[Libvir] Restarting of libvirt_qemud daemon

[Daniel Veillard]

On Fri, Mar 09, 2007 at 03:25:44AM +0000, 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.
> 
>  - We always try to re-create a bridge device at startup, even if it already
>    exists. Likewise we always try to add the IPtables rules & start dnsmasq.
>    We can easily detect if the bridge already exists. I think we can probably
>    double check iptables rulles too., The tricky one is figuring out whether
>    a dnsmasq instance is still running.
> 
> Dealing with theses not only helps planned restarts, but will also make it
> possible start up the daemon again after a crash without having to kill off
> all guests & networks manually. So I think it is worth investigating what
> we can do to enable restarts. It might be worth waiting until we sort out
> whether we'll merge libvirt_qemud with the generic libvirtd remote daemon
> though so we don't have to do the work twice over.

  In general I really prefer restartable daemons especially if the client can
auto restart them if they are gone missing, it makes users and sysadmins
life so much easier (and avoid the need to start the daemon at bootup, which
is yet another pain), though I understand this may be hard to achieve because
we have too much state.
  With respect to the unification of the various daemons, this also sounds
like a really nice thing to have, but I must admit I'm a bit lost, I don't
have really a clear picture of all the requirements (and probably won't until
we finalize at least a first version of the networking support).

Daniel

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