scripts/kvm/kvm_flightrecorder

   1 #!/usr/bin/env python3
   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 import sys
  36 import os
  37
  38 tracing_dir = '/sys/kernel/debug/tracing'
  39
  40 def trace_path(*args):
  41     return os.path.join(tracing_dir, *args)
  42
  43 def write_file(path, data):
  44     open(path, 'wb').write(data)
  45
  46 def enable_event(subsystem, event, enable):
  47     write_file(trace_path('events', subsystem, event, 'enable'), '1' if enable else '0')
  48
  49 def enable_subsystem(subsystem, enable):
  50     write_file(trace_path('events', subsystem, 'enable'), '1' if enable else '0')
  51
  52 def start_tracing():
  53     enable_subsystem('kvm', True)
  54     write_file(trace_path('tracing_on'), '1')
  55
  56 def stop_tracing():
  57     write_file(trace_path('tracing_on'), '0')
  58     enable_subsystem('kvm', False)
  59     write_file(trace_path('events', 'enable'), '0')
  60     write_file(trace_path('current_tracer'), 'nop')
  61
  62 def dump_trace():
  63     tracefile = open(trace_path('trace'), 'r')
  64     try:
  65         lines = True
  66         while lines:
  67             lines = tracefile.readlines(64 * 1024)
  68             sys.stdout.writelines(lines)
  69     except KeyboardInterrupt:
  70         pass
  71
  72 def tail_trace():
  73     try:
  74         for line in open(trace_path('trace_pipe'), 'r'):
  75             sys.stdout.write(line)
  76     except KeyboardInterrupt:
  77         pass
  78
  79 def usage():
  80     print('Usage: %s start [buffer_size_kb] | stop | dump | tail' % sys.argv[0])
  81     print('Control the KVM flight recorder tracing.')
  82     sys.exit(0)
  83
  84 def main():
  85     if len(sys.argv) < 2:
  86         usage()
  87
  88     cmd = sys.argv[1]
  89     if cmd == '--version':
  90         print('kvm_flightrecorder version 1.0')
  91         sys.exit(0)
  92
  93     if not os.path.isdir(tracing_dir):
  94         print('Unable to tracing debugfs directory, try:')
  95         print('mount -t debugfs none /sys/kernel/debug')
  96         sys.exit(1)
  97     if not os.access(tracing_dir, os.W_OK):
  98         print('Unable to write to tracing debugfs directory, please run as root')
  99         sys.exit(1)
 100
 101     if cmd == 'start':
 102         stop_tracing() # clean up first
 103
 104         if len(sys.argv) == 3:
 105             try:
 106                 buffer_size_kb = int(sys.argv[2])
 107             except ValueError:
 108                 print('Invalid per-cpu trace buffer size in KB')
 109                 sys.exit(1)
 110             write_file(trace_path('buffer_size_kb'), str(buffer_size_kb))
 111             print('Per-CPU ring buffer size set to %d KB' % buffer_size_kb)
 112
 113         start_tracing()
 114         print('KVM flight recorder enabled')
 115     elif cmd == 'stop':
 116         stop_tracing()
 117         print('KVM flight recorder disabled')
 118     elif cmd == 'dump':
 119         dump_trace()
 120     elif cmd == 'tail':
 121         tail_trace()
 122     else:
 123         usage()
 124
 125 if __name__ == '__main__':
 126     sys.exit(main())