qemu no-shutdown feature in libvirt

[Peter Krempa]

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.