[Xen-devel] architecture for backend domains

[Diwaker Gupta <diwakergupta@xxxxxxxxx>]

Hi,

I'm going through all of the latest Xen 2.0 documentation, and I had a
couple of questions:

o it seems from the docs that its possible to assign io privileges and
administrative privileges to *any* domain (apart from dom0, which has
these privileges built in IIRC). is this correct?

o can there be multiple backend domains for a single physical device
(like a network interface)? if so, then there is a scheduling involved
at multiple levels -- first Xen will have to schedule backends across
the physdev, and then each backend will have to schedule across the
domains that use it as backend. Further, what mechanism does Xen use
to determine which backend to direct pkts to and from the backend
which client domain to forward them to?

o if there is just one backend, how exactly does access to the devices
take place? From the docs, I gather that each domain using the device
has 2 rings -- one for sends and one for receivs (very generally
speaking). Also, the docs say that the backend can directly map
buffers of the virtual domains in Xen to enable DMA to them. But at
other places in the docs, I got the impression that client domains
(and not just backends) have these descriptor rings as well. So
basically I'm asking if all communication happens through the backend,
or do client domains talk directly to Xen.

Sorry if I'm being obtuse, really appreciate clarifications :)
TIA
-- 
Diwaker Gupta
http://resolute.ucsd.edu/diwaker


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