Re: [PATCH] xenbus: Fix loopback event channel assuming domain 0

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Oct 13, 2011 at 10:24:34AM +0100, Ian Campbell wrote:
> > >>  but
> > >> the only Linux change required for the second case is the posted fix to the
> > >> loopback event channel.
> > > 
> > > Unless dom0 is also running Linux? In which case it has no way to talk
> > > to the xenstored in the second domain?
> > 
> > Correct; I am not addressing this problem as dom0 is not running Linux here.
> 
> Sure, my concern was that we don't paint ourselves into a corner wrt
> future moves in this direction. I think I'm now convinced that this
> isn't the case and that everything is fine (thanks!).
> 
> > The other patches you pointed to do address that possibility with the ioctl,
> > which seems a good solution if you want to also run Linux in dom0
> 
> Agreed, I think the ioctl path will fit into your
> "xenstored_local_init()" path just the same as it fits into the current
> code.
> 
> > > How does the xenstored running in the second domain get the necessary
> > > page/evtchn numbers to allow it to communicate with dom0?
> > 
> > In my setup, it doesn't ever communicate with dom0 as dom0 dies once it
> > has set up the boot domains. For a more general case, the page/evtchn
> > numbers could be passed in a normal introduce message if they are made
> > available outside dom0 (perhaps by command-line parameters or via another
> > mechanism like v4v).
> 
> That rings a bell -- I think Deigo had them on the xenstored domain
> command line.
> 
> > > I assume it is guaranteed that xen_start_info->store_evtchn == 0 (and
> > > presumably xen_start_info->store_mfn == 0) for the real dom0?
> > 
> > Yes; the start_info page is zeroed prior to filling it in for dom0, and
> > these fields are not filled in.
> 
> Great.
> 
> The representation of your changes which diff chose was not terribly
> helpful for seeing the trees in the woods but I applied it and reviewed
> the result and it looks ok to me.

Daniel,

Could you please repost these two patches with Ian's Reviewed-by and rebase
it on top of 3.1-rc9 please?