Re: [Xen-devel] Guest knowledge of own domid [was: docs: initial documentation for xenstore paths]

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-08-16 at 15:52 +0100, Daniel De Graaf wrote:
> On 08/16/2012 10:36 AM, Ian Campbell wrote:
> > On Thu, 2012-08-16 at 15:33 +0100, Daniel De Graaf wrote:
> > 
> >>>> and if two domains are attempting to
> >>>>> set up communication such as V4V or vchan, they need to be able to tell
> >>>>> their peer what domain ID to use.
> >>>
> >>> That's trickier.
> >>>
> >>> I suppose they could rendezvous via /vm/$UUID? Although there has been
> >>> talk of removing that path in the future.
> >>
> >> The /vm/$UUID path isn't currently useful for this, since it doesn't 
> >> maintain
> >> domain IDs (just names) and doesn't contain writable sub-keys for a domain
> >> to use. I also don't think such a sub-key should be added; it makes more
> >> sense to keep all of a domain's modifiable keys under its home path.
> >>
> >> Perhaps this could be changed to another identifier-to-domid mapping, like
> >> the proposed addition of a location to map name to domid? 
> >>
> >> The toolstack would maintain something like:
> >>   /local/by-name/$name == domid
> >>   /local/by-uuid/$uuid == domid
> > 
> > This second one is a bit like the existing /vm/$uuid/domid.
> 
> That key isn't being populated by xl on my system, so I didn't know it 
> existed.

I could have sworn I'd seen it recently, but don't now. Maybe I had
started xend at some point.

> > I think I would go with:
> > 
> >   /local/by-name/$name == /local/domain/$domid
> >   /local/by-uuid/$uuid == /local/domain/$domid
> > 
> > though, So that you can just read it and use it without interpreting it.
> 
> In that case, you would need to parse the domid out of the string in order
> to use it in hypercalls (grant, event, v4v). The frontend/backend paths use
> a distinct frontend-id/backend-id key for the domain ID, but we are trying
> to avoid this since populating this key would mean the domain populating it
> needs to know its own domain ID.

Right, dang ;-)

> >>   /local/domain/$domid/name - same as existing
> >>   /local/domain/$domid/uuid - ? maybe unneeded, as it's available from Xen.
> > 
> > Is it available for other domains via xen, or just yourself?
> > 
> 
> Yourself and anyone who can call getdomaininfo (which is usually just dom0).
> This is actually the same as the xenstore permissions on keys such as
> /local/domain/$id/name. Changing these may need consideration, because on
> public hosting servers, you might not want to allow domains to be enumerated
> by name.

Sure.



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel