domU crashing with no root

[Rob Gardner <rob.gardner@hp.com>]

Has something in domU configuration changed recently... Lately I have 
not been able to get domU to boot successfully. My (condensed) config 
file looks like this:
kernel = "/boot/vmlinuz-2.6.12-xenU"
memory = 128
name = "Rob-VM%d" % vmid
cpu = -1   # leave to Xen to pick
vcpus = 1
nics=1
disk = [ 'file:/xen/disk-images/dom1.fs,sda1,w']
ip = add_offset_to_ip(get_current_ipaddr(),vmid)
netmask = get_current_ipmask()
gateway = get_current_ipgw()
hostname= "vm%d" % vmid
root = "/dev/sda1 ro"
extra = "4 VMID=%d" % vmid

And when I start the domain, I get the following boot messages:

IP-Config: Complete:
      device=eth0, addr=15.9.73.171, mask=255.255.248.0, gw=15.9.72.1,
     host=vm1, domain=, nis-domain=(none),
     bootserver=1.2.3.4, rootserver=1.2.3.4, rootpath=
Looking up port of RPC 100003/2 on 1.2.3.4
portmap: server 1.2.3.4 not responding, timed out
Root-NFS: Unable to get nfsd port number from server, using default
Looking up port of RPC 100005/1 on 1.2.3.4
portmap: server 1.2.3.4 not responding, timed out
Root-NFS: Unable to get mountd port number from server, using default
mount: server 1.2.3.4 not responding, timed out
Root-NFS: Server returned error -5 while mounting /tftpboot/vm1
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "sda1" or unknown-block(2,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on 
unknown-block(2,0)


I don't get it. This worked in the past. I want to boot from a loopback 
file, not an nfs server. Why does it think there is no sda1?

Thanks for any help.

Rob