boot existing linux installation as additional xen domain

There is a second suse installation on /dev/sdb6 which can be booted directly from hard disk.
Now this os-image should be booted in addition to the installation at /dev/sdb5 via xen.
Xen does not seem to be able to mount the root file system though stated in the xen configuration file:
disk = [ 'phy:sdb6,sdb6,w' ]
root = "/dev/sdb6"

# -*- mode: python; -*-
#============================================================================
# Python configuration setup for 'xm create'.
# This script sets the parameters used when a domain is created using 'xm create'.
# You use a separate script for each domain you want to create, or
# you can set the parameters for the domain on the xm command line.
#============================================================================

kernel = "/boot/vmlinuz-xen"
ramdisk = "/boot/initrd-xen"

# Or use domUloader instead of kernel/ramdisk to get kernel from domU FS
#bootloader = "/usr/lib/xen/boot/domUloader.py"
#bootentry = "sdb6:/boot/vmlinuz-xen,/boot/initrd-xen"

# The domain build function. Default is 'linux'.
builder='linux'

memory = 256
vcpus = 2
name = "weblinux"

vif = [ 'mac=00:16:3e:00:00:11, bridge=xenbr0' ]
#disk = [ 'phy:sdb,sdb,r', 'phy:sdb6,sdb6,w' ]
disk = [ 'phy:sdb6,sdb6,w' ]
root = "/dev/sdb6"

# Extra arguments to pass to the kernel.
extra = "3"

# boot on floppy (a), hard disk (c) or CD-ROM (d)
# the drive letters are allocated dynamically by Windows
boot='d'

sdl=1

> xm create oldinst
Using config file "./oldinst".
Started domain weblinux

> xm console weblinux
xen_mem: Initialising balloon driver.
PCI: System does not support PCI
PCI: System does not support PCI
AppArmor: AppArmor Filesystem Enabled
NET: Registered protocol family 2
IP route cache hash table entries: 4096 (order: 3, 32768 bytes)
TCP established hash table entries: 16384 (order: 6, 262144 bytes)
TCP bind hash table entries: 16384 (order: 6, 262144 bytes)
TCP: Hash tables configured (established 16384 bind 16384)
TCP reno registered
Unpacking initramfs... done
Freeing initrd memory: 11468k freed
audit: initializing netlink socket (disabled)
type=2000 audit(1228240187.066:1): initialized
VFS: Disk quotas dquot_6.5.1
Dquot-cache hash table entries: 512 (order 0, 4096 bytes)
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 254)
io scheduler noop registered
io scheduler anticipatory registered
io scheduler deadline registered
io scheduler cfq registered (default)
Non-volatile memory driver v1.2
Xen virtual console successfully installed as xvc0
Event-channel device installed.
PNP: No PS/2 controller found. Probing ports directly.
i8042.c: No controller found.
mice: PS/2 mouse device common for all mice
cpuidle: using governor ladder
NET: Registered protocol family 1
registered taskstats version 1
XENBUS: Device with no driver: device/vbd/2064
XENBUS: Device with no driver: device/vbd/2070
XENBUS: Device with no driver: device/vif/0
XENBUS: Device with no driver: device/console/0
Freeing unused kernel memory: 224k freed
Write protecting the kernel read-only data: 1564k
netfront: Initialising virtual ethernet driver.
xen-vbd: registered block device major 8
blkfront: sdb: barriers enabled
sdb: sdb1 sdb2 sdb3 < sdb5 sdb6 >
blkfront: sdb6: barriers enabled
sysfs: duplicate filename 'sdb6' can not be created
------------[ cut here ]------------
WARNING: at fs/sysfs/dir.c:424 sysfs_add_one+0x48/0xd3()
Modules linked in: xenblk(+) xennet
Pid: 7, comm: xenwatch Not tainted 2.6.25.18-0.2-xen #1

