Re: [RFC][PATCH 0/5] Add V4V to Xen

[Jean Guyader <jean.guyader@citrix.com>]

On 25/06 10:05, Tim Deegan wrote:
> At 22:14 +0100 on 14 Jun (1339712061), Jean Guyader wrote:
> > On 14 June 2012 16:35, Tim Deegan <tim@xen.org> wrote:
> > > At 16:10 +0100 on 14 Jun (1339690244), Jean Guyader wrote:
> > >> On 14/06 03:56, Tim Deegan wrote:
> > >> > At 11:55 +0100 on 14 Jun (1339674908), Jean Guyader wrote:
> > >> > > Are you talking about having different version of V4V driver running
> > >> > > in the same VM?
> > >> >
> > >> > Yes.
> > >> >
> > >> > > I don't think that is a problem they both interact with Xen via
> > >> > > hypercall directly so if they follow the v4v hypercall interface it's
> > >> > > all fine.
> > >> >
> > >> > AFAICS if they both try to register the same port then one of them will
> > >> > silently get its ring discarded.  And if they both try to communicate
> > >> > with the same remote port their entries on the pending lists will get
> > >> > merged (which is probably not too bad).  I think the possibility for
> > >> > confusion depends on how you use the service.  Still, it seems better
> > >> > than the xenstore case, anyway. :)
> > >> >
> > >>
> > >> Not silently, register_ring will return an error.
> > >
> > > Will it?  It looks to me like v4v_ring_add just clobbers the old MFN
> > > list.
> > >
> > 
> > Ha yes. It does that now but I think it should return an error
> > informing up the stack that a ring has already been registered.
> 
> Actually, I think it's deliberate, to allow a guest to re-register all
> its rings after a suspend/resume or migration, without having to worry
> about whether it was actually migrated into a new domain or not. 
> 

Yes your are right. The driver will still try to register but a correct error
code could tell it weather or not it has been done.


> That raises the question of how a v4v client ought to handle migration;
> doesn't it have to rely on other OS components to notify it that one has
> happened?
>

Migration will cause the connection to close and the event will propagated
up the stack.

Jean