jstore: Add queue helper functions

This will be used to move common code out of jqueue.

Reviewed-by: iustinp

Makefile.am

@@ -71,6 +71,7 @@ pkgpython_PYTHON = \
 	lib/errors.py \
 	lib/http.py \
 	lib/jqueue.py \
+	lib/jstore.py \
 	lib/locking.py \
 	lib/logger.py \
 	lib/luxi.py \

lib/jstore.py

+#
+#
+
+# Copyright (C) 2006, 2007 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.
+
+
+"""Module implementing the job queue handling."""
+
+import os
+import logging
+import errno
+import re
+
+from ganeti import constants
+from ganeti import errors
+from ganeti import utils
+
+
+def _ReadNumericFile(file_name):
+  """Reads a file containing a number.
+
+  @rtype: None or int
+  @return: None if file is not found, otherwise number
+
+  """
+  try:
+    fd = open(file_name, "r")
+  except IOError, err:
+    if err.errno in (errno.ENOENT, ):
+      return None
+    raise
+
+  try:
+    return int(fd.read(128))
+  finally:
+    fd.close()
+
+
+def ReadSerial():
+  """Read the serial file.
+
+  The queue should be locked while this function is called.
+
+  """
+  return _ReadNumericFile(constants.JOB_QUEUE_SERIAL_FILE)
+
+
+def ReadVersion():
+  """Read the queue version.
+
+  The queue should be locked while this function is called.
+
+  """
+  return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE)
+
+
+def InitAndVerifyQueue(exclusive):
+  """Open and lock job queue.
+
+  If necessary, the queue is automatically initialized.
+
+  @type exclusive: bool
+  @param exclusive: Whether to lock the queue in exclusive mode. Shared
+                    mode otherwise.
+  @rtype: utils.FileLock
+  @return: Lock object for the queue. This can be used to change the
+           locking mode.
+
+  """
+  # Make sure our directories exists
+  for path in (constants.QUEUE_DIR, constants.JOB_QUEUE_ARCHIVE_DIR):
+    try:
+      os.mkdir(path, 0700)
+    except OSError, err:
+      if err.errno not in (errno.EEXIST, ):
+        raise
+
+  # Lock queue
+  queue_lock = utils.FileLock(constants.JOB_QUEUE_LOCK_FILE)
+  try:
+    # Determine locking function and call it
+    if exclusive:
+      fn = queue_lock.Exclusive
+    else:
+      fn = queue_lock.Shared
+
+    fn(blocking=False)
+
+    # Verify version
+    version = ReadVersion()
+    if version is None:
+      # Write new version file
+      utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE,
+                      data="%s\n" % constants.JOB_QUEUE_VERSION)
+
+      # Read again
+      version = ReadVersion()
+
+    if version != constants.JOB_QUEUE_VERSION:
+      raise errors.JobQueueError("Found job queue version %s, expected %s",
+                                 version, constants.JOB_QUEUE_VERSION)
+
+    serial = ReadSerial()
+    if serial is None:
+      # Write new serial file
+      utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE,
+                      data="%s\n" % 0)
+
+      # Read again
+      serial = ReadSerial()
+
+    if serial is None:
+      # There must be a serious problem
+      raise errors.JobQueueError("Can't read/parse the job queue serial file")
+
+  except:
+    queue_lock.Close()
+    raise
+
+  return queue_lock