Re: [Xen-devel] Terminology for "guest" - Was: [PATCH] docs/sphinx: Introduction

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Aug 08, 2019 at 09:43:01AM +0100, Andrew Cooper wrote:
> On 08/08/2019 07:22, Jan Beulich wrote:
> > On 07.08.2019 21:41, Andrew Cooper wrote:
> >> --- /dev/null
> >> +++ b/docs/glossary.rst
> >> @@ -0,0 +1,37 @@
> >> +Glossary
> >> +========
> >> +
> >> +.. Terms should appear in alphabetical order
> >> +
> >> +.. glossary::
> >> +
> >> +   control domain
> >> +     A :term:`domain`, commonly dom0, with the permission and
> >> responsibility
> >> +     to create and manage other domains on the system.
> >> +
> >> +   domain
> >> +     A domain is Xen's unit of resource ownership, and generally has
> >> at the
> >> +     minimum some RAM and virtual CPUs.
> >> +
> >> +     The terms :term:`domain` and :term:`guest` are commonly used
> >> +     interchangeably, but they mean subtly different things.
> >> +
> >> +     A guest is a single virtual machine.
> >> +
> >> +     Consider the case of live migration where, for a period of
> >> time, one
> >> +     guest will be comprised of two domains, while it is in transit.
> >> +
> >> +   domid
> >> +     The numeric identifier of a running :term:`domain`.  It is
> >> unique to a
> >> +     single instance of Xen, used as the identifier in various APIs,
> >> and is
> >> +     typically allocated sequentially from 0.
> >> +
> >> +   guest
> >> +     See :term:`domain`
> >
> > I think you want to mention the usual distinction here: Dom0 is,
> > while a domain, commonly not considered a guest.
> 
> To be honest, I had totally forgotten about that.  I guess now is the
> proper time to rehash it in public.
> 
> I don't think the way it currently gets used has a clear or coherent set
> of rules, because I can't think of any to describe how it does get used.
> 
> Either there are a clear and coherent (and simple!) set of rules for
> what we mean by "guest", at which point they can live here in the
> glossary, or the fuzzy way it is current used should cease.

I've always referred to dom0 as a privileged guest, but a guest
after all. I think this is one of the differences of Xen vs KVM or
other hosted hypervisors.

Roger.

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