Re: qemu no-shutdown feature in libvirt

On Tue, Dec 01, 2020 at 05:09:26PM +0100, Jiri Denemark wrote: > On Tue, Dec 01, 2020 at 15:34:05 +0100, Peter Krempa wrote: > > On Mon, Nov 30, 2020 at 14:45:18 -0500, Luna Xu wrote: > > > Hi developers, > > > > Hi, > > > > [...] > > > > > When I start a VM with the qemu command I can specify the -no-shutdown > > > flag so that my qemu process doesn't quit even if I shutdown the VM > > > from the inside (issue shutdown or halt command inside VM). The VM is > > > shutdown but the qemu process is not killed so that the jobs I > > > submitted before for example backup (drive-backup) can continue to run > > > even after VM gets shutdown by the user, and I'm able to check the > > > status of the job through qmp commands (by communicating with the qemu > > > process). > > > > As I've noted in my reply on libvirt-users, we currently don't support > > this on the shutdown part of the VM lifecycle. > > > > On the startup part you can use VIR_DOMAIN_START_PAUSED for a VM which > > didn't yet excecute any guest instructions. > > > > > Is anyone aware of any project that is currently implementing this > > > functionality? Thanks for reading. > > > > I don't think that there's anybody working on it. > > > > If you are interested in implementing the feature the idea would be to > > add a 'pause' action for <on_poweroff>pause</on_poweroff> along with a > > new 'virDomainPausedReason' such as VIR_DOMAIN_PAUSED_POWEROFF and > > > implement the lifecycle transition from PAUSED -> RUNNING via > > qemuDomainResume, which would in this case have to issue a > > 'system-reset' qmp command and emit the appropriate events. > > This is weird, the domain was paused just before being shut down so > resuming it should logically just resume the paused process and finish > the shutdown. On the other hand, domain shutdown as a result of calling > resume is weird too. > > So how about just adding a check to qemuDomainResume to report an error > if you try to resume a domain which was paused for shutdown? Note we have a virDomainReset() API that does a full machine/cpu reset, so if we're in the puased state after shutdown, then a reset followed by a resume is a valid way to boot the guest OS fresh. This is in fact how we fake graceful reboots. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|