Re: Restarting of libvirt_qemud daemon

"Richard W.M. Jones" <rjones@xxxxxxxxxx> · Fri, 09 Mar 2007 14:02:55 +0000

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.

Rich.

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