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RE: [Xen-devel] Question about VBD interface

To: "'Ian Pratt'" <Ian.Pratt@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] Question about VBD interface
From: "David Lie" <lie@xxxxxxxxxxxxxxxx>
Date: Wed, 3 Nov 2004 22:16:52 -0500
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> > I'm wondering how guest domains are provided access to disks.  I suppose
> > Domain 0 has direct access to the actual hardware devices, and other
> domains
> > simply see a virtualized block device.  However, when a guest domain
> wants to
> > make a request to the disk, how does it get that request to Domain 0 and
> how
> > does Domain 0 actually receive those requests?  There appears to be a
> virtual
> > block device driver in drivers/xen/blkfront & blkback.  Is this the
> driver
> > used by the guest Domains to access the virtualized devices?
> Yes. The blkback driver goes in dom0 (or any other suitably
> privileged domain) and is able to export any block device Linux
> knows about (e.g. physical partition, LVM volume, loopback file
> etc) to it's peer blkfront driver in the guest domain.

Thanks for the prompt reply.  

I'm a bit confused on this point then since the blkfront driver doesn't
appear to make any hypervisor calls to Xen.  If it doesn't do this, how does
it communicate requests to the blkback driver that's actually managing the
block device?



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