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#!/usr/bin/env python3
#
# KVM Flight Recorder - ring buffer tracing script
#
# Copyright (C) 2012 IBM Corp
#
# Author: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
#
# This script provides a command-line interface to kvm ftrace and is designed
# to be used as a flight recorder that is always running. To start in-memory
# recording:
#
# sudo kvm_flightrecorder start 8192 # 8 MB per-cpu ring buffers
#
# The per-cpu ring buffer size can be given in KB as an optional argument to
# the 'start' subcommand.
#
# To stop the flight recorder:
#
# sudo kvm_flightrecorder stop
#
# To dump the contents of the flight recorder (this can be done when the
# recorder is stopped or while it is running):
#
# sudo kvm_flightrecorder dump >/path/to/dump.txt
#
# To observe the trace while it is running, use the 'tail' subcommand:
#
# sudo kvm_flightrecorder tail
#
# Note that the flight recorder may impact overall system performance by
# consuming CPU cycles. No disk I/O is performed since the ring buffer holds a
# fixed-size in-memory trace.
import sys
import os
tracing_dir = '/sys/kernel/debug/tracing'
def trace_path(*args):
return os.path.join(tracing_dir, *args)
def write_file(path, data):
open(path, 'wb').write(data)
def enable_event(subsystem, event, enable):
write_file(trace_path('events', subsystem, event, 'enable'), '1' if enable else '0')
def enable_subsystem(subsystem, enable):
write_file(trace_path('events', subsystem, 'enable'), '1' if enable else '0')
def start_tracing():
enable_subsystem('kvm', True)
write_file(trace_path('tracing_on'), '1')
def stop_tracing():
write_file(trace_path('tracing_on'), '0')
enable_subsystem('kvm', False)
write_file(trace_path('events', 'enable'), '0')
write_file(trace_path('current_tracer'), 'nop')
def dump_trace():
tracefile = open(trace_path('trace'), 'r')
try:
lines = True
while lines:
lines = tracefile.readlines(64 * 1024)
sys.stdout.writelines(lines)
except KeyboardInterrupt:
pass
def tail_trace():
try:
for line in open(trace_path('trace_pipe'), 'r'):
sys.stdout.write(line)
except KeyboardInterrupt:
pass
def usage():
print('Usage: %s start [buffer_size_kb] | stop | dump | tail' % sys.argv[0])
print('Control the KVM flight recorder tracing.')
sys.exit(0)
def main():
if len(sys.argv) < 2:
usage()
cmd = sys.argv[1]
if cmd == '--version':
print('kvm_flightrecorder version 1.0')
sys.exit(0)
if not os.path.isdir(tracing_dir):
print('Unable to tracing debugfs directory, try:')
print('mount -t debugfs none /sys/kernel/debug')
sys.exit(1)
if not os.access(tracing_dir, os.W_OK):
print('Unable to write to tracing debugfs directory, please run as root')
sys.exit(1)
if cmd == 'start':
stop_tracing() # clean up first
if len(sys.argv) == 3:
try:
buffer_size_kb = int(sys.argv[2])
except ValueError:
print('Invalid per-cpu trace buffer size in KB')
sys.exit(1)
write_file(trace_path('buffer_size_kb'), str(buffer_size_kb))
print('Per-CPU ring buffer size set to %d KB' % buffer_size_kb)
start_tracing()
print('KVM flight recorder enabled')
elif cmd == 'stop':
stop_tracing()
print('KVM flight recorder disabled')
elif cmd == 'dump':
dump_trace()
elif cmd == 'tail':
tail_trace()
else:
usage()
if __name__ == '__main__':
sys.exit(main())
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