[Xen-devel] [PATCH] Extboot support for Xen

Anthony Liguori
Tue, 15 Jan 2008 20:02:24 -0000

This patch adds extboot to Xen.  It should be pretty harmless as the moment
because it''s never enabled.  extboot allows arbitrary block devices to
be used
to boot guests including SCSI and PV disks.  I''ve tested it with both
Windows
and Linux guests in QEMU.

The version of QEMU in Xen is a bit old so I couldn''t complete the
plumbing.
The main problem is that Xen provides no way of exposing SCSI disks
right now
and PV disks aren''t actually accessible within QEMU.  I''m
hoping someone
else
can pick that up though as I''m pretty overcommitted at the moment.  The
extboot infrastructure is there though so it''s just a matter of
initializing it
with the appropriate BlockDriverState.

Another thing to look at is the choice of physical address.  extboot
occupies
1.5k of memory but option roms have to fall on a 2k boundary.  I stole
2k from
the space used by etherboot.  That should be fine since etherboot and
extboot
should never be loaded at the same time.  Of course, someone with more
insight
into hvmloader may know of a better place.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>