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

[Julien Grall <julien.grall@arm.com>]

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).

Cheers,

-- 
Julien Grall

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