diff --git a/systrace.py b/systrace.py
index 516c0af..38443fe 100755
--- a/systrace.py
+++ b/systrace.py
@@ -10,73 +10,35 @@
 the kernel.  It creates an HTML file for visualizing the trace.
 """
 
-import errno, optparse, os, re, select, subprocess, sys, time, zlib
+import sys
 
-default_categories = 'sched gfx view dalvik webview input disk am wm'.split()
+# Make sure we're using a new enough version of Python.
+# The flags= parameter of re.sub() is new in Python 2.7.
+if sys.version_info[:2] < (2, 7):
+  print >> sys.stderr, '\nThis script requires Python 2.7 or newer.'
+  sys.exit(1)
 
-class OptionParserIgnoreErrors(optparse.OptionParser):
-  def error(self, msg):
-    pass
+# pylint: disable=g-bad-import-order,g-import-not-at-top
+import imp
+import optparse
+import os
 
-  def exit(self):
-    pass
+import util
 
-  def print_usage(self):
-    pass
 
-  def print_help(self):
-    pass
+# The default agent directory.
+DEFAULT_AGENT_DIR = 'agents'
 
-  def print_version(self):
-    pass
 
-def get_device_sdk_version():
-  getprop_args = ['adb', 'shell', 'getprop', 'ro.build.version.sdk']
+def parse_options(argv):
+  """Parses and checks the command-line options.
 
-  parser = OptionParserIgnoreErrors()
-  parser.add_option('-e', '--serial', dest='device_serial', type='string')
-  options, args = parser.parse_args()
-  if options.device_serial is not None:
-    getprop_args[1:1] = ['-s', options.device_serial]
-
-  try:
-    adb = subprocess.Popen(getprop_args, stdout=subprocess.PIPE,
-                           stderr=subprocess.PIPE)
-  except OSError:
-    print 'Missing adb?'
-    sys.exit(1)
-  out, err = adb.communicate()
-  if adb.returncode != 0:
-    print >> sys.stderr, 'Error querying device SDK-version:'
-    print >> sys.stderr, err
-    sys.exit(1)
-
-  version = int(out)
-  return version
-
-def add_adb_serial(command, serial):
-  if serial is not None:
-    command.insert(1, serial)
-    command.insert(1, '-s')
-
-def get_default_categories():
-  list_command = ['adb', 'shell', 'atrace', '--list_categories']
-  try:
-    categories_output = subprocess.check_output(list_command)
-    categories = [c.split('-')[0].strip() for c in categories_output.splitlines()]
-
-    return [c for c in categories if c in default_categories]
-  except:
-    return []
-
-def main():
-  device_sdk_version = get_device_sdk_version()
-  if device_sdk_version < 18:
-    legacy_script = os.path.join(os.path.dirname(sys.argv[0]), 'systrace-legacy.py')
-    os.execv(legacy_script, sys.argv)
-
-  usage = "Usage: %prog [options] [category1 [category2 ...]]"
-  desc = "Example: %prog -b 32768 -t 15 gfx input view sched freq"
+  Returns:
+    A tuple containing the options structure and a list of categories to
+    be traced.
+  """
+  usage = 'Usage: %prog [options] [category1 [category2 ...]]'
+  desc = 'Example: %prog -b 32768 -t 15 gfx input view sched freq'
   parser = optparse.OptionParser(usage=usage, description=desc)
   parser.add_option('-o', dest='output_file', help='write HTML to FILE',
                     default='trace.html', metavar='FILE')
@@ -85,236 +47,153 @@
   parser.add_option('-b', '--buf-size', dest='trace_buf_size', type='int',
                     help='use a trace buffer size of N KB', metavar='N')
   parser.add_option('-k', '--ktrace', dest='kfuncs', action='store',
-                    help='specify a comma-separated list of kernel functions to trace')
-  parser.add_option('-l', '--list-categories', dest='list_categories', default=False,
-                    action='store_true', help='list the available categories and exit')
+                    help='specify a comma-separated list of kernel functions '
+                    'to trace')
+  parser.add_option('-l', '--list-categories', dest='list_categories',
+                    default=False, action='store_true',
+                    help='list the available categories and exit')
   parser.add_option('-a', '--app', dest='app_name', default=None, type='string',
-                    action='store', help='enable application-level tracing for comma-separated ' +
+                    action='store',
+                    help='enable application-level tracing for comma-separated '
                     'list of app cmdlines')
   parser.add_option('--no-fix-threads', dest='fix_threads', default=True,
-                    action='store_false', help='don\'t fix missing or truncated thread names')
+                    action='store_false',
+                    help='don\'t fix missing or truncated thread names')
   parser.add_option('--no-fix-circular', dest='fix_circular', default=True,
-                    action='store_false', help='don\'t fix truncated circular traces')
-
+                    action='store_false',
+                    help='don\'t fix truncated circular traces')
+  parser.add_option('--no-compress', dest='compress_trace_data',
+                    default=True, action='store_false',
+                    help='Tell the device not to send the trace data in '
+                    'compressed form.')
   parser.add_option('--link-assets', dest='link_assets', default=False,
-                    action='store_true', help='link to original CSS or JS resources '
-                    'instead of embedding them')
+                    action='store_true',
+                    help='(deprecated)')
   parser.add_option('--from-file', dest='from_file', action='store',
-                    help='read the trace from a file (compressed) rather than running a live trace')
+                    help='read the trace from a file (compressed) rather than '
+                    'running a live trace')
   parser.add_option('--asset-dir', dest='asset_dir', default='trace-viewer',
-                    type='string', help='')
+                    type='string', help='(deprecated)')
   parser.add_option('-e', '--serial', dest='device_serial', type='string',
                     help='adb device serial number')
+  parser.add_option('--agent-dirs', dest='agent_dirs', type='string',
+                    help='the directories of additional systrace agent modules.'
+                    ' The directories should be comma separated, e.g., '
+                    '--agent-dirs=dir1,dir2,dir3. Directory |%s| is the default'
+                    ' agent directory and will always be checked.'
+                    % DEFAULT_AGENT_DIR)
 
