Synnefo » snf-ganeti

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#

# Copyright (C) 2010 Google Inc.

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# 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

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# This program is distributed in the hope that it will be useful, but

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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

# General Public License for more details.

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# 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.

"""User-id pool related functions.

The user-id pool is cluster-wide configuration option.

It is stored as a list of user-id ranges.

This module contains functions used for manipulating the

user-id pool parameter and for requesting/returning user-ids

from the pool.

"""

import errno

import logging

import os

import random

from ganeti import errors

from ganeti import constants

from ganeti import utils

def ParseUidPool(value, separator=None):

  """Parse a user-id pool definition.

  @param value: string representation of the user-id pool.

                The accepted input format is a list of integer ranges.

                The boundaries are inclusive.

                Example: '1000-5000,8000,9000-9010'.

  @param separator: the separator character between the uids/uid-ranges.

                    Defaults to a comma.

  @return: a list of integer pairs (lower, higher range boundaries)

  """

  if separator is None:

    separator = ","

  ranges = []

  for range_def in value.split(separator):

    if not range_def:

      # Skip empty strings

      continue

    boundaries = range_def.split("-")

    n_elements = len(boundaries)

    if n_elements > 2:

      raise errors.OpPrereqError(

          "Invalid user-id range definition. Only one hyphen allowed: %s"

          % boundaries)

    try:

      lower = int(boundaries[0])

    except (ValueError, TypeError), err:

      raise errors.OpPrereqError("Invalid user-id value for lower boundary of"

                                 " user-id range: %s"

                                 % str(err), errors.ECODE_INVAL)

    try:

      higher = int(boundaries[n_elements - 1])

    except (ValueError, TypeError), err:

      raise errors.OpPrereqError("Invalid user-id value for higher boundary of"

                                 " user-id range: %s"

                                 % str(err), errors.ECODE_INVAL)

    ranges.append((lower, higher))

  ranges.sort()

  return ranges

def AddToUidPool(uid_pool, add_uids):

  """Add a list of user-ids/user-id ranges to a user-id pool.

  @param uid_pool: a user-id pool (list of integer tuples)

  @param add_uids: user-id ranges to be added to the pool

                   (list of integer tuples)

  """

  for uid_range in add_uids:

    if uid_range not in uid_pool:

      uid_pool.append(uid_range)

  uid_pool.sort()

def RemoveFromUidPool(uid_pool, remove_uids):

  """Remove a list of user-ids/user-id ranges from a user-id pool.

  @param uid_pool: a user-id pool (list of integer tuples)

  @param remove_uids: user-id ranges to be removed from the pool

                      (list of integer tuples)

  """

  for uid_range in remove_uids:

    if uid_range not in uid_pool:

      raise errors.OpPrereqError(

          "User-id range to be removed is not found in the current"

          " user-id pool: %s" % uid_range, errors.ECODE_INVAL)

    uid_pool.remove(uid_range)

def _FormatUidRange(lower, higher):

  """Convert a user-id range definition into a string.

  """

  if lower == higher:

    return str(lower)

  return "%s-%s" % (lower, higher)

def FormatUidPool(uid_pool, separator=None):

  """Convert the internal representation of the user-id pool into a string.

  The output format is also accepted by ParseUidPool()

  @param uid_pool: a list of integer pairs representing UID ranges

  @param separator: the separator character between the uids/uid-ranges.

                    Defaults to ", ".

  @return: a string with the formatted results

  """

  if separator is None:

    separator = ", "

  return separator.join([_FormatUidRange(lower, higher)

                         for lower, higher in uid_pool])

def CheckUidPool(uid_pool):

  """Sanity check user-id pool range definition values.

  @param uid_pool: a list of integer pairs (lower, higher range boundaries)

  """

  for lower, higher in uid_pool:

    if lower > higher:

      raise errors.OpPrereqError(

          "Lower user-id range boundary value (%s)"

          " is larger than higher boundary value (%s)" %

          (lower, higher), errors.ECODE_INVAL)

    if lower < constants.UIDPOOL_UID_MIN:

      raise errors.OpPrereqError(

          "Lower user-id range boundary value (%s)"

          " is smaller than UIDPOOL_UID_MIN (%s)." %

          (lower, constants.UIDPOOL_UID_MIN),

          errors.ECODE_INVAL)

    if higher > constants.UIDPOOL_UID_MAX:

      raise errors.OpPrereqError(

          "Higher user-id boundary value (%s)"

          " is larger than UIDPOOL_UID_MAX (%s)." %

          (higher, constants.UIDPOOL_UID_MAX),

          errors.ECODE_INVAL)

def ExpandUidPool(uid_pool):

  """Expands a uid-pool definition to a list of uids.

  @param uid_pool: a list of integer pairs (lower, higher range boundaries)

  @return: a list of integers

  """

  uids = set()

  for lower, higher in uid_pool:

    uids.update(range(lower, higher + 1))

  return list(uids)

def _IsUidUsed(uid):

  """Check if there is any process in the system running with the given user-id

  """

  pgrep_command = [constants.PGREP, "-u", uid]

  result = utils.RunCmd(pgrep_command)

  if result.exit_code == 0:

    return True

  elif result.exit_code == 1:

    return False

  else:

    raise errors.CommandError("Running pgrep failed. exit code: %s"

                              % result.exit_code)

class LockedUid(object):

  """Class representing a locked user-id in the uid-pool.