Call Trace:
[<ffffffff8020c4b4>] dump_trace+0xbd/0x36a
[<ffffffff8020c7a1>] show_trace+0x40/0x57
[<ffffffff8042b74c>] dump_stack+0x72/0x7b
[<ffffffff8022d313>] warn_on_slowpath+0x58/0x80
[<ffffffff802d687f>] sysfs_add_one+0x48/0xd3
[<ffffffff802d76b8>] sysfs_create_link+0xb4/0x110
[<ffffffff8037c4e3>] device_add+0x14b/0x4c1
[<ffffffff802d1450>] register_disk+0x6c/0x189
[<ffffffff80301b95>] add_disk+0x44/0x51
[<ffffffff8800e05c>] :xenblk:backend_changed+0x174/0x1f8
[<ffffffff80389534>] otherend_changed+0x8a/0x92
[<ffffffff80387e01>] xenwatch_handle_callback+0x1d/0x52
[<ffffffff80387f98>] xenwatch_thread+0x162/0x184
[<ffffffff80240a79>] kthread+0x49/0x76
[<ffffffff8020bf38>] child_rip+0xa/0x12
DWARF2 unwinder stuck at child_rip+0xa/0x12

Leftover inexact backtrace:

[<ffffffff80240a30>] ? kthread+0x0/0x76
[<ffffffff8020bf2e>] ? child_rip+0x0/0x12

---[ end trace 8e705c510fb793ec ]---
BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
IP: [<ffffffff802d6937>] sysfs_addrm_start+0x2d/0x95
PGD eec3067 PUD eea6067 PMD 0
Oops: 0000 [1] SMP
last sysfs file:
CPU 0
Modules linked in: xenblk(+) xennet
Pid: 7, comm: xenwatch Not tainted 2.6.25.18-0.2-xen #1
RIP: e030:[<ffffffff802d6937>] [<ffffffff802d6937>] sysfs_addrm_start+0x2d/0x95
RSP: e02b:ffff88000fce7b70 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000004e90fce7b90
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88000fc2d800
RBP: ffff88000fce7b80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88000fce7b90
R13: 00000000fffffff4 R14: 0000000000000000 R15: ffff88000fce7c00
FS: 00007f1e1ab9b6f0(0000) GS:ffffffff80600000(0000) knlGS:0000000000000000
CS: e033 DS: 0000 ES: 0000
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process xenwatch (pid: 7, threadinfo ffff88000fce6000, task ffff88000fce4200)
Stack: ffff88000fce7b90 ffff88000eeb63c0 ffff88000fce7be0 ffffffff802d6e8d
0000000000000000 0000000000000000 0000000000000000 0000000000000000
00ff880001805b18 ffff88000ef81030 00000000fffffffe ffff88000ef75958
Call Trace:
[<ffffffff802d6e8d>] create_dir+0x4d/0x93
[<ffffffff802d6f0b>] sysfs_create_dir+0x38/0x4f
[<ffffffff8030b1bb>] kobject_add_internal+0xc9/0x187
[<ffffffff8030b361>] kobject_add_varg+0x58/0x67
[<ffffffff8030b475>] kobject_add+0x89/0x8b
[<ffffffff802fdb03>] blk_register_queue+0x4b/0x90
[<ffffffff80301b9d>] add_disk+0x4c/0x51
[<ffffffff8800e05c>] :xenblk:backend_changed+0x174/0x1f8
[<ffffffff80389534>] otherend_changed+0x8a/0x92
[<ffffffff80387e01>] xenwatch_handle_callback+0x1d/0x52
[<ffffffff80387f98>] xenwatch_thread+0x162/0x184
[<ffffffff80240a79>] kthread+0x49/0x76
[<ffffffff8020bf38>] child_rip+0xa/0x12
DWARF2 unwinder stuck at child_rip+0xa/0x12

Leftover inexact backtrace:

[<ffffffff80240a30>] ? kthread+0x0/0x76
[<ffffffff8020bf2e>] ? child_rip+0x0/0x12


Code: c0 b9 08 00 00 00 48 89 e5 41 54 49 89 fc 53 48 89 f3 f3 ab 49 89 34 24 48 c7 c7 80 0f 5e 80 e8 ce 61 15 00 48 8b 3d a1 82 40 00 <48> 8b 73 38 48 89 d9 48 c7 c2 38 65 2d 80 e8 e7 68 fc ff 48 85
RIP [<ffffffff802d6937>] sysfs_addrm_start+0x2d/0x95
RSP <ffff88000fce7b70>
CR2: 0000000000000038
---[ end trace 8e705c510fb793ec ]---
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...
XENBUS: Device not ready: device/vbd/2070



> xm list
Name ID Mem VCPUs State Time(s)
Domain-0 0 1747 2 r----- 212.3
weblinux 2 256 2 -b---- 0.8
> xm destroy weblinux