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

From: Rich Persaud <persaur@gmail.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: "Lars Kurth" <lars.kurth@citrix.com>,
	StefanoStabellini <sstabellini@kernel.org>,
	"Wei Liu" <wl@xen.org>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Christopher Clark" <christopher.w.clark@gmail.com>,
	"Daniel Smith" <dpsmith@apertussolutions.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 07:22:51 -0400	[thread overview]
Message-ID: <F650D65F-2397-4DEA-89B1-B8924A09D111@gmail.com> (raw)
In-Reply-To: <c2654c96-3236-70ae-70cb-581cfa193aff@suse.com>


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On Aug 8, 2019, at 06:49, Jan Beulich <JBeulich@suse.com> wrote:
> 
>> On 08.08.2019 11:13, 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.
> 
> It's still the control domain then, and hence still part of the host.

With disaggregation and dom0less (how might we describe that term in the intro?) for edge/embedded Xen systems, there could be a mode where the control domain has never had privilege over the domain that handles the physical TPM, or the provider of the virtual TPM:  

  https://lists.gt.net/xen/devel/557782

Rich

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