the comment mentions nfds=0 because the the original
commit message describes the device node FDs scenario.


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|