Xen users - Feb 2014 - Xen on ARM: booting Linux from a physical partition

Hi,

I want to boot a Linux system from a root filesystem installed on an SD
card partition using an Arndale board.  To do this, I have a domain
configuration file,

  kernel = "/linux-domU"
  memory = 128
  name = "guest"
  vcpus = 1
  disk = [ 'phy:/dev/mmcblk1p4,xvda,w' ]
  extra = "... root=/dev/xvda ..."

I set up the filesystem by writing an ext3 filesystem image to the
partition mentioned in the config using 'dd'.  When the guest kernel
boots, I see

  blkfront: xvda: barrier or flush: disabled; persistent
    grants: enabled; indirect descriptors: disabled;
  xvda: unknown partition table

and then

  List of all partitions:
  ca00          991232 xvda  driver: vbd
  No filesystem could mount root, tried:  ext3 ext4 vfat fuseblk
  Kernel panic - not syncing: VFS: Unable to mount root fs on
    unknown-block(202,0)

I tried the 'file:' scheme for the disk setting in the configuration
file, but that causes the system to try to start QEMU.

In general the partition table message I mentioned is not problematic as
long as the device in question is not treated as a partitioned disk; I'd
just like to mount /dev/xvda rather than treat it that way, and
historically I've never had problems doing that.  And for what it's
worth, if I provide a physical device with a partition table instead of
blk1p4, the behavior is the same.

What am I missing?

Thanks!

-- 
  Jonathan Daugherty
  Software Engineer
  Galois, Inc.