[libvirt] [PATCH v2 1/1] qemu: hide details of fake reboot

Don Koch aardvark at krl.com
Tue Apr 7 17:31:50 UTC 2020

On Thu, 19 Dec 2019 13:50:19 +0300
Nikolay Shirokovskiy wrote:

> If we use fake reboot then domain goes thru running->shutdown->running
> state changes with shutdown state only for short period of time.  At
> least this is implementation details leaking into API. And also there is
> one real case when this is not convinient. I'm doing a backup with the
> help of temporary block snapshot (with the help of qemu's API which is
> used in the newly created libvirt's backup API). If guest is shutdowned
> I want to continue to backup so I don't kill the process and domain is
> in shutdown state. Later when backup is finished I want to destroy qemu
> process. So I check if it is in shutdowned state and destroy it if it
> is. Now if instead of shutdown domain got fake reboot then I can destroy
> process in the middle of fake reboot process.
> After shutdown event we also get stop event and now as domain state is
> running it will be transitioned to paused state and back to running
> later. Though this is not critical for the described case I guess it is
> better not to leak these details to user too. So let's leave domain in
> running state on stop event if fake reboot is in process.
> Reconnection code handles this patch without modification. It detects
> that qemu is not running due to shutdown and then calls qemuProcessShutdownOrReboot
> which reboots as fake reboot flag is set.
> Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy at virtuozzo.com>

Question regarding this change: in the on-line documentation for virDomainReboot(),
it states:

   Due to implementation limitations in some drivers (the qemu driver,
   for instance) it is not advised to migrate or save a guest that is
   rebooting as a result of this API. Migrating such a guest can lead to a
   plain shutdown on the destination.

Is this still the case? In any event, how does one know when the reboot has
finished (assuming the VM reacted to it)?


More information about the libvir-list mailing list