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

[Sarah Newman <srn@xxxxxxxxx>]

On 8/13/19 1:43 AM, George Dunlap wrote:
> > On Aug 13, 2019, at 3:59 AM, Sarah Newman <srn@xxxxxxxxx> wrote:
> >
> > On 8/12/19 8:01 AM, Andrew Cooper wrote:
> > > On 12/08/2019 15:53, George Dunlap wrote:
> > > > On 8/8/19 10:13 AM, Julien Grall wrote:
> > > > > 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).
> > > > A literal guest is someone who doesn't live in the building (or work in
> > > > the buliding, if you're in a hotel).  The fact that the staff cleaning
> > > > rooms are restricted in their privileges doesn't make them guests of the
> > > > hotel.
> > > >
> > > > The toolstack domain, the hardware domain, the driver domain, the
> > > > xenstore domain, and so on are all part of the host system, designed to
> > > > allow you to use Xen to do the thing you actually want to do: Run guests.
> > > >
> > > > And it's important that we have a word that distinguishes "domains that
> > > > we only care about because they make it possible to run other domains",
> > > > and "domains that we actually want to run".  "guest / host" is a natural
> > > > terminology for these.
> > > >
> > > > We already have the word "domain", which includes dom0, driver domains,
> > > > toolstack domains, hardware domains, as well as guest domains.  We don't
> > > > need "guest" to be a synonym for "domain".
> > > So...
> > > Please can someone propose wording simple, clear wording for what
> > > "guest" means.
> > A potentially untrusted domain.
> But wouldn’t that include both driver domains and stubdomains?
Then how about: a domain which does not provide Xen-related services.





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