  This binds together a userid and a lock.

  """

  def __init__(self, uid, lock):

    """Constructor

    @param uid: a user-id

    @param lock: a utils.FileLock object

    """

    self._uid = uid

    self._lock = lock

  def Unlock(self):

    # Release the exclusive lock and close the filedescriptor

    self._lock.Close()

  def __str__(self):

    return "%s" % self._uid

def RequestUnusedUid(all_uids):

  """Tries to find an unused uid from the uid-pool, locks it and returns it.

  Usage pattern

  =============

  1. When starting a process::

      from ganeti import ssconf

      from ganeti import uidpool

      # Get list of all user-ids in the uid-pool from ssconf

      ss = ssconf.SimpleStore()

      uid_pool = uidpool.ParseUidPool(ss.GetUidPool(), separator="\\n")

      all_uids = set(uidpool.ExpandUidPool(uid_pool))

      uid = uidpool.RequestUnusedUid(all_uids)

      try:

        <start a process with the UID>

        # Once the process is started, we can release the file lock

        uid.Unlock()

      except ..., err:

        # Return the UID to the pool

        uidpool.ReleaseUid(uid)

  2. Stopping a process::

      from ganeti import uidpool

      uid = <get the UID the process is running under>

      <stop the process>

      uidpool.ReleaseUid(uid)

  @param all_uids: a set containing all the user-ids in the user-id pool

  @return: a LockedUid object representing the unused uid. It's the caller's

           responsibility to unlock the uid once an instance is started with

           this uid.

  """

  # Create the lock dir if it's not yet present

  try:

    utils.EnsureDirs([(constants.UIDPOOL_LOCKDIR, 0755)])

  except errors.GenericError, err:

    raise errors.LockError("Failed to create user-id pool lock dir: %s" % err)

  # Get list of currently used uids from the filesystem

  try:

    taken_uids = set(os.listdir(constants.UIDPOOL_LOCKDIR))

    # Filter out spurious entries from the directory listing

    taken_uids = all_uids.intersection(taken_uids)

  except OSError, err:

    raise errors.LockError("Failed to get list of used user-ids: %s" % err)

  # Remove the list of used uids from the list of all uids

  unused_uids = list(all_uids - taken_uids)

  if not unused_uids:

    logging.info("All user-ids in the uid-pool are marked 'taken'")

  # Randomize the order of the unused user-id list

  random.shuffle(unused_uids)

  # Randomize the order of the unused user-id list

  taken_uids = list(taken_uids)

  random.shuffle(taken_uids)

  for uid in (unused_uids + taken_uids):

    try:

      # Create the lock file

      # Note: we don't care if it exists. Only the fact that we can

      # (or can't) lock it later is what matters.

      uid_path = utils.PathJoin(constants.UIDPOOL_LOCKDIR, str(uid))

      lock = utils.FileLock.Open(uid_path)

    except OSError, err:

      raise errors.LockError("Failed to create lockfile for user-id %s: %s"

                             % (uid, err))

    try:

      # Try acquiring an exclusive lock on the lock file

      lock.Exclusive()

      # Check if there is any process running with this user-id

      if _IsUidUsed(uid):

        logging.debug("There is already a process running under"

                      " user-id %s", uid)

        lock.Unlock()

        continue

      return LockedUid(uid, lock)

    except IOError, err:

      if err.errno == errno.EAGAIN:

        # The file is already locked, let's skip it and try another unused uid

        logging.debug("Lockfile for user-id is already locked %s: %s", uid, err)

        continue

    except errors.LockError, err:

      # There was an unexpected error while trying to lock the file

      logging.error("Failed to lock the lockfile for user-id %s: %s", uid, err)

      raise

  raise errors.LockError("Failed to find an unused user-id")

def ReleaseUid(uid):

  """This should be called when the given user-id is no longer in use.

  """

  # Make sure we release the exclusive lock, if there is any

  uid.Unlock()

  try:

    uid_path = utils.PathJoin(constants.UIDPOOL_LOCKDIR, str(uid))

    os.remove(uid_path)

  except OSError, err:

    raise errors.LockError("Failed to remove user-id lockfile"

                           " for user-id %s: %s" % (uid, err))

def ExecWithUnusedUid(fn, all_uids, *args, **kwargs):

  """Execute a callable and provide an unused user-id in its kwargs.

  This wrapper function provides a simple way to handle the requesting,

  unlocking and releasing a user-id.

  "fn" is called by passing a "uid" keyword argument that

  contains an unused user-id (as a string) selected from the set of user-ids

  passed in all_uids.

  If there is an error while executing "fn", the user-id is returned

  to the pool.

  @param fn: a callable

  @param all_uids: a set containing all user-ids in the user-id pool

  """

  uid = RequestUnusedUid(all_uids)

  kwargs["uid"] = str(uid)

  try:

    return_value = fn(*args, **kwargs)

  except:

    # The failure of "callabe" means that starting a process with the uid

    # failed, so let's put the uid back into the pool.

    ReleaseUid(uid)

    raise

  uid.Unlock()

  return return_value