Set argv[0] of the buildbot master process to the name of the master.

scripts/master/master_utils.py

Index: scripts/master/master_utils.py
diff --git a/scripts/master/master_utils.py b/scripts/master/master_utils.py
index 190bf7966901ed7c25d91ee6f82fbca3c789c69e..3139e8c6275d8c164c30accc24910e67ef61e1fe 100644
--- a/scripts/master/master_utils.py
+++ b/scripts/master/master_utils.py
@@ -2,9 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import ctypes
+import ctypes.util
 import os
 import random
 import re
+import sys
 
 import buildbot
 from buildbot import interfaces, util
@@ -474,6 +477,11 @@ def AutoSetupMaster(c, active_master, mail_notifier=False,
   if active_master.buildbucket_bucket and active_master.service_account_path:
     SetupBuildbucket(c, active_master)
 
+  # TODO(dsansome): enable this on all masters if it works, remove completely
+  # if it doesn't.
+  if GetMastername() in {'chromium.infra', 'chromium.infra.cron'}:
+    SetMasterProcessName()
+
 
 def SetupBuildbucket(c, active_master):
   def params_hook(params, build):
@@ -659,3 +667,34 @@ class PreferredBuilderNextSlaveFunc(object):
         s for s in slave_builders
         if s.slave.properties.getProperty('preferred_builder') == builder.name]
     return random.choice(preferred_slaves or slave_builders)
+
+
+def SetMasterProcessName():
+  """Sets the name of this process to the name of the master.  Linux only."""
+
+  if sys.platform != 'linux2':
+    sys.exit(2)
+    return
+
+  SetCommandLine("master: %s" % GetMastername())
+
+
+def SetCommandLine(cmdline):
+  # Get the current commandline.
+  argc = ctypes.c_int()
+  argv = ctypes.POINTER(ctypes.c_char_p)()
+  ctypes.pythonapi.Py_GetArgcArgv(ctypes.byref(argc), ctypes.byref(argv))
+
+  # Calculate its length.
+  cmdlen = sum([len(argv[i]) for i in xrange(0, argc.value)]) + argc.value
+
+  # Pad the cmdline string to the required length.  If it's longer than the
+  # currentl commandline, truncate it.
+  if len(cmdline) >= cmdlen:
+    new_cmdline = ctypes.c_char_p(cmdline[:cmdlen-1] + '\0')
+  else:
+    new_cmdline = ctypes.c_char_p(cmdline.ljust(cmdlen, '\0'))
+
+  # Replace the old commandline.
+  libc = ctypes.CDLL(ctypes.util.find_library('c'))
+  libc.memcpy(argv.contents, new_cmdline, cmdlen)