hi keir,

this small patch fixes the losetup -r flag when we specify 'w!' to the disk mode.

the mode from canonicalise_mode can be 'r' 'w' or '!'. ian's patch doesn't consider
the '!' case.

when I specify 'w!' to a disk mode, will results disk setup failure.
log in /var/log/xen/xen-hotplug.log:
[--snip--]
losetup: invalid option -- !
usage:
  losetup loop_device                                       # give info
  losetup -d loop_device                                    # delete
  losetup -f                                                # find unused
  losetup -a                                                # list all used
  losetup -r                                                # read-only loop
  losetup [-e encryption] [-o offset] [-r] {-f|loop_device} file # setup
xenstore-read: couldn't read path backend/vbd/1/768/node
[--snip--]

ian, please confirm.

this patch should apply to xen-unstable and xen-3.2-testing as well.

regards,

zhigang