root / lib / uidpool.py @ 1d39e245
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# Copyright (C) 2010 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""User-id pool related functions.
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The user-id pool is cluster-wide configuration option.
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It is stored as a list of user-id ranges.
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This module contains functions used for manipulating the
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user-id pool parameter and for requesting/returning user-ids
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from the pool.
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"""
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import errno |
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import logging |
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import os |
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import random |
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from ganeti import errors |
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from ganeti import constants |
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from ganeti import compat |
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from ganeti import utils |
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def ParseUidPool(value, separator=None): |
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"""Parse a user-id pool definition.
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@param value: string representation of the user-id pool.
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The accepted input format is a list of integer ranges.
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The boundaries are inclusive.
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Example: '1000-5000,8000,9000-9010'.
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@param separator: the separator character between the uids/uid-ranges.
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Defaults to a comma.
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@return: a list of integer pairs (lower, higher range boundaries)
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"""
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if separator is None: |
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separator = ","
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ranges = [] |
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for range_def in value.split(separator): |
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if not range_def: |
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# Skip empty strings
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continue
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boundaries = range_def.split("-")
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n_elements = len(boundaries)
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if n_elements > 2: |
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raise errors.OpPrereqError(
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"Invalid user-id range definition. Only one hyphen allowed: %s"
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% boundaries) |
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try:
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lower = int(boundaries[0]) |
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except (ValueError, TypeError), err: |
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raise errors.OpPrereqError("Invalid user-id value for lower boundary of" |
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" user-id range: %s"
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% str(err), errors.ECODE_INVAL)
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try:
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higher = int(boundaries[n_elements - 1]) |
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except (ValueError, TypeError), err: |
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raise errors.OpPrereqError("Invalid user-id value for higher boundary of" |
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" user-id range: %s"
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% str(err), errors.ECODE_INVAL)
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ranges.append((lower, higher)) |
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ranges.sort() |
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return ranges
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def AddToUidPool(uid_pool, add_uids): |
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"""Add a list of user-ids/user-id ranges to a user-id pool.
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@param uid_pool: a user-id pool (list of integer tuples)
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@param add_uids: user-id ranges to be added to the pool
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(list of integer tuples)
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"""
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for uid_range in add_uids: |
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if uid_range not in uid_pool: |
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uid_pool.append(uid_range) |
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uid_pool.sort() |
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def RemoveFromUidPool(uid_pool, remove_uids): |
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"""Remove a list of user-ids/user-id ranges from a user-id pool.
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@param uid_pool: a user-id pool (list of integer tuples)
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@param remove_uids: user-id ranges to be removed from the pool
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(list of integer tuples)
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"""
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for uid_range in remove_uids: |
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if uid_range not in uid_pool: |
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raise errors.OpPrereqError(
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"User-id range to be removed is not found in the current"
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" user-id pool: %s" % uid_range, errors.ECODE_INVAL)
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uid_pool.remove(uid_range) |
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def _FormatUidRange(lower, higher, roman=False): |
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"""Convert a user-id range definition into a string.
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"""
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if lower == higher:
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return str(compat.TryToRoman(lower, convert=roman)) |
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return "%s-%s" % (compat.TryToRoman(lower, convert=roman), |
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compat.TryToRoman(higher, convert=roman)) |
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def FormatUidPool(uid_pool, separator=None, roman=False): |
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"""Convert the internal representation of the user-id pool into a string.
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The output format is also accepted by ParseUidPool()
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@param uid_pool: a list of integer pairs representing UID ranges
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@param separator: the separator character between the uids/uid-ranges.
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Defaults to ", ".
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@return: a string with the formatted results
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"""
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if separator is None: |
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separator = ", "
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return separator.join([_FormatUidRange(lower, higher, roman=roman)
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for lower, higher in uid_pool]) |
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def CheckUidPool(uid_pool): |
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"""Sanity check user-id pool range definition values.
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@param uid_pool: a list of integer pairs (lower, higher range boundaries)
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"""
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for lower, higher in uid_pool: |
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if lower > higher:
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raise errors.OpPrereqError(
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"Lower user-id range boundary value (%s)"
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" is larger than higher boundary value (%s)" %
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(lower, higher), errors.ECODE_INVAL) |
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if lower < constants.UIDPOOL_UID_MIN:
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raise errors.OpPrereqError(
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"Lower user-id range boundary value (%s)"
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" is smaller than UIDPOOL_UID_MIN (%s)." %
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(lower, constants.UIDPOOL_UID_MIN), |
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errors.ECODE_INVAL) |
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if higher > constants.UIDPOOL_UID_MAX:
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raise errors.OpPrereqError(
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"Higher user-id boundary value (%s)"
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" is larger than UIDPOOL_UID_MAX (%s)." %
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(higher, constants.UIDPOOL_UID_MAX), |
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errors.ECODE_INVAL) |
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def ExpandUidPool(uid_pool): |
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"""Expands a uid-pool definition to a list of uids.
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@param uid_pool: a list of integer pairs (lower, higher range boundaries)
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@return: a list of integers
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"""
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uids = set()
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for lower, higher in uid_pool: |
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uids.update(range(lower, higher + 1)) |
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return list(uids) |
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def _IsUidUsed(uid): |
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"""Check if there is any process in the system running with the given user-id
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@type uid: integer
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@param uid: the user-id to be checked.
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"""
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pgrep_command = [constants.PGREP, "-u", uid]
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result = utils.RunCmd(pgrep_command) |
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if result.exit_code == 0: |
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return True |
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elif result.exit_code == 1: |
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return False |
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else:
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raise errors.CommandError("Running pgrep failed. exit code: %s" |
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% result.exit_code) |
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class LockedUid(object): |
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"""Class representing a locked user-id in the uid-pool.
