[PATCH] btt: seek additions

[PATCH] btt: seek additions

Added seek analysis to btt:

==================== Device Seek Information ====================

       DEV |          NSEEKS            MEAN          MEDIAN | MODE
---------- | --------------- --------------- --------------- | ---------------
 (  8, 16) |           15573      10297802.6               0 | 0(10710)

Shows the:
- Device (major, minor)

- Number of seeks (IOs issued to driver)

- Average (mean) of sector differences IO-to-IO

- Median seek (sector difference)

- Mode(s) - showing the mode and the number of times it occurred, thus in
  this example we see 68.8% of the "seeks" were contiguous (or overlapping).

Also added in the ability to dump all read and write seek values:

[ -s <output name> | --seeks=<output name> ]

Will create files with the name:

seek_<mjr,mnr>_[rw].dat

like:

seek_008,016_r.dat
seek_008,016_w.dat

Which contain relative sector offsets for reads and writes respectively.

Signed-off-by: Jens Axboe <axboe@kernel.dk>