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(a)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)?
TIA,
-d