[Libvir] Restarting of libvirt_qemud daemon
Richard W.M. Jones
rjones at redhat.com
Fri Mar 9 14:02:55 UTC 2007
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
>>>> & networks, or to detect when they crash. For the former, we could
>>>> 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.
Emerging Technologies, Red Hat http://et.redhat.com/~rjones/
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and make dark of the things which are in their nature excessively
obvious and simple" (Francis Maseres FRS, mathematician, 1759)
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