[PATCH 0/4] (Refactored) VHD Support Addition

[Ben Guthro <bguthro@virtualiron.com>]

[PATCH 0/4] (Refactored) VHD Support addition
The patches that follow implement Microsoft's VHD format support, and
apply to xen-unstable.hg CS 15414:3827b12d24dd
Per Mark McLoughlin's suggestions - these have been reworked to use the 
tapaio wrapper.

This is based on the VHD format spec covered by Microsoft's "Open
Specification Promise":
http://www.microsoft.com/interop/osp/default.mspx
MS VHD Spec can be found at the following link:
http://download.microsoft.com/download/f/f/e/ffef50a5-07dd-4cf8-aaa3-442c0673a029/Virtual%20Hard%20Disk%20Format%20Spec_10_18_06.doc

It is divided up into the following patches:
qemu-vhd-support.patch        [1/4]
tapdisk-vhd-support.patch     [2/4]
blktap-fixes.patch            [3/4]
vdisk-support.patch           [4/4]

### libvdisk ####
These patches implement a shared library (libvdisk) between qemu, and
blktap which can be expanded upon for additional formats in the future.
This was done in order to avoid code duplcation between the two areas.
At this time, it only supports the vhd format.

### vdisk_tool ###
The vdisk_tool provides a means of creating, and converting vhd files.
Like libvdisk, it is designed with future support of additional formats
in mind, but currently only supports vhd.

Usage: vdisk_tool OPTIONS -# <format-specific options> <filename>
  OPTIONS:
    [-f <format>] [-C] [-H] [-M] [-D <block> [-b <num_blocks>] -o outfile]]
    -C        Create a vdisk
    -H        Read vdisk headers from file
    -M        Modify a vdisk
    -D        Dump a vhd
      block       first block to read (required)
      num_blocks       number of blocks to read. If not
                specified, whole file will be read
      outfile       output file. If not specified,
                stdout is used
    

With this, you can convert foo.vhd to raw volume /dev/foo/bar:
      vdisk_tool -D 0 -o /dev/foo/bar foo.vhd

To convert foo.vhd to fixed bar.vhd
      vdisk_tool -D 0 -o bar.vhd foo.vhd
      vdisk_tool -C -# -S <sizeB> -f bar.vhd

To read blocks 2 through 6 from foo.vhd to stdout:
      vdisk_tool -D 2 -b 5 foo.vhd