Comment 5 for bug 205450

My best guess is that it is a problem with the xen initrd (/boot/initrd.img-2.6.24-12-xen).

It seems to be only loading the fuse module and not the SCSI modules or any of the xen modules.

The following are loaded by xend:
blktap
blkbk
xenblk
netloop
netbk

Do any of these and possible also SCSI modules need to be explicitly in the initrd too?

I tried adding the following to /etc/initramfs-tools/modules and then running update-initramfs -u

sd_mod
scsi_mod
blktap
blkbk
xenblk
netloop
netbk

The following similar thing happens:

[ 0.215498] Freeing unused kernel memory: 216k freed
Loading, please wait...
Begin: Loading essential drivers... ...
[ 0.433778] SCSI subsystem initialized
[ 0.434788] Driver 'sd' needs updating - please use bus_type methods
[ 0.458819] register_blkdev: cannot get major 8 for sd
[ 0.458836] vbd vbd-2049: 19 xlvbd_add at /local/domain/0/backend/tap/3/2049
[ 0.459117] register_blkdev: cannot get major 8 for sd
[ 0.459128] vbd vbd-2050: 19 xlvbd_add at /local/domain/0/backend/tap/3/2050
[ 5.547967] XENBUS: Waiting for devices to initialise: 295s...290s...285s...280s...275s...270s...265s...260s...255s...250s...245s...240s...235s...230s...225s...220s...215s...210s...205s...200s...195s...190s...185s...180s...175s...170s...165s...160s...155s...150s...145s...140s...135s...130s...125s...120s...115s...110s...105s...100s...95s...90s...85s...80s...75s...70s...65s...60s...55s...50s...45s...40s...35s...30s...25s...20s...15s...10s...5s...0s...
[ 298.329595] XENBUS: Device not ready: device/vbd/2049
[ 298.329599] XENBUS: Device not ready: device/vbd/2050
[ 298.348441] fuse init (API version 7.9)
[ 298.373876] thermal: Unknown symbol acpi_processor_set_thermal_limit
Done.
Begin: Running /scripts/init-premount ...
Done.
Begin: Mounting root file system... ...
Begin: Running /scripts/local-top ...
Done.
Begin: Waiting for root file system... ...
Done.
 Check root= bootarg cat /proc/cmdline
 or missing modules, devices: cat /proc/modules ls /dev
ALERT! /dev/sda2 does not exist. Dropping to a shell!

BusyBox v1.1.3 (Debian 1:1.1.3-5ubuntu12) Built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) cat /proc/modules
fuse 56368 1 - Live 0xffffffff8808c000
netbk 111600 0 [permanent], Live 0xffffffff8806f000
netloop 8960 0 - Live 0xffffffff8806b000
xenblk 22496 0 - Live 0xffffffff88064000
blkbk 26936 0 [permanent], Live 0xffffffff8805c000
blktap 123908 0 [permanent], Live 0xffffffff8803c000
xenbus_be 5888 3 netbk,blkbk,blktap, Live 0xffffffff88039000
sd_mod 33280 0 - Live 0xffffffff8802f000
scsi_mod 179000 1 sd_mod, Live 0xffffffff88002000
(initramfs)

I also noticed that /var/log/xen/xen-hotplug.log has:
Nothing to flush.
xenstore-read: couldn't read path backend/vbd/1/2049/node
xenstore-read: couldn't read path backend/vbd/1/2050/node
Nothing to flush.
xenstore-read: couldn't read path /local/domain/2/vm
xenstore-read: couldn't read path /local/domain/2/vm
Nothing to flush.

I still think it might have to do with the initrd, but not sure what exactly. Building from source did work, but it would be better to be able to use the ubuntu packages.