Linux : blktrace Invalid debug path /sys/kernel/debug: 0/Success

Problem:
# blktrace -d /dev/sda -o - | blkparse -i -
Invalid debug path /sys/kernel/debug: 0/Success

Solution:
# mount -t debugfs debugfs /sys/kernel/debug

 # blktrace -d /dev/sda -o - | blkparse -i -  (same as btrace /dev/sda )
  8,2   27        1     0.000000000 18095  A  WS 979109888 + 8 <- (253,1) 962330624
  8,0   27        2     0.000000901 18095  A  WS 980135936 + 8 <- (8,2) 979109888
  8,0   27        3     0.000001759 18095  Q  WS 980135936 + 8 [mysqld]
  8,0   27        4     0.000012107 18095  G  WS 980135936 + 8 [mysqld]
  8,0   27        5     0.000014817 18095  P   N [mysqld]
  8,0   27        6     0.000015845 18095  I  WS 980135936 + 8 [mysqld]
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