Jeremy,
     Until recently, the maximum number of xvd block devices you could attach to
a Xen domU was 16.  This limitation turned out to be problematic for some users,
so it was expanded to handle a much larger number of disks.  However, this
requires a couple of changes in the way that blkfront scans for disks.  This
functionality is already present in the Xen linux-2.6.18-xen.hg tree; the
attached patch adds this functionality to the mainline xen-blkfront
implementation.  I successfully tested it on a 2.6.25 tree.  I build tested it
on 2.6.27-rc3, but couldn't get that tree to boot due to some other bug.

Signed-off-by: Chris Lalancette <clalance@redhat.com>