Re: [Libvir] Restarting of libvirt_qemud daemon

Richard W.M. Jones wrote: >Daniel P. Berrange wrote: >>On Fri, Mar 09, 2007 at 10:47:18AM +0000, Richard W.M. Jones wrote: >>>Daniel P. Berrange wrote: >>>>Thinking about later RPM upgrades I think we need to think about >>>>whether it >>>>will be possible to restart the libvirt_qemud while guests & >>>>networks are >>>>running. There's a couple of issues: >>>> >>>>- We do waitpid() to cleanup qemu & dnsmasq processes when we stop >>>>domains >>>> & networks, or to detect when they crash. For the former, we could >>>>may >>>> they daemons to avoid waitpid() cleanup, but we'd still need >>>>waitpid to >>>> be able to detect shutdowns. There is also the issue of enumerating >>>> running instances. >>>Maybe I'm missing something big here, but how would libvirt_qemud >>>regain connections to the running qemu monitor ptys? >> >>That's one of the challenges to be addressed :-) Fortunately the monitor >>is set to be exposed via /dev/pty/XXX, so if the restarted client can >>find out the path to the PTY, then it can re-open it. Maybe we just need >>to record a state file somewhere containing a PID & PTY path. > >Is it possible to start qemu with something like: > > qemu -monitor pipe:/var/some/known/place/pipe.UUID > >and then just look in /var/some/known/place/ in order to find the >running instances? I should add a note that you can tell if the qemu at the other end of the pipe has died by opening the pipe and writing something, for example a NO-OP command. If you get EPIPE (or SIGPIPE if you weren't careful to disable the signal) you can delete the pipe device.