-  options, categories = parser.parse_args()
+  options, categories = parser.parse_args(argv[1:])
 
   if options.link_assets or options.asset_dir != 'trace-viewer':
-    parser.error('--link-assets and --asset-dir is deprecated.')
+    parser.error('--link-assets and --asset-dir are deprecated.')
 
-  if options.list_categories:
-    tracer_args = ['adb', 'shell', 'atrace --list_categories']
-    expect_trace = False
-  elif options.from_file is not None:
-    tracer_args = ['cat', options.from_file]
-    expect_trace = True
-  else:
-    atrace_args = ['atrace', '-z']
-    expect_trace = True
+  if (options.trace_time is not None) and (options.trace_time <= 0):
+    parser.error('the trace time must be a positive number')
 
-    if options.trace_time is not None:
-      if options.trace_time > 0:
-        atrace_args.extend(['-t', str(options.trace_time)])
-      else:
-        parser.error('the trace time must be a positive number')
+  if (options.trace_buf_size is not None) and (options.trace_buf_size <= 0):
+    parser.error('the trace buffer size must be a positive number')
 
-    if options.trace_buf_size is not None:
-      if options.trace_buf_size > 0:
-        atrace_args.extend(['-b', str(options.trace_buf_size)])
-      else:
-        parser.error('the trace buffer size must be a positive number')
+  return (options, categories)
 
-    if options.app_name is not None:
-      atrace_args.extend(['-a', options.app_name])
 
-    if options.kfuncs is not None:
-      atrace_args.extend(['-k', options.kfuncs])
+def write_trace_html(html_filename, script_dir, agents):
+  """Writes out a trace html file.
 
-    if not categories:
-      categories = get_default_categories()
-    atrace_args.extend(categories)
+  Args:
+    html_filename: The name of the file to write.
+    script_dir: The directory containing this script.
+    agents: The systrace agents.
+  """
+  html_prefix = read_asset(script_dir, 'prefix.html')
+  html_suffix = read_asset(script_dir, 'suffix.html')
+  trace_viewer_html = read_asset(script_dir, 'systrace_trace_viewer.html')
 
-    if options.fix_threads:
-      atrace_args.extend([';', 'ps', '-t'])
-    tracer_args = ['adb', 'shell', ' '.join(atrace_args)]
+  # Open the file in binary mode to prevent python from changing the
+  # line endings.
+  html_file = open(html_filename, 'wb')
+  html_file.write(html_prefix.replace('{{SYSTRACE_TRACE_VIEWER_HTML}}',
+                                      trace_viewer_html))
 
