[PATCH 0 of 6] dm-userspace xen integration

[Ryan Grimm <grimm@us.ibm.com>]

In June, Dan Smith posted a patch to add dm-userspace to the -xen kernel*.
Since then, an io completion notification mechanism for metadata writing has
been added*.  The kernel module, along with the the tools, consistently pass
fsstress and dbench tests on both x86_64 and x86_32.

These patches integrate dm-userspace into the xen tree and allow a cow domain
to be created.  Hopefully some people can start experimenting with it and we
look forward to hearing some feedback.

Cowd and its associated plugins are a bit rough right now, but they work, and
we plan on smoothing things out in the near future.

This patch is broken up into 6 parts:

[1/6]: A patch to the xen kernel in the patches/ directory.  Also the default
config files will build dm_userspace as a module.

[2/6]: Adds the base for cowd, the userspace tool, to the tools directory.

[3/6]: Adds internal libdmu support to cowd

[4/6]: The dscow plugin for cowd

[5/6]: The qcow plugin for cowd

[6/6]: A script to start the dm-userspace backend as well as an xm example
configuration file.

*http://lists.xensource.com/archives/html/xen-devel/2006-06/msg00372.html
*http://lists.xensource.com/archives/html/xen-devel/2006-06/msg00773.html