Source Code for Module ganeti.jstore

  1  # 
  2  # 
  3   
  4  # Copyright (C) 2006, 2007 Google Inc. 
  5  # 
  6  # This program is free software; you can redistribute it and/or modify 
  7  # it under the terms of the GNU General Public License as published by 
  8  # the Free Software Foundation; either version 2 of the License, or 
  9  # (at your option) any later version. 
 10  # 
 11  # This program is distributed in the hope that it will be useful, but 
 12  # WITHOUT ANY WARRANTY; without even the implied warranty of 
 13  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
 14  # General Public License for more details. 
 15  # 
 16  # You should have received a copy of the GNU General Public License 
 17  # along with this program; if not, write to the Free Software 
 18  # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 
 19  # 02110-1301, USA. 
 20   
 21   
 22  """Module implementing the job queue handling.""" 
 23   
 24  import errno 
 25   
 26  from ganeti import constants 
 27  from ganeti import errors 
 28  from ganeti import runtime 
 29  from ganeti import utils 
 30   
 31   
 32 -def _ReadNumericFile(file_name): 
 33    """Reads a file containing a number. 
 34   
 35    @rtype: None or int 
 36    @return: None if file is not found, otherwise number 
 37   
 38    """ 
 39    try: 
 40      return int(utils.ReadFile(file_name)) 
 41    except EnvironmentError, err: 
 42      if err.errno in (errno.ENOENT, ): 
 43        return None 
 44      raise 
 45   
 46   
 47 -def ReadSerial(): 
 48    """Read the serial file. 
 49   
 50    The queue should be locked while this function is called. 
 51   
 52    """ 
 53    return _ReadNumericFile(constants.JOB_QUEUE_SERIAL_FILE) 
 54   
 55   
 56 -def ReadVersion(): 
 57    """Read the queue version. 
 58   
 59    The queue should be locked while this function is called. 
 60   
 61    """ 
 62    return _ReadNumericFile(constants.JOB_QUEUE_VERSION_FILE) 
 63   
 64   
 65 -def InitAndVerifyQueue(must_lock): 
 66    """Open and lock job queue. 
 67   
 68    If necessary, the queue is automatically initialized. 
 69   
 70    @type must_lock: bool 
 71    @param must_lock: Whether an exclusive lock must be held. 
 72    @rtype: utils.FileLock 
 73    @return: Lock object for the queue. This can be used to change the 
 74             locking mode. 
 75   
 76    """ 
 77    getents = runtime.GetEnts() 
 78   
 79    # Lock queue 
 80    queue_lock = utils.FileLock.Open(constants.JOB_QUEUE_LOCK_FILE) 
 81    try: 
 82      # The queue needs to be locked in exclusive mode to write to the serial and 
 83      # version files. 
 84      if must_lock: 
 85        queue_lock.Exclusive(blocking=True) 
 86        holding_lock = True 
 87      else: 
 88        try: 
 89          queue_lock.Exclusive(blocking=False) 
 90          holding_lock = True 
 91        except errors.LockError: 
 92          # Ignore errors and assume the process keeping the lock checked 
 93          # everything. 
 94          holding_lock = False 
 95   
 96      if holding_lock: 
 97        # Verify version 
 98        version = ReadVersion() 
 99        if version is None: 
100          # Write new version file 
101          utils.WriteFile(constants.JOB_QUEUE_VERSION_FILE, 
102                          uid=getents.masterd_uid, gid=getents.masterd_gid, 
103                          data="%s\n" % constants.JOB_QUEUE_VERSION) 
104   
105          # Read again 
106          version = ReadVersion() 
107   
108        if version != constants.JOB_QUEUE_VERSION: 
109          raise errors.JobQueueError("Found job queue version %s, expected %s", 
110                                     version, constants.JOB_QUEUE_VERSION) 
111   
112        serial = ReadSerial() 
113        if serial is None: 
114          # Write new serial file 
115          utils.WriteFile(constants.JOB_QUEUE_SERIAL_FILE, 
116                          uid=getents.masterd_uid, gid=getents.masterd_gid, 
117                          data="%s\n" % 0) 
118   
119          # Read again 
120          serial = ReadSerial() 
121   
122        if serial is None: 
123          # There must be a serious problem 
124          raise errors.JobQueueError("Can't read/parse the job queue" 
125                                     " serial file") 
126   
127        if not must_lock: 
128          # There's no need for more error handling. Closing the lock 
129          # file below in case of an error will unlock it anyway. 
130          queue_lock.Unlock() 
131   
132    except: 
133      queue_lock.Close() 
134      raise 
135   
136    return queue_lock 
137