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This binds together a userid and a lock.
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"""
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def __init__(self, uid, lock): |
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"""Constructor
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@param uid: a user-id
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@param lock: a utils.FileLock object
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"""
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self._uid = uid
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self._lock = lock
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def Unlock(self): |
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# Release the exclusive lock and close the filedescriptor
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self._lock.Close()
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def GetUid(self): |
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return self._uid |
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def AsStr(self): |
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return "%s" % self._uid |
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def RequestUnusedUid(all_uids): |
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"""Tries to find an unused uid from the uid-pool, locks it and returns it.
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Usage pattern
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=============
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1. When starting a process::
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from ganeti import ssconf
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from ganeti import uidpool
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# Get list of all user-ids in the uid-pool from ssconf
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ss = ssconf.SimpleStore()
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uid_pool = uidpool.ParseUidPool(ss.GetUidPool(), separator="\\n")
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all_uids = set(uidpool.ExpandUidPool(uid_pool))
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uid = uidpool.RequestUnusedUid(all_uids)
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try:
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<start a process with the UID>
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# Once the process is started, we can release the file lock
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uid.Unlock()
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except ..., err:
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# Return the UID to the pool
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uidpool.ReleaseUid(uid)
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2. Stopping a process::
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from ganeti import uidpool
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uid = <get the UID the process is running under>
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<stop the process>
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uidpool.ReleaseUid(uid)
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@type all_uids: set of integers
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@param all_uids: a set containing all the user-ids in the user-id pool
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@return: a LockedUid object representing the unused uid. It's the caller's
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responsibility to unlock the uid once an instance is started with
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this uid.
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"""
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# Create the lock dir if it's not yet present
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try:
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utils.EnsureDirs([(constants.UIDPOOL_LOCKDIR, 0755)])
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except errors.GenericError, err:
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raise errors.LockError("Failed to create user-id pool lock dir: %s" % err) |
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# Get list of currently used uids from the filesystem
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try:
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taken_uids = set()
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for taken_uid in os.listdir(constants.UIDPOOL_LOCKDIR): |
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try:
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taken_uid = int(taken_uid)
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except ValueError, err: |
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# Skip directory entries that can't be converted into an integer
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continue
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taken_uids.add(taken_uid) |
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except OSError, err: |
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raise errors.LockError("Failed to get list of used user-ids: %s" % err) |
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# Filter out spurious entries from the directory listing
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taken_uids = all_uids.intersection(taken_uids) |
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# Remove the list of used uids from the list of all uids
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unused_uids = list(all_uids - taken_uids)
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if not unused_uids: |
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logging.info("All user-ids in the uid-pool are marked 'taken'")
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# Randomize the order of the unused user-id list
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random.shuffle(unused_uids) |
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# Randomize the order of the unused user-id list
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taken_uids = list(taken_uids)
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random.shuffle(taken_uids) |
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for uid in (unused_uids + taken_uids): |
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try:
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# Create the lock file
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# Note: we don't care if it exists. Only the fact that we can
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# (or can't) lock it later is what matters.
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uid_path = utils.PathJoin(constants.UIDPOOL_LOCKDIR, str(uid))
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lock = utils.FileLock.Open(uid_path) |
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except OSError, err: |
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raise errors.LockError("Failed to create lockfile for user-id %s: %s" |
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% (uid, err)) |
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try:
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# Try acquiring an exclusive lock on the lock file
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lock.Exclusive() |
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# Check if there is any process running with this user-id
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if _IsUidUsed(uid):
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logging.debug("There is already a process running under"
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" user-id %s", uid)
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lock.Unlock() |
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continue
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return LockedUid(uid, lock)
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except IOError, err: |
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if err.errno == errno.EAGAIN:
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# The file is already locked, let's skip it and try another unused uid
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logging.debug("Lockfile for user-id is already locked %s: %s", uid, err)
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continue
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except errors.LockError, err:
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# There was an unexpected error while trying to lock the file
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logging.error("Failed to lock the lockfile for user-id %s: %s", uid, err)
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raise
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raise errors.LockError("Failed to find an unused user-id") |
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def ReleaseUid(uid): |
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"""This should be called when the given user-id is no longer in use.
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@type uid: LockedUid or integer
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@param uid: the uid to release back to the pool
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"""
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if isinstance(uid, LockedUid): |
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# Make sure we release the exclusive lock, if there is any
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uid.Unlock() |
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uid_filename = uid.AsStr() |
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else:
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uid_filename = str(uid)
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try:
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uid_path = utils.PathJoin(constants.UIDPOOL_LOCKDIR, uid_filename) |
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os.remove(uid_path) |
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except OSError, err: |
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raise errors.LockError("Failed to remove user-id lockfile" |
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" for user-id %s: %s" % (uid_filename, err))
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def ExecWithUnusedUid(fn, all_uids, *args, **kwargs): |
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"""Execute a callable and provide an unused user-id in its kwargs.
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This wrapper function provides a simple way to handle the requesting,
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unlocking and releasing a user-id.
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"fn" is called by passing a "uid" keyword argument that
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contains an unused user-id (as an integer) selected from the set of user-ids
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passed in all_uids.
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If there is an error while executing "fn", the user-id is returned
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to the pool.
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@param fn: a callable that accepts a keyword argument called "uid"
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@type all_uids: a set of integers
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@param all_uids: a set containing all user-ids in the user-id pool
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"""
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uid = RequestUnusedUid(all_uids) |
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kwargs["uid"] = uid.GetUid()
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try:
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return_value = fn(*args, **kwargs) |
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except:
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# The failure of "callabe" means that starting a process with the uid
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# failed, so let's put the uid back into the pool.
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ReleaseUid(uid) |
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raise
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uid.Unlock() |
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return return_value
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