Re: [PATCH V1 00/32] Live Update

[Paolo Bonzini]

On 30/07/20 21:09, Steven Sistare wrote:
>> please spell it out.  Also, how does the functionality compare to
>> xen-save-devices-state and xen-load-devices-state?
>
> qmp_xen_save_devices_state serializes device state to a file which is loaded 
> on the target for a live migration.  It performs some of the same actions
> as cprsave/cprload but does not support live update-in-place.

So it is a subset, can code be reused across both?  Also, live migration
across versions is supported, so can you describe the special
update-in-place support more precisely?  I am confused about the use
cases, which require (or try) to keep file descriptors across re-exec,
which are for kexec, and so on.

>>> cprsave and cprload support guests with vfio devices if the caller first
>>> suspends the guest by issuing guest-suspend-ram to the qemu guest agent.
>>> The guest drivers suspend methods flush outstanding requests and re-
>>> initialize the devices, and thus there is no device state to save and
>>> restore.
>> This probably should be allowed even for regular migration.  Can you
>> generalize the code as a separate series?
>
> Maybe.  I think that would be a distinct patch that ignores the vfio 
> migration blocker 
> if the state is suspended.  Plus a qemu agent call to do the suspend.  Needs 
> more
> thought.

The agent already supports suspend, so that should be relatively easy.
Only the code to add/remove the VFIO migration blocker from a VM state
change notifier, or something like that, would be needed.

Paolo