Prepare for extending the block device ring to allow request
specific fields, by moving the request specific fields for
reads, writes and barrier requests to a union member.
Acked-by: NJens Axboe <jaxboe@fusionio.com>
Signed-off-by: NOwen Smith <owen.smith@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Add Xen interface header files. These are taken fairly directly from
the Xen tree, but somewhat rearranged to suit the kernel's conventions.

Define macros and inline functions for doing hypercalls into the
hypervisor.
Signed-off-by: NJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: NIan Pratt <ian.pratt@xensource.com>
Signed-off-by: NChristian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: NChris Wright <chrisw@sous-sol.org>