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RE: [Xen-devel] Is driver domain a dom0 or domU

To: "pradeep singh rautela" <rautelap@xxxxxxxxx>, "xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Is driver domain a dom0 or domU
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Thu, 17 May 2007 12:40:39 +0200
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Thread-topic: [Xen-devel] Is driver domain a dom0 or domU

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> pradeep singh rautela
> Sent: 17 May 2007 10:29
> To: xen-devel
> Subject: [Xen-devel] Is driver domain a dom0 or domU
> The wiki link at
> http://wiki.xensource.com/xenwiki/DriverDomain?highlight=%28dr
> iver%29%7C%28domain%29
> says it is domU.
> I don't think so.
> driver domain is a priviliged dom0 domain with backend driver along
> with the actual hardware driver part for the device it serves.

A driver domain is ANY domain that has (direct) access to hardware. In
the common case, only Dom0 is a driver domain, but if you assign a PCI
device to another domain, that becomes a driver domain. 

Only Dom0 [1] is PRIVILEGED, in the sense that only Dom0 can create,
destroy and otherwise manage other domains. DomU is any domain that
isn't Dom0. 

[1] In the current implementation of Xen. There is no technical reason
why more domains couldn't be privileged. Just like you can have multiple
users in a Linux-system that are "root" users (just that there can
obviously only be one that is CALLED root, but you can have any number
of different users that have root privilege). In Xen, there is a macro
called "IS_PRIV" (from memory). It checks a variable within the domain
structure that says whether the domain is privileged or not. Currently,
this variable is only set in one place, and that is during Dom0
creation. But with a suitable interface to change this variable, any
other domain could technically be made into a "privileged domain" (it
still would of course not be Dom0, as there can only be ONE Dom0 - that
is the domain with ID number zero!). 

> Is my understanding correct?
> Thank you
> --psr
> -- 
> ---
> pradeep singh rautela
> "Genius is 1% inspiration, and 99% perspiration" - not me :)
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