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

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jan,

On 08/08/2019 10:04, Jan Beulich wrote:
> On 08.08.2019 10:43, 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.
> What's fuzzy about Dom0 not being a guest (due to being a part of the
> host instead)?
Dom0 is not part of the host if you are using an hardware domain. I actually 
thought we renamed everything in Xen from Dom0 to hwdom to avoid the confusion.
I also would rather avoid to treat "dom0" as not a guest. In normal setup this 
is a more privilege guest, in other setup this may just be a normal guest (think 
about partitioning).
Cheers,

--
Julien Grall

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