[PATCH 00 of 29 RFC] libxl: move device plug/unplug to a separate daemon

[Roger Pau Monne <roger.pau@entel.upc.edu>]

This is the first attempt to delegate hotplug device plug/unplug to a 
separate daemon. This will also allow to plug/unplug devices from a 
domain different than Dom0, usually called a "driver domain".

This series contain a mix of bug fixes, mainly for device 
unplug/destroy synchronization, and a set of new functions that 
describe a new protocol to be used when delegating the plug/unplug of 
devices to a daemon, called xldeviced (xl-device-daemon).

As a very important note, I would like to add that this has only been 
tested with PV DomUs, and that qdisk support is missing (xldeviced is 
not prepared to launch a qemu-dm to support qdisk devices). I will 
work on that, but I think there's already a lot of stuff on this that 
needs proper review.

The series has the following order:

 * patches 1-15: set everything necessary to execute hotplug scripts 
   from libxl directly.

 * patches 16-25: add necessary libxl functions to delegate hotplug 
   addition to a different daemon

 * patches 26-29: introduce xldeviced and start using it by default.

Patch 20 contains a good description of the interaction between xl and 
xldeviced, and the xenstore entries used to accomplish this task.