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

[Lars Kurth <lars.kurth@xxxxxxxxxx>]

On 13/08/2019, 09:43, "George Dunlap" <George.Dunlap@xxxxxxxxxx> wrote:

    
    
    > 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?
    
I think the definition you provided looks good and is also along the lines 
which how most people use it
Lars    
    

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