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Re: [Xen-devel] Question about VBD interface

To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Question about VBD interface
From: "Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 4 Nov 2004 03:38:06 +0000
Cc: "David Lie" <lie@xxxxxxxxxxxxxxxx>, "'Ian Pratt'" <Ian.Pratt@xxxxxxxxxxxx>
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> 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?

The block frontend only makes hypercalls in order to send "events" to the 
backend driver when new requests are waiting in the shared memory region (the 
shared memory region is updated by just assigning to structs in a ring buffer 
and incrementing an integer index).

In the network frontend, hypercalls are also used to relinquish buffer pages 
to the backend driver but this is not necessary for block devices.


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