Re: [Qemu-devel] [PATCH v5 20/45] Modify savevm handlers for postcopy

[Dr. David Alan Gilbert]

* David Gibson (address@hidden) wrote:
> On Fri, Mar 13, 2015 at 10:19:54AM +0000, Dr. David Alan Gilbert wrote:
> > * David Gibson (address@hidden) wrote:
> > > On Wed, Feb 25, 2015 at 04:51:43PM +0000, Dr. David Alan Gilbert (git) 
> > > wrote:
> > > > From: "Dr. David Alan Gilbert" <address@hidden>
> > > > 
> > > > Modify save_live_pending to return separate postcopiable and
> > > > non-postcopiable counts.
> > > > 
> > > > Add 'can_postcopy' to allow a device to state if it can postcopy
> > > 
> > > What's the purpose of the can_postcopy callback?  There are no callers
> > > in this patch - is it still necessary with the change to
> > > save_live_pending?
> > 
> > The patch 'qemu_savevm_state_complete: Postcopy changes' uses
> > it in qemu_savevm_state_postcopy_complete and qemu_savevm_state_complete
> > to decide which devices must be completed at that point.
> 
> Couldn't they check for non-zero postcopiable state from
> save_live_pending instead?

That would be a bit weird.

At the moment for each device we call the:
       save_live_setup method (from qemu_savevm_state_begin)

   0...multiple times we call:
       save_live_pending
       save_live_iterate

   and then we always call
       save_live_complete


To my mind we have to call save_live_complete for any device
that we've called save_live_setup on (maybe it allocated something
in _setup that it clears up in _complete).

save_live_pending could perfectly well return 0 remaining at the end of
the migrate for our device, and thus if we used that then we wouldn't
call save_live_complete.

Dave

> 
> -- 
> David Gibson                  | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au        | minimalist, thank you.  NOT _the_ 
> _other_
>                               | _way_ _around_!
> http://www.ozlabs.org/~dgibson


--
Dr. David Alan Gilbert / address@hidden / Manchester, UK