Re: [Qemu-devel] [PATCH v4 4/4] migration: Expose 'cancelling' status to user

[Dr. David Alan Gilbert]

* Eric Blake (address@hidden) wrote:
> On 03/13/2015 04:49 AM, Paolo Bonzini wrote:
> > 
> > 
> > On 09/03/2015 07:45, zhanghailiang wrote:
> >> 'cancelling' status was introduced by commit 51cf4c1a, mainly to avoid a 
> >> possible start of a new migration process while the previous one still 
> >> exists.
> >> But we didn't expose this status to user, instead we returned the 'active' 
> >> state.
> >>
> >> Here, we expose it to the user (such as libvirt), 'cancelling' status only
> >> occurs for a short window before the migration aborts, so for users,
> >> if they cancel a migration process, it will observe 'cancelling' status
> >> occasionally.
> >>
> >> Testing revealed that with older libvirt (anything 1.2.13 or less) will
> >> print an odd error message if the state is seen, but that the migration
> >> is still properly cancelled. Newer libvirt will be patched to recognize
> >> the new state without the odd error message.
> >>
> >> Signed-off-by: zhanghailiang <address@hidden>
> >> Reviewed-by: Eric Blake <address@hidden>
> >> Cc: address@hidden
> > 
> > Why is this necessary?
> 
> It simplifies qemu's job of reporting migration status information (qemu
> is no longer maintaining one set of states internally and a different
> set of states externally), and I already have the libvirt counterpart
> patch ready to go to gracefully accept the new state name.

Yes, it does make life simpler in the long run.
(It does worry me a bit what happens to new qemu on old libvirt)

Dave

> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 


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