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I don't believe zero is a valid evtchn#, is > >>>> it? > >>> > >>> gfn 0 might be valid, but I'm also pretty sure evtchn 0 is not valid. > >> > >> GFN 0 very much is valid. > >> > >> evtchn 0 OTOH is explicitly not valid.  From evtchn_init(): > >> > >>     evtchn_from_port(d, 0)->state = ECS_RESERVED; > >> > >> > >> However, the fields being 0 doesn't mean not available.  That's the > >> signal to saying "not connected yet", because that's what dom0 gets > >> before xenconsoled starts up. > > > > Someone asked me the same a while back, and IIRC we don't state > > anywhere in the public headers that event channel 0 is reserved, > > however that has always? been part of the implementation. > > > > If we intend this to be reliable, we should add a define to the public > > headers in order to signal that 0 will always be reserved. > > I agree a comment should have been there; it's not clear to me what > useful #define we could add. `EVTCHN_PORT_INVALID 0` or some such, but a comment would also be fine, the point is to be part of the public interface. Thanks, Roger.