Major Description
In order to facilitate transfer of OST and MDT performance statistics for userspace applications, such as global NRS scheduling, SCR checkpoint scheduling, QOS and allocation decisions on the MDS, etc, it is useful to transport them via obd_statfs to the clients.
The statistics should include <peak, decaying average of current> <IOPS read, IOPS write, KiB/s read, KiB/s write>.
The OSS and MDS already collect these statistics for presentation via /proc and it should be possible to include them into struct obd_statfs in newly-added fields at the end of the struct.
The stats should be fetched and printed with lfs df --stats command for all targets, but not necessarily for regular statfs() requests. With LU-10018 "MDT as a statfs() proxy", the MDT_STATFS request now has an mdt_body in the request which can be used to request different behaviour for the RPC.
