[libvirt] [PATCH] qemu: Prevent disk corruption on domain shutdown

[Eric Blake]

On 09/13/2011 10:20 AM, Jiri Denemark wrote:
> Ever since we introduced fake reboot, we call qemuProcessKill as a
> reaction to SHUTDOWN event. Unfortunately, qemu doesn't guarantee it
> flushed all internal buffers before sending SHUTDOWN, in which case
> killing the process forcibly may result in (virtual) disk corruption.
>
> By sending SIGQUIT instead of SIGTERM followed by SIGKILL we tell qemu
> to flush all buffers and exit. Once qemu exits, we will see an EOF on
> monitor connection and tear down the domain. In case qemu ignores
> SIGQUIT or just hangs there, the process stays running but that's not
> any different from a possible hang anytime during the shutdown process
> so I think it's just fine.

This affects virDomainShutdown, virDomainReboot, and guest-initiated 
shutdown, but not virDomainDestroy, right?

> ---
>   src/qemu/qemu_process.c |   21 +++++++++++++++++++--
>   src/qemu/qemu_process.h |    1 +
>   2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index f8a8475..8a12e2a 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -445,12 +445,12 @@ qemuProcessHandleShutdown(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
>                               qemuProcessFakeReboot,
>                               vm)<  0) {
>               VIR_ERROR(_("Failed to create reboot thread, killing domain"));
> -            qemuProcessKill(vm);
> +            qemuProcessQuit(vm);

Is this hunk right?  If we're that bad off that we can't create a 
thread, killing might actually be better.

>               if (virDomainObjUnref(vm) == 0)
>                   vm = NULL;
>           }
>       } else {
> -        qemuProcessKill(vm);
> +        qemuProcessQuit(vm);

But this seems right to me, although I'd like some weigh-in from danpb 
before committing it.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org