Re: [Qemu-devel] [PATCH] qmp: handle stop/cont in INMIGRATE state

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 19 Oct 2012 05:27:29 -0400 (EDT)
Paolo Bonzini <pbonzini@redhat.com> wrote:

> > What happens is that a stop command while in INMIGRATE state will just
> > be ignored. Actually, any stops while in a state that pauses vCPUs
> > are ignored.
> > 
> > Also, I don't understand what you meant by "racy", care to elaborate?
> 
>     Case 1:                               Case 2:
>     user runs qemu -incoming -S           user runs qemu -incoming -S
>     source connects                       cont command received
>     cont command received                 source connects
>  
> In case 1, the VM is resumed at the end of migration, in case 2 it
> is not and an error is reported on QMP.  After this patch, it is always
> resumed.
> 
>     Case 1:                               Case 2:
>     user runs qemu -incoming              user runs qemu -incoming
>     source connects                       stop command received
>     stop command received                 source connects
>  
> In case 1, the VM runs for a blink of an eye and then stops.  In case
> 2 it just starts, with no error reported.
> 
> > > In addition, there's nothing that really prevents the user from
> > > typing the block device's passwords before incoming migration is
> > > done, so we may as well allow that.
> > 
> > Have you tried it? We seem to support that already.
> 
> With HMP yes, with QMP no.  You just get "An incoming migration is
> expected before this command can be executed" and no clue that disks
> are encrypted.

We could move the bdrv_iterate() calls before the RUN_STATE_INMIGRATE check
in qmp_cont(), but if this patch fixes all the cases you mention then let's
just apply it.