Mounting images in Dom0 using the blktap2 driver

Tap (and blkback) disks are also mountable in Dom0 without requiring an

active VM to attach

The syntax is -

  tapdisk2 -n <type>:<full path to file>

For example -

  tapdisk2  -n aio:/home/images/rawFile.img

When successful the location of the new device will be provided by
tapdisk2 to stdout and tapdisk2 will terminate.  From that point
forward control of the device is provided through sysfs in the
directory-

  /sys/class/blktap2/blktap#/

Where # is a blktap2 device number present in the path that tapdisk2
printed before terminating.  The sysfs interface is largely intuitive,
for example, to remove tap device 0 one would-

  echo 1 > /sys/class/blktap2/blktap0/remove

Similarly, a pause control is available, which is can be used to plug
the request queue of a live running guest.

Previous versions of blktap mounted devices in dom0 by using blkfront
in dom0 and the xm block-attach command.  This approach is still
available, though slightly more cumbersome.