block: Track DISCARD statistics and output them in stat and diskstat

Add tracking of REQ_OP_DISCARD ios to the partition statistics and
append them to the various stat files in /sys as well as
/proc/diskstats.  These are tracked with the same four stats as reads
and writes:

Number of discard ios completed.
Number of discard ios merged
Number of discard sectors completed
Milliseconds spent on discard requests

This is done via adding a new STAT_DISCARD define to genhd.h and then
using it to index that stat field for discard requests.

tj: Refreshed on top of v4.17 and other previous updates.

Signed-off-by: Michael Callahan <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Cc: Andy Newell <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions