Linux sysfs

I was researching which kernel counters where available for disks, when I bumped into sysfs. Sysfs exposes kernel data structures, the relationship between those structures is represented as directory structure 


  block/
  bus/
  class/
  dev/
  devices/
  firmware/
  net/
  fs/

As I was interested in disk metrics I just drilled down to block, and found stats /sys/block/<disk>/stat 

  What: /sys/block/<disk>/stat
  Date: February 2008
  Contact: Jerome Marchand 
   Description:
   The /sys/block//stat files displays the I/O
    statistics of disk . They contain 11 fields:

     == ==============================================
     1 reads completed successfully
     2 reads merged
     3 sectors read
     4 time spent reading (ms)
     5 writes completed
     6 writes merged
     7 sectors written
     8 time spent writing (ms)
     9 I/Os currently in progress
     10 time spent doing I/Os (ms)
     11 weighted time spent doing I/Os (ms)
     12 discards completed
     13 discards merged
     14 sectors discarded
     15 time spent discarding (ms)
     16 flush requests completed
     17 time spent flushing (ms)
     == ==============================================

     For more details refer Documentation/admin-guide/iostats.rst

So just reading the stat file returns the counters: 

  neirac@alma nvme0n1]$ cat /sys/block/nvme0n1/stat
  13534 11 683573 3185 14941 17536 2731548 58278 0 14339 61464 0 0 0 0 0 0



References

SYSFS kernel notes