Add utilities for liveliness lock files

To request resources from WConfD, requesters have to provide
the name of a file they own an exclusive lock on. In this way,
their death can be detected. Add utility functions to obtain
such a file name.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

Makefile.am

@@ -509,6 +509,7 @@ utils_PYTHON = \
 	lib/utils/filelock.py \
 	lib/utils/hash.py \
 	lib/utils/io.py \
+	lib/utils/livelock.py \
 	lib/utils/log.py \
 	lib/utils/lvm.py \
 	lib/utils/mlock.py \

lib/utils/__init__.py

@@ -47,6 +47,7 @@ from ganeti.utils.algo import *
 from ganeti.utils.filelock import *
 from ganeti.utils.hash import *
 from ganeti.utils.io import *
+from ganeti.utils.livelock import *
 from ganeti.utils.log import *
 from ganeti.utils.lvm import *
 from ganeti.utils.mlock import *

lib/utils/livelock.py

+#
+#
+
+# Copyright (C) 2014 Google Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+"""Lockfiles to prove liveliness
+
+When requesting resources, like locks, from wconfd, requesters have
+to provide the name of a file they own an exclusive lock on, to prove
+that they are still alive. Provide methods to obtain such a file.
+"""
+
+import fcntl
+import os
+import struct
+import time
+
+from ganeti import pathutils
+
+
+class LiveLock(object):
+  """Utility for a lockfile needed to request resources from WconfD.
+
+  """
+  def __init__(self, name=None):
+    if name is None:
+      name = "pid%d_" % os.getpid()
+    # to avoid reusing existing lock files, extend name
+    # by the current time
+    name = "%s_%d" % (name, int(time.time()))
+    fname = os.path.join(pathutils.LIVELOCK_DIR, name)
+    self.lockfile = open(fname, 'w')
+    fcntl.fcntl(self.lockfile, fcntl.F_SETLKW,
+                struct.pack('hhllhh', fcntl.F_WRLCK, 0, 0, 0, 0, 0))
+
+  def close(self):
+    """Close the lockfile and clean it up.
+
+    """
+    self.lockfile.close()
+    os.remove(self.lockfile.name)