Re: [Qemu-devel] [RFC 11/29] migration: new postcopy-pause state

[Peter Xu]

On Fri, Jul 28, 2017 at 10:53:00AM -0500, Eric Blake wrote:
> On 07/28/2017 03:06 AM, Peter Xu wrote:
> > Introducing a new state "postcopy-paused", which can be used to pause a
> > postcopy migration. It is targeted to support network failures during
> > postcopy migration. Now when network down for postcopy, the source side
> > will not fail the migration. Instead we convert the status into this new
> > paused state, and we will try to wait for a rescue in the future.
> > 
> > Signed-off-by: Peter Xu <address@hidden>
> > ---
> 
> You might want to use scripts/git.orderfile to put .json changes early
> in your diffs (interface before implementation makes for easier reviews).

Will do.

> 
> > +++ b/qapi-schema.json
> > @@ -667,6 +667,8 @@
> >  #
> >  # @postcopy-active: like active, but now in postcopy mode. (since 2.5)
> >  #
> > +# @postcopy-paused: during postcopy but paused. (since 2.10)
> > +#
> 
> You've missed 2.10; this should be 2.11.

Definitely. It should be for 2.11.

> Can this state occur without
> any explicit request (ie. old clients may be confused by it), or do you
> have to opt-in to a specific migration parameter to inform qemu that you
> are aware of how to handle this state?

Yes, it can occur automatically, without any operation from user's
side. And it does not have a tunable to switch it on/off - it'll
always be on (that's my plan, though), since IMHO holding at a paused
state is always better than crashing the source directly (that's what
we do now - when postcopy encountered network failure, the VM will
crash and data will be lost).

Thanks,

-- 
Peter Xu