This section apply to Debian Etch, as well as a Ubuntu 7.10.
If after booting your vm, you realize that you forget to add a special block from domain0, it is still possible to add it when you vm are runnig.
If you read the man page of xen :
# man xm
you will see that you need to do that :
# xm block-attach our_domU_id phy:/dev/hda /dev/sda rw
to add the real block device :
from dom0 to a domU. But it doesn't work actually, and you will get this error :
Error: Invalid mode Usage: xm block-attach <Domain> <BackDev> <FrontDev> <Mode> Create a new virtual block device.
Strange, as the mode in the man page did say :
Actually, you have to specify an other mode, w instead of rw, and r instead of ro.
So, you have to type this :
# xm block-attach our_domU_id phy:/dev/hda /dev/sda w
and it will work.