libvirt users - Sep 2013 - Re: Trouble using virStream with callbacks

On Thu, Sep 19, 2013 at 12:59:33PM -0400, Jonathan Lebon
wrote:
> > poll() will be listening for i/o on the libvirt socket as well as
> > stdin, so it'll see incoming I/O from the guest.
> 
> That's strange, that's not what I'm seeing when running it
step-by-step. I see
> poll() hanging regardless of guest events. There are indeed two fds in the
> array (stdin and the other one being the libvirt socket I suppose), but in
all
> cases, I never observed an event occurring on the libvirt socket. Am I
missing
> a call to something here?
> 
> Note that I'm using 1.0.5.5 (daemon and library). Could things have
changed
> recently?
We've had quite a few changes sinc that release, so its always possible,
but at the smae time 'virsh console' has been using this code along time
and no one has complained about the problem you describe.
> 
> > One relevant thing is that stdio is line buffered by default and you
> > aren't putting it into raw mode like virsh console does. This will
> > delay I/O on the stdio streams.
> 
> That's a good point. But since all the messages between host and guest
end
> in newlines, that shouldn't be an issue, right? Anyway, I can see the
lines
> from stdin making it to virStreamSend() upon the first <Enter>. And
from the
> other side, it's safe to assume socat sends the data after the first
<Enter>
> as well (since it works fine with socat to socat directly on the
socket/port).
As a test why not try hacking virsh console so that it connects to your
virtio serial port, instead of a console. If we assume 'virsh console'
is bug-free, that would let you identify whether the flaw is in your host
code, or the guest side.

Daniel
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> As a test why not try hacking virsh console so that it connects to your
> virtio serial port, instead of a console. If we assume 'virsh
console'
> is bug-free, that would let you identify whether the flaw is in your host
> code, or the guest side.
Thanks for the pointer. Doing a few trivial changes to virsh-console does
show that it works correctly and pointed out multiple errors in the
original code (not least of which using VIR_EVENT_* constants instead of
VIR_STREAM_EVENT_*).

I have one more question, are there any risks associated with abandoning
threads and just doing the virEventRunDefaultImpl() in a loop after setting
up all the callbacks? I'm trying to keep this as simple as possible.

Cheers,

Jonathan

On Thu, Sep 19, 2013 at 05:43:58PM -0400, Jonathan Lebon
wrote:
> > As a test why not try hacking virsh console so that it connects to
your
> > virtio serial port, instead of a console. If we assume 'virsh
console'
> > is bug-free, that would let you identify whether the flaw is in your
host
> > code, or the guest side.
> 
> Thanks for the pointer. Doing a few trivial changes to virsh-console does
> show that it works correctly and pointed out multiple errors in the
> original code (not least of which using VIR_EVENT_* constants instead of
> VIR_STREAM_EVENT_*).
> 
> I have one more question, are there any risks associated with abandoning
> threads and just doing the virEventRunDefaultImpl() in a loop after setting
> up all the callbacks? I'm trying to keep this as simple as possible.
It is perfectly fine to use a single thread for everything. The only
reason virsh console doesn't do that, is that events were retrofitted
to existing code which wasn't event loop friendly, so we had to use a
second thread. One day we might fix virsh to only use one thread....

Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|