Re: [Xen-devel] xenstore documentation

[Rolf Neugebauer <rolf.neugebauer@xxxxxxxxx>]

On Tue, 2005-10-04 at 18:24, NAHieu wrote:
> On 10/4/05, Rolf Neugebauer <rolf.neugebauer@xxxxxxxxx> wrote:
> > On Tue, 2005-10-04 at 14:25, harry wrote:
> > > On Tue, 2005-10-04 at 21:55 +0900, NAHieu wrote:
> > > > On 10/4/05, harry <harry@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > > > > If you look at writeDetails in
> > > > > tools/python/xen/xend/server/DevController.py you'll see the
> > > > > transactions which cause the back and front ends to get probed.
> > > > >
> > > > > The transactions contain extra fields as provided by the derived class
> > > > > specific to the device type and are written into the store in the
> > > > > locations constructed in the frontendPath and backendPath functions in
> > > > > DevController.py.  These paths contain the device id string as 
> > > > > specified
> > > > > when you registered your xenbus drivers.
> > > > >
> > > >
> > > > Does that mean if I want to write a new split device, I must patch
> > > > xend to let it aware of the new type of device?
> > >
> > > Yes.  You have to add a new class in python/xen/xend/server (see
> > > blkif.py as an example) and then hook this class into xend in
> > > XendDomainInfo.py and xm/create.py to get the config parameters passed
> > > correctly.
> >
> > or no ;) depending on what you want to do. so for example if you only
> > ever have one backend in the system then you "could" store that under a
> > well known name in the store and the frontends can simply read that.
> > you'll also need a place for the BE to watch for FE updates in a similar
> > fashion.
> >
> 
> Rolf, I am really suprised here: how can BE watch for FE updates? BE
> and FE are in different domain, so they cannot access each other
> xenstore tree. (??)
> 
> So exactly what did you mean?

so, you BE could set up:
/foobar/backend/domid = 2
/foobar/frontends          <- watch on this

then FE looks up /foobar/backend/domid
setup its end of eventchannel + grant for shared page
then creates:
/foobar/frontends/<domid>/fe_port
/foobar/frontends/<domid>/grant_ref

BE watch fires, reads port and GR and finalises device channel set up

Seems to work for me.

Rolf


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