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

From: Jan Beulich <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Lars Kurth" <lars.kurth@citrix.com>,
	StefanoStabellini <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Julien Grall" <julien.grall@arm.com>,
	Xen-devel <xen-devel@lists.xenproject.org>,
	"Ian Jackson" <ian.jackson@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] Terminology for "guest" - Was: [PATCH] docs/sphinx: Introduction
Date: Thu, 8 Aug 2019 09:04:24 +0000	[thread overview]
Message-ID: <eba4a457-5be0-ee55-28b5-f25973c743fa@suse.com> (raw)
In-Reply-To: <2e3a40d8-14ec-9f84-6a43-d7389bdbebf8@citrix.com>

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)?

Jan
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