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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/08/2019 15:53, George Dunlap wrote:
> On 8/8/19 10:13 AM, 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. 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).
> A literal guest is someone who doesn't live in the building (or work in
> the buliding, if you're in a hotel).  The fact that the staff cleaning
> rooms are restricted in their privileges doesn't make them guests of the
> hotel.
>
> The toolstack domain, the hardware domain, the driver domain, the
> xenstore domain, and so on are all part of the host system, designed to
> allow you to use Xen to do the thing you actually want to do: Run guests.
>
> And it's important that we have a word that distinguishes "domains that
> we only care about because they make it possible to run other domains",
> and "domains that we actually want to run".  "guest / host" is a natural
> terminology for these.
>
> We already have the word "domain", which includes dom0, driver domains,
> toolstack domains, hardware domains, as well as guest domains.  We don't
> need "guest" to be a synonym for "domain".

So...

Please can someone propose wording simple, clear wording for what
"guest" means.

~Andrew

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