-  if tracer_args[0] == 'adb':
-    add_adb_serial(tracer_args, options.device_serial)
+  html_file.write('<!-- BEGIN TRACE -->\n')
+  for a in agents:
+    html_file.write('  <script class="')
+    html_file.write(a.get_class_name())
+    html_file.write('" type="application/text">\n')
+    html_file.write(a.get_trace_data())
+    html_file.write('  </script>\n')
+  html_file.write('<!-- END TRACE -->\n')
+
+  html_file.write(html_suffix)
+  html_file.close()
+  print '\n    wrote file://%s\n' % os.path.abspath(html_filename)
+
+
+def create_agents(options, categories):
+  """Create systrace agents.
+
+  This function will search systrace agent modules in agent directories and
+  create the corresponding systrace agents.
+  Args:
+    options: The command-line options.
+    categories: The trace categories to capture.
+  Returns:
+    The list of systrace agents.
+  """
+  agent_dirs = [os.path.join(os.path.dirname(__file__), DEFAULT_AGENT_DIR)]
+  if options.agent_dirs:
+    agent_dirs.extend(options.agent_dirs.split(','))
+
+  agents = []
+  for agent_dir in agent_dirs:
+    if not agent_dir:
+      continue
+    for filename in os.listdir(agent_dir):
+      (module_name, ext) = os.path.splitext(filename)
+      if ext != '.py' or module_name == '__init__':
+        continue
+      (f, pathname, data) = imp.find_module(module_name, [agent_dir])
+      try:
+        module = imp.load_module(module_name, f, pathname, data)
+      finally:
+        if f:
+          f.close()
+      if module:
+        agent = module.try_create_agent(options, categories)
+        if not agent:
+          continue
+        agents.append(agent)
+  return agents
+
+
+def main():
+  options, categories = parse_options(sys.argv)
+  agents = create_agents(options, categories)
+
+  if not agents:
+    dirs = DEFAULT_AGENT_DIR
+    if options.agent_dirs:
+      dirs += ',' + options.agent_dirs
+    print >> sys.stderr, ('No systrace agent is available in directories |%s|.'
+                          % dirs)
+    sys.exit(1)
+
+  for a in agents:
+    a.start()
+
+  for a in agents:
+    a.collect_result()
+    if not a.expect_trace():
+      # Nothing more to do.
+      return
 
   script_dir = os.path.dirname(os.path.abspath(sys.argv[0]))
+  write_trace_html(options.output_file, script_dir, agents)
 
