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

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Lars Kurth" <lars.kurth@citrix.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Julien Grall" <julien.grall@arm.com>,
	"Ian Jackson" <ian.jackson@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] Terminology for "guest" - Was: [PATCH] docs/sphinx: Introduction
Date: Thu, 8 Aug 2019 09:43:01 +0100	[thread overview]
Message-ID: <2e3a40d8-14ec-9f84-6a43-d7389bdbebf8@citrix.com> (raw)
In-Reply-To: <ad94d279-e53c-b1ae-c333-096944b217dd@suse.com>

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.

~Andrew

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