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

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Aug 13, 2019, at 3:59 AM, Sarah Newman <srn@xxxxxxxxx> wrote:
> 
> On 8/12/19 8:01 AM, Andrew Cooper wrote:
>> 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.
> 
> A potentially untrusted domain.

But wouldn’t that include both driver domains and stubdomains?

 -George

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