-  html_filename = options.output_file
-
-  adb = subprocess.Popen(tracer_args, stdout=subprocess.PIPE,
-                         stderr=subprocess.PIPE)
-
-  result = None
-  data = []
-
-  # Read the text portion of the output and watch for the 'TRACE:' marker that
-  # indicates the start of the trace data.
-  while result is None:
-    ready = select.select([adb.stdout, adb.stderr], [], [adb.stdout, adb.stderr])
-    if adb.stderr in ready[0]:
-      err = os.read(adb.stderr.fileno(), 4096)
-      sys.stderr.write(err)
-      sys.stderr.flush()
-    if adb.stdout in ready[0]:
-      out = os.read(adb.stdout.fileno(), 4096)
-      parts = out.split('\nTRACE:', 1)
-
-      txt = parts[0].replace('\r', '')
-      if len(parts) == 2:
-        # The '\nTRACE:' match stole the last newline from the text, so add it
-        # back here.
-        txt += '\n'
-      sys.stdout.write(txt)
-      sys.stdout.flush()
-
-      if len(parts) == 2:
-        data.append(parts[1])
-        sys.stdout.write("downloading trace...")
-        sys.stdout.flush()
-        break
-
-    result = adb.poll()
-
-  # Read and buffer the data portion of the output.
-  while True:
-    ready = select.select([adb.stdout, adb.stderr], [], [adb.stdout, adb.stderr])
-    keepReading = False
-    if adb.stderr in ready[0]:
-      err = os.read(adb.stderr.fileno(), 4096)
-      if len(err) > 0:
-        keepReading = True
-        sys.stderr.write(err)
-        sys.stderr.flush()
-    if adb.stdout in ready[0]:
-      out = os.read(adb.stdout.fileno(), 4096)
-      if len(out) > 0:
-        keepReading = True
-        data.append(out)
-
-    if result is not None and not keepReading:
-      break
-
-    result = adb.poll()
-
-  if result == 0:
-    if expect_trace:
-      data = ''.join(data)
-
-      # Collapse CRLFs that are added by adb shell.
-      if data.startswith('\r\n'):
-        data = data.replace('\r\n', '\n')
-
-      # Skip the initial newline.
-      data = data[1:]
-
-      if not data:
-        print >> sys.stderr, ('No data was captured.  Output file was not ' +
-          'written.')
-        sys.exit(1)
-      else:
-        # Indicate to the user that the data download is complete.
-        print " done\n"
-
-      # Extract the thread list dumped by ps.
-      threads = {}
-      if options.fix_threads:
-        parts = re.split('USER +PID +PPID +VSIZE +RSS +WCHAN +PC +NAME', data, 1)
-        if len(parts) == 2:
-          data = parts[0]
-          for line in parts[1].splitlines():
-            cols = line.split(None, 8)
-            if len(cols) == 9:
-              tid = int(cols[1])
-              name = cols[8]
-              threads[tid] = name
-
-      # Decompress and preprocess the data.
-      out = zlib.decompress(data)
-      if options.fix_threads:
-        def repl(m):
-          tid = int(m.group(2))
-          if tid > 0:
-            name = threads.get(tid)
-            if name is None:
-              name = m.group(1)
-              if name == '<...>':
-                name = '<' + str(tid) + '>'
-              threads[tid] = name
-            return name + '-' + m.group(2)
-          else:
-            return m.group(0)
-        out = re.sub(r'^\s*(\S+)-(\d+)', repl, out, flags=re.MULTILINE)
-
-      if options.fix_circular:
-        out = fix_circular_traces(out)
-
-      html_prefix = read_asset(script_dir, 'prefix.html')
-      html_suffix = read_asset(script_dir, 'suffix.html')
-      trace_viewer_html = read_asset(script_dir, 'systrace_trace_viewer.html')
-
-      html_file = open(html_filename, 'w')
-      html_file.write(
-        html_prefix.replace("{{SYSTRACE_TRACE_VIEWER_HTML}}", trace_viewer_html))
-
-      html_file.write('<!-- BEGIN TRACE -->\n' +
-          '  <script class="trace-data" type="application/text">\n')
-      html_file.write(out)
-      html_file.write('  </script>\n<!-- END TRACE -->\n')
-
-      html_file.write(html_suffix)
-      html_file.close()
-      print "\n    wrote file://%s\n" % os.path.abspath(options.output_file)
-
-  else: # i.e. result != 0
-    print >> sys.stderr, 'adb returned error code %d' % result
-    sys.exit(1)
 
 def read_asset(src_dir, filename):
   return open(os.path.join(src_dir, filename)).read()
 
-def fix_circular_traces(out):
-  """Fix inconsistentcies in traces due to circular buffering.
-
-  The circular buffers are kept per CPU, so it is not guaranteed that the
-  beginning of a slice is overwritten before the end. To work around this, we
-  throw away the prefix of the trace where not all CPUs have events yet."""
-
-  # If any of the CPU's buffers have filled up and
-  # older events have been dropped, the kernel
-  # emits markers of the form '##### CPU 2 buffer started ####' on
-  # the line before the first event in the trace on that CPU.
-  #
-  # No such headers are emitted if there were no overflows or the trace
-  # was captured with non-circular buffers.
-  buffer_start_re = re.compile(r'^#+ CPU \d+ buffer started', re.MULTILINE)
-
-  start_of_full_trace = 0
-
-  while True:
-    result = buffer_start_re.search(out, start_of_full_trace + 1)
-    if result:
-      start_of_full_trace = result.start()
-    else:
-      break
-
-  if start_of_full_trace > 0:
-    # Need to keep the header intact to make the importer happy.
-    end_of_header = re.search(r'^[^#]', out, re.MULTILINE).start()
-    out = out[:end_of_header] + out[start_of_full_trace:]
-  return out
 
 if __name__ == '__main__':
   main()