xm block-attach with optional backend parameter

[Matthew Mallozzi <matt.mallozzi@oracle.com>]

Hey,
    I am trying to attach a disk image file stored in a domU as a block 
device to dom0, using the command
          xm block-attach 0 file:/root/mydisk.img /dev/xvda 1
where 1 is the domain ID of the particular domU that I want to act as 
the backend/driver domain.
    I get an error about "Hotplug scripts not working", and I've already 
posted to the xen-users list for advice on simply getting this to work, 
but I was hoping that someone here might be able to walk me through the 
execution path of a block-attach command, so that I can dive into the 
code and insert print statements everywhere?  I've been able to follow 
what functions are being called and all that through the xm Python code, 
but I get lost when it starts to communicate with xend.  Any help would 
be much appreciated!

Thanks,
Matt