scripts/kvm/kvm_flightrecorder

   1 #!/usr/bin/env python
   2 #
   3 # KVM Flight Recorder - ring buffer tracing script
   4 #
   5 # Copyright (C) 2012 IBM Corp
   6 #
   7 # Author: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
   8 #
   9 # This script provides a command-line interface to kvm ftrace and is designed
  10 # to be used as a flight recorder that is always running.  To start in-memory
  11 # recording:
  12 #
  13 # sudo kvm_flightrecorder start 8192  # 8 MB per-cpu ring buffers
  14 #
  15 # The per-cpu ring buffer size can be given in KB as an optional argument to
  16 # the 'start' subcommand.
  17 #
  18 # To stop the flight recorder:
  19 #
  20 # sudo kvm_flightrecorder stop
  21 #
  22 # To dump the contents of the flight recorder (this can be done when the
  23 # recorder is stopped or while it is running):
  24 #
  25 # sudo kvm_flightrecorder dump >/path/to/dump.txt
  26 #
  27 # To observe the trace while it is running, use the 'tail' subcommand:
  28 #
  29 # sudo kvm_flightrecorder tail
  30 #
  31 # Note that the flight recorder may impact overall system performance by
  32 # consuming CPU cycles.  No disk I/O is performed since the ring buffer holds a
  33 # fixed-size in-memory trace.
  34
  35 from __future__ import print_function
  36 import sys
  37 import os
  38
  39 tracing_dir = '/sys/kernel/debug/tracing'
  40
  41 def trace_path(*args):
  42     return os.path.join(tracing_dir, *args)
  43
  44 def write_file(path, data):
  45     open(path, 'wb').write(data)
  46
  47 def enable_event(subsystem, event, enable):
  48     write_file(trace_path('events', subsystem, event, 'enable'), '1' if enable else '0')
  49
  50 def enable_subsystem(subsystem, enable):
  51     write_file(trace_path('events', subsystem, 'enable'), '1' if enable else '0')
  52
  53 def start_tracing():
  54     enable_subsystem('kvm', True)
  55     write_file(trace_path('tracing_on'), '1')
  56
  57 def stop_tracing():
  58     write_file(trace_path('tracing_on'), '0')
  59     enable_subsystem('kvm', False)
  60     write_file(trace_path('events', 'enable'), '0')
  61     write_file(trace_path('current_tracer'), 'nop')
  62
  63 def dump_trace():
  64     tracefile = open(trace_path('trace'), 'r')
  65     try:
  66         lines = True
  67         while lines:
  68             lines = tracefile.readlines(64 * 1024)
  69             sys.stdout.writelines(lines)
  70     except KeyboardInterrupt:
  71         pass
  72
  73 def tail_trace():
  74     try:
  75         for line in open(trace_path('trace_pipe'), 'r'):
  76             sys.stdout.write(line)
  77     except KeyboardInterrupt:
  78         pass
  79
  80 def usage():
  81     print('Usage: %s start [buffer_size_kb] | stop | dump | tail' % sys.argv[0])
  82     print('Control the KVM flight recorder tracing.')
  83     sys.exit(0)
  84
  85 def main():
  86     if len(sys.argv) < 2:
  87         usage()
  88
  89     cmd = sys.argv[1]
  90     if cmd == '--version':
  91         print('kvm_flightrecorder version 1.0')
  92         sys.exit(0)
  93
  94     if not os.path.isdir(tracing_dir):
  95         print('Unable to tracing debugfs directory, try:')
  96         print('mount -t debugfs none /sys/kernel/debug')
  97         sys.exit(1)
  98     if not os.access(tracing_dir, os.W_OK):
  99         print('Unable to write to tracing debugfs directory, please run as root')
 100         sys.exit(1)
 101
 102     if cmd == 'start':
 103         stop_tracing() # clean up first
 104
 105         if len(sys.argv) == 3:
 106             try:
 107                 buffer_size_kb = int(sys.argv[2])
 108             except ValueError:
 109                 print('Invalid per-cpu trace buffer size in KB')
 110                 sys.exit(1)
 111             write_file(trace_path('buffer_size_kb'), str(buffer_size_kb))
 112             print('Per-CPU ring buffer size set to %d KB' % buffer_size_kb)
 113
 114         start_tracing()
 115         print('KVM flight recorder enabled')
 116     elif cmd == 'stop':
 117         stop_tracing()
 118         print('KVM flight recorder disabled')
 119     elif cmd == 'dump':
 120         dump_trace()
 121     elif cmd == 'tail':
 122         tail_trace()
 123     else:
 124         usage()
 125
 126 if __name__ == '__main__':
 127     sys.exit(main())