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

[Tim Deegan <tim@xxxxxxx>]

At 22:14 +0100 on 14 Jun (1339712061), Jean Guyader wrote:
> On 14 June 2012 16:35, Tim Deegan <tim@xxxxxxx> 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. 

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?

Cheers,

Tim.

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