pygrub/hvm boot with alternate script= for block devices

[James Dingwall <james-xen@dingwall.me.uk>]

Hi,

I am doing some experimentation with xen and Ceph and have a problem
booting my guest when my disk = [] uses an alternate block script.
Installation from a .iso was ok since the boot device was a file but 
now
trying to boot from the rbd neither the hvmbuilder or pygrub can start
as they treat the first value after target= as the /dev node to try and
use.

My disk parameter looks like:
disk = [ 'format=raw, script=block-rbd, vdev=xvda, access=w,
target=image=ubuntu-test' ]

In the pygrub log:
OSError: [Errno 2] No such file or directory: 'image=ubuntu-test'

and there is a similar error trying an HVM boot.

My block-rbd script parses the value passed after target= to
dynamically rbd map the image and then call the write_dev function from
block-common.sh to save the corresponding /dev name in xenstore.
According to the logging that I have in my block-rbd script this isn't
even called before pygrub is executed.

Is there a good reason that the block devices aren't connected before
pygrub is called so that it can then be invoked with the appropriate
/dev device that has been written in xenstore?

Thanks,
James