[Qemu-devel] Re: [RFC PATCH 0/5] Save state error handling (kill off no_migrate)

[Alex Williamson]

On Tue, 2010-10-05 at 15:49 -0500, Anthony Liguori wrote:
> On 10/05/2010 03:46 PM, Alex Williamson wrote:
> > On Tue, 2010-10-05 at 15:41 -0500, Anthony Liguori wrote:
> >    
> >> On 10/05/2010 03:35 PM, Alex Williamson wrote:
> >>      
> >>> I was thinking of making KVM VMs with assigned PCI devices
> >>> unsavable/unmigratable, but I wasn't thrilled with the
> >>> no_migrate solutions.  The more generic solutions seems to be
> >>> simply letting save handlers return an error if the device can't
> >>> be migrated.  This is also much more generic than a one-way
> >>> bit flip of the no_migrate flag.  For a vmsd based registration,
> >>> the pre_save() routine seems to be the right place to allow
> >>> devices to abort.  The series also carries the error back through
> >>> all the vmstate callers.  If this looks good, I'll give it some
> >>> more testing and submit as non-RFC.  Thanks,
> >>>
> >>>        
> >> Doesn't this mean that we don't fail the migration until after
> >> transferring all of the memory contents?
> >>      
> > That's the case with the current no_migrate implementation too, it
> > doesn't get called until qemu_savevm_state_complete().  Thanks,
> >    
> 
> Ouch, that's unfortunate but also should be easily fixable.
> 
> But making a save handler fail seems would make it impossible to get 
> instant failure semantics.

True.  Ok, so maybe we do still need a separate no migrate registration.
In any case, I think it's a good idea to allow the save routines to have
a failure path, but I'll work on a way to disable migration that's not
quite so coupled with the savevm entry (it seems silly for device
assignment to register a savevm only for the purpose of then registering
as non-migratable).  Thanks,

Alex