Re: [Xen-devel] [PATCH 3/4] docs: Document xenstore paths for domain hotplug features

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> Sent: 06 November 2015 18:08
> To: Paul Durrant; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Keir (Xen.org); Ian Campbell; Tim (Xen.org); Ian Jackson; Jan Beulich
> Subject: Re: [Xen-devel] [PATCH 3/4] docs: Document xenstore paths for
> domain hotplug features
> 
> On 06/11/15 17:21, Paul Durrant wrote:
> > Without some indication from an HVM domain it is not possible for a
> > toolstack to know whether instantiation of a new vbd or vif should
> > result in a new PV device of the appropriate type being instantiated
> > in a guest. (In other words whether PV drivers are present and
> > functioning).
> >
> > This patch document two paths which vif and vbd frontend drivers can
> > use to advertise their ability to respond to new vif or vbd
> > instantiations.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
> > Cc: Keir Fraser <keir@xxxxxxx>
> > Cc: Tim Deegan <tim@xxxxxxx>
> > ---
> >  docs/misc/xenstore-paths.markdown | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/docs/misc/xenstore-paths.markdown b/docs/misc/xenstore-
> paths.markdown
> > index 7701632..9e98d6f 100644
> > --- a/docs/misc/xenstore-paths.markdown
> > +++ b/docs/misc/xenstore-paths.markdown
> > @@ -387,6 +387,18 @@ A domain writable path. Available for arbitrary
> domain use.
> >  A domain may write version information for PV driver $NAME using
> >  this path.
> >
> > +#### ~/feature/hotplug/vif = ("0"|"1") [w,HVM]
> > +
> > +An HVM domain can indicate to a toolstack that it is capable
> > +of responding to instantiation of a new vif by bringing online a
> > +new PV network device without the need for a reboot.
> > +
> > +#### ~/feature/hotplug/vbd = ("0"|"1") [w,HVM]
> > +
> > +An HVM domain can indicate to a toolstack that it is capable
> > +of responding to instantiation of a new vbd by bringing online a
> > +new PV block device without the need for a reboot.
> 
> These flags are not inherently restricted to HVM guests.  Therefore, I
> would avoid specifying them as such.  (It is quite possible for a PV
> guest not to be able to hotplug a vbd for example.)

I wasn't sure that was true. My belief was that all pure PV guests would have 
frontends handling hot attach. I'm happy to drop the HVM tag in v2 though.

  Paul

> 
> ~Andrew

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