Re: [PATCH 3/5] migration: Notify migration FAILED before starting VM

[Fabiano Rosas <farosas@suse.de>]

Peter Xu <peterx@redhat.com> writes:

> On Fri, Jan 23, 2026 at 09:59:35AM -0300, Fabiano Rosas wrote:
>> Peter Xu <peterx@redhat.com> writes:
>> 
>> > Devices may opt-in migration FAILED notifiers to be invoked when migration
>> > fails.  Currently, the notifications happen in migration_cleanup().  It is
>> > normally fine, but maybe not ideal if there's dependency of the fallback
>> > v.s. VM starts.
>> >
>> > This patch moves the FAILED notification earlier, so that if the failure
>> > happened during switchover, it'll notify before VM restart.
>> >
>> 
>> The change to FAILED in patch 2 should come to this patch to avoid
>> having a window where the notification only happens at the end.
>
> Hmm.. Isn't that expected?  Even after patch 2, we still notify FAILED at
> the end for precopy.  It's the same for postcopy.
>

Sorry, I meant: s/at the end/after vm_start/.

> For a failed postcopy we have following behavior:
>
> Before patch 2
> ==============
>
>   - notify FAILED (during switchover)
>   - vm_start()
>   - notify FAILED (during migration_cleanup)
>
> After patch 2 
> =============
>
>   - vm_start()
>   - notify FAILED (during migration_cleanup)
>
> So patch 2 fixes the duplicate issue, and only fixes that.
>
> After patch 3
> =============
>
>   - notify FAILED (during migration_iteration_finish)
>   - vm_start()
>
> Patch 3 changes the place of FAILED notification so that it happens always
> before vm_start(), for both precopy and postcopy.

Right, my point is that with patch 3 we're establishing that the correct
place to notify is before vm_start(). But after patch 2, *if* any driver
actually depends on being informed of failure *before* starting the VM,
that will not happen. I think both changes could be made at once so that
this intermediate state never exists.