Re: [Qemu-devel] [PATCH v3 0/7] migration: pause-before-switchover

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> On Wed, Oct 18, 2017 at 06:40:06PM +0100, Dr. David Alan Gilbert (git) wrote:
> 
> [...]
> 
> > The precopy flow is:
> > active->pre-switchover->device->completed
> > 
> > The postcopy flow is:
> > active->pre-switchover->postcopy-active->completed
> 
> The naming is still slightly confusing to me:
> 
> (1) we have a capability called "pause-before-switchover", so it feels
>     like there is something called "switchover" and if we enable this
>     we'll pause before that point;
> 
> (2) we have a new status "pre-switchover", it feels like that's the
>     point before we are in "switchover" state;
> 
> (3) we don't really have a "switchover" state, but instead it's called
>     "device" which is exactly the "switchover" action.
> 
> Considering (1) and (2), I would prefer "device" state to be just
> "switchover"...

Yes I stuck to pause-before-device and device originally; but
what we're doing during the 'device' stage is mostly saving device
state; the actual switchover occurs at the end.  So hmm.

> Further, not sure we can unify the state transition as well (say, we
> add this switchover state even without cap "pause-before-switchover"
> set, although it does not make much sense itself). Then, we can also
> unify the precopy/postcopy state machine into one:
> 
> active->
>   [pre-switchover->]      (optional, decided by "pause-before-switchover")
>     switchover->
>       [postcopy-active->] (optional, decided by "postcopy-arm")
>         completed

I didn't want to change the state transition behaviour without the
capability set, since that could upset an existing libvirt that would
get confused by the new state.

Dave

> (Sorry I am discussing the naming again instead of reviewing real
>  stuff!)
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK