Re: [Qemu-devel] [PATCH] migration/fd: abort migration if receive POLLHUP event

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Apr 25, 2018 at 07:29:05AM +0000, wangxin (U) wrote:
> 
> > -----Original Message-----
> > From: Peter Xu [mailto:peterx@redhat.com]
> > Sent: Wednesday, April 25, 2018 11:32 AM
> > To: Daniel P. Berrangé <berrange@redhat.com>
> > Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>; wangxin (U)
> > <wangxinxin.wang@huawei.com>; qemu-devel@nongnu.org;
> > quintela@redhat.com; Gonglei (Arei) <arei.gonglei@huawei.com>
> > Subject: Re: [PATCH] migration/fd: abort migration if receive POLLHUP event
> > 

> > Ah, wait.  I just noticed that Xin mentioned about the loop already -
> > it's an infinite loop of SIGHUP.  I suppose it means that we'll just
> > never go into fd_accept_incoming_migration() at all?
> 
> Yeah, that's what I want to fix.
> 
> > 
> > If so, I'm not sure whether we should just always watch on G_IO_HUP
> > (and possibly G_IO_ERR too) in qio_channel_create_watch():
> > 
> >   GSource *ret = klass->io_create_watch(ioc, condition | G_IO_HUP |
> > G_IO_ERR);
> > 
> > Otherwise I'm not sure the same loop will happen for other users of
> > qio_channel_add_watch().
> 
> In my scenario, it's clear the client quit immediately and we
> never got a POLLIN event, otherwise, 
> the watch should be unregistered when POLLIN event coming. 
> As Daniel said, normally G_IO_IN will be the first event, we
> need to find why POLLIN event never happened, I'll try it.

Yes, I have always been under the belief that you're guaranteed to get a
POLLIN event when the client closes the connection, in addition to the
POLLHUP event, but it sounds like that is not happening so I guess I'm
mistaken in that.

In this case, it should be sufficient to just add the G_IO_HUP|G_IO_ERR
events when creating the watch - probably no need to add extra code to
the fd_accept_incoming_migration() method.

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 :|