[PATCH 0 of 7] blktap2: The tap-ctl userspace control utility and library

[Daniel Stodden <daniel.stodden@citrix.com>]

Hi.

Apart from removing some dead code and tidying up tapdisk-vbd a
little, the bigger introduces our new tap-ctl utility code.

The code aims to be a complete replacement for the original blktap2
control path, run through sysfs. Fully implemented in userspace, all
tapdisks now gained a small IPC layer on top of Unix domain sockets.

Sample usage:

# tap-ctl allocate
/dev/xen/blktap-2/tapdev0

# tap-ctl spawn
tapdisk spawned with pid 4168

# tap-ctl list
    4168  -    -          - -
       -  0    -          - -

# tap-ctl attach -p 4168 -m 0
# tap-ctl list
    4168  0    0          - -

# tap-ctl open -p 4168 -m 0 -a aio:/var/tmp/lenny.ext

# tap-ctl list
    4168  0    0        aio /var/tmp/lenny.ext

# tap-ctl close -p 4168 -m 0
# tap-ctl detach -p 4168 -m 0
# tap-ctl free -m 0

The above example is a bit noisy, because it's mediating between minor
number (block devices), tapdisks and tapdisk VBDs (the tapdisk I/O
queue running a bdev) in detail. 

There are shortcuts. At the same time, the low-level interface should
be general enough to stay extensible, and help accomodate some of the
more esoteric features, like shared images and/or multiple VBDs
sharing the same tapdisk.

Cheers,
Daniel