Add `slave_alloc_update` tool.

scripts/tools/slave_alloc_update.py

Index: scripts/tools/slave_alloc_update.py
diff --git a/scripts/tools/slave_alloc_update.py b/scripts/tools/slave_alloc_update.py
new file mode 100755
index 0000000000000000000000000000000000000000..7e2f94504d6c7e62c3d6c0a5f9818bc3ad660544
--- /dev/null
+++ b/scripts/tools/slave_alloc_update.py
@@ -0,0 +1,81 @@
+#!/usr/bin/env python
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Command-line tool to update slave allocation JSON for slave pools that are
+managed by `<build>/scripts/common/slave_alloc.py`.
+
+This script is directed at a master, and will:
+  1) Load the master's `slaves.cfg` and process it.
+  2) For each identified SlaveAllocator instance, regenerate the slave pool JSON
+     file.
+"""
+
+import argparse
+import logging
+import os
+import sys
+
+import common.chromium_utils
+import common.env
+import common.slave_alloc
+
+
+def _UpdateSlaveAlloc(master_dir, sa):
+  logging.info('Updating slaves for master "%s": [%s]',
+               os.path.basename(master_dir), sa.state_path)
+  with common.chromium_utils.MasterEnvironment(master_dir):
+    sa.SaveState()
+
+
+def _UpdateMaster(master_name):
+  master_dir = common.chromium_utils.MasterPath(master_name)
+  slaves_cfg_path = os.path.join(os.path.abspath(master_dir), 'slaves.cfg')
+  if not os.path.isfile(slaves_cfg_path):
+    raise ValueError('Master directory does not contain "slaves.cfg": %s' % (
+                     master_dir,))
+
+  logging.debug('Loading "slaves.cfg" from: [%s]', slaves_cfg_path)
+  cfg = common.chromium_utils.ParsePythonCfg(slaves_cfg_path, fail_hard=False)
+
+  updated = False
+  for name, sa in (cfg or {}).iteritems():
+    if isinstance(sa, common.slave_alloc.SlaveAllocator):
+      logging.debug('Identified slave allocator variable [%s]', name)
+      _UpdateSlaveAlloc(master_dir, sa)
+      updated = True
+  return updated
+
+
+def main(argv):
+  parser = argparse.ArgumentParser()
+  parser.add_argument('-v', '--verbose',
+      action='count', default=0,
+      help='Increase verbosity. This can be specified multiple times.')
+  parser.add_argument('masters', metavar='NAME', nargs='+',
+      help='Name of the master to update.')
+  args = parser.parse_args(argv)
+
+  # Configure logging verbosity.
+  if args.verbose == 0:
+    level = logging.WARNING
+  elif args.verbose == 1:
+    level = logging.INFO
+  else:
+    level = logging.DEBUG
+  logging.getLogger().setLevel(level)
+
+  # Update each master directory.
+  for name in args.masters:
+    if not _UpdateMaster(name):
+      raise ValueError('No slave allocators identified for [%s]' % (name,))
+
+
+if __name__ == '__main__':
+  logging.basicConfig()
+  try:
+    sys.exit(main(sys.argv[1:]))
+  except Exception as e:
+    logging.exception('Uncaught exception encountered during execution: %s', e)
+    sys.exit(2)