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

[Jan Beulich <JBeulich@xxxxxxxx>]

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.

> I actually thought we renamed everything in Xen from Dom0 to hwdom
> to avoid the confusion.

As to variable naming - mostly, I think.

Jan
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