Device 769 (vbd) could not be connected

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

I try to boot a Linux domU. I use the install/boot/vmlinuz-2.6.18-xen
kernel from xen-3.1.0-install-x86_32.tgz

Here is the xen config file for the domU:

kernel = "/xen/kern/vmlinuz-2.6.18-xen"
memory = 1024
name = "boulet"
disk = [ 'file:/xen/vnd/boulet-hda1.vnd,hda1,w' ]
root = "/dev/hda1"
on_poweroff = 'destroy'
on_reboot   = 'restart'
on_crash    = 'restart'

And here is the result:
# xm create -c boulet
Using config file "./boulet".
# Error: Device 769 (vbd) could not be connected. Hotplug scripts not
working.

A web search tells me that this problem is known and can arise if the
disk image is sparse. It is not the case here:
# ls -sk /xen/vnd/boulet-hda1.vnd 
10243936 /xen/vnd/boulet-hda1.vnd
# du -k /xen/vnd/boulet-hda1.vnd  
10243936        /xen/vnd/boulet-hda1.vnd

If I comment out the disk line in the config file, the Linux kernel does
boot and panic at root mount time.

Any hint?
-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost