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+      #
+      #
       # 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.
       """Block device abstraction"""
       import re
       import time
       import errno
       import pyparsing as pyp
       import os
       import logging
       from ganeti import utils
       from ganeti import errors
       from ganeti import constants
       class BlockDev(object):
         """Block device abstract class.
         A block device can be in the following states:
           - not existing on the system, and by `Create()` it goes into:
           - existing but not setup/not active, and by `Assemble()` goes into:
           - active read-write and by `Open()` it goes into
           - online (=used, or ready for use)
         A device can also be online but read-only, however we are not using
         the readonly state (LV has it, if needed in the future) and we are
         usually looking at this like at a stack, so it's easier to
         conceptualise the transition from not-existing to online and back
         like a linear one.
         The many different states of the device are due to the fact that we
         need to cover many device types:
           - logical volumes are created, lvchange -a y $lv, and used
           - drbd devices are attached to a local disk/remote peer and made primary
         A block device is identified by three items:
           - the /dev path of the device (dynamic)
           - a unique ID of the device (static)
           - it's major/minor pair (dynamic)
         Not all devices implement both the first two as distinct items. LVM
         logical volumes have their unique ID (the pair volume group, logical
         volume name) in a 1-to-1 relation to the dev path. For DRBD devices,
         the /dev path is again dynamic and the unique id is the pair (host1,
         dev1), (host2, dev2).
         You can get to a device in two ways:
           - creating the (real) device, which returns you
             an attached instance (lvcreate)
           - attaching of a python instance to an existing (real) device
         The second point, the attachement to a device, is different
         depending on whether the device is assembled or not. At init() time,
         we search for a device with the same unique_id as us. If found,
         good. It also means that the device is already assembled. If not,
         after assembly we'll have our correct major/minor.
         """
         def __init__(self, unique_id, children):
           self._children = children
           self.dev_path = None
           self.unique_id = unique_id
           self.major = None
           self.minor = None
           self.attached = False
         def Assemble(self):
           """Assemble the device from its components.
           Implementations of this method by child classes must ensure that:
             - after the device has been assembled, it knows its major/minor
               numbers; this allows other devices (usually parents) to probe
               correctly for their children
             - calling this method on an existing, in-use device is safe
             - if the device is already configured (and in an OK state),
               this method is idempotent
           """
           return True
         def Attach(self):
           """Find a device which matches our config and attach to it.
           """
           raise NotImplementedError
         def Close(self):
           """Notifies that the device will no longer be used for I/O.
           """
           raise NotImplementedError
         @classmethod
         def Create(cls, unique_id, children, size):
           """Create the device.
           If the device cannot be created, it will return None
           instead. Error messages go to the logging system.
           Note that for some devices, the unique_id is used, and for other,
           the children. The idea is that these two, taken together, are
           enough for both creation and assembly (later).
           """
           raise NotImplementedError
         def Remove(self):
           """Remove this device.
           This makes sense only for some of the device types: LV and file
           storeage. Also note that if the device can't attach, the removal
           can't be completed.
           """
           raise NotImplementedError
         def Rename(self, new_id):
           """Rename this device.
           This may or may not make sense for a given device type.
           """
           raise NotImplementedError
         def Open(self, force=False):
           """Make the device ready for use.
           This makes the device ready for I/O. For now, just the DRBD
           devices need this.
           The force parameter signifies that if the device has any kind of
           --force thing, it should be used, we know what we are doing.
           """
           raise NotImplementedError
         def Shutdown(self):
           """Shut down the device, freeing its children.
           This undoes the `Assemble()` work, except for the child
           assembling; as such, the children on the device are still
           assembled after this call.
           """
           raise NotImplementedError
         def SetSyncSpeed(self, speed):
           """Adjust the sync speed of the mirror.
           In case this is not a mirroring device, this is no-op.
           """
           result = True
           if self._children:
             for child in self._children:
               result = result and child.SetSyncSpeed(speed)
           return result
         def GetSyncStatus(self):
           """Returns the sync status of the device.
           If this device is a mirroring device, this function returns the
           status of the mirror.
           If sync_percent is None, it means the device is not syncing.
           If estimated_time is None, it means we can't estimate
           the time needed, otherwise it's the time left in seconds.
           If is_degraded is True, it means the device is missing
           redundancy. This is usually a sign that something went wrong in
           the device setup, if sync_percent is None.
           The ldisk parameter represents the degradation of the local
           data. This is only valid for some devices, the rest will always
           return False (not degraded).
           @rtype: tuple
           @return: (sync_percent, estimated_time, is_degraded, ldisk)
           """
           return None, None, False, False
         def CombinedSyncStatus(self):
           """Calculate the mirror status recursively for our children.
           The return value is the same as for `GetSyncStatus()` except the
           minimum percent and maximum time are calculated across our
           children.
           """
           min_percent, max_time, is_degraded, ldisk = self.GetSyncStatus()
           if self._children:
             for child in self._children:
               c_percent, c_time, c_degraded, c_ldisk = child.GetSyncStatus()
               if min_percent is None:
                 min_percent = c_percent
               elif c_percent is not None:
                 min_percent = min(min_percent, c_percent)
               if max_time is None:
                 max_time = c_time
               elif c_time is not None:
                 max_time = max(max_time, c_time)
               is_degraded = is_degraded or c_degraded
               ldisk = ldisk or c_ldisk
           return min_percent, max_time, is_degraded, ldisk
         def SetInfo(self, text):
           """Update metadata with info text.
           Only supported for some device types.
           """
           for child in self._children:
             child.SetInfo(text)
         def Grow(self, amount):
           """Grow the block device.
           @param amount: the amount (in mebibytes) to grow with
           """
           raise NotImplementedError
         def __repr__(self):
           return ("<%s: unique_id: %s, children: %s, %s:%s, %s>" %
                   (self.__class__, self.unique_id, self._children,
                    self.major, self.minor, self.dev_path))
       class LogicalVolume(BlockDev):
         """Logical Volume block device.
         """
         def __init__(self, unique_id, children):
           """Attaches to a LV device.
           The unique_id is a tuple (vg_name, lv_name)
           """
           super(LogicalVolume, self).__init__(unique_id, children)
           if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
             raise ValueError("Invalid configuration data %s" % str(unique_id))
           self._vg_name, self._lv_name = unique_id
           self.dev_path = "/dev/%s/%s" % (self._vg_name, self._lv_name)
           self._degraded = True
           self.major = self.minor = None
           self.Attach()
         @classmethod
         def Create(cls, unique_id, children, size):
           """Create a new logical volume.
           """
           if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
             raise ValueError("Invalid configuration data %s" % str(unique_id))
           vg_name, lv_name = unique_id
           pvs_info = cls.GetPVInfo(vg_name)
           if not pvs_info:
             raise errors.BlockDeviceError("Can't compute PV info for vg %s" %
                                           vg_name)
           pvs_info.sort()
           pvs_info.reverse()
           pvlist = [ pv[1] for pv in pvs_info ]
           free_size = sum([ pv[0] for pv in pvs_info ])
           # The size constraint should have been checked from the master before
           # calling the create function.
           if free_size < size:
             raise errors.BlockDeviceError("Not enough free space: required %s,"
                                           " available %s" % (size, free_size))
           result = utils.RunCmd(["lvcreate", "-L%dm" % size, "-n%s" % lv_name,
                                  vg_name] + pvlist)
           if result.failed:
             raise errors.BlockDeviceError("%s - %s" % (result.fail_reason,
                                                       result.output))
           return LogicalVolume(unique_id, children)
         @staticmethod
         def GetPVInfo(vg_name):
           """Get the free space info for PVs in a volume group.
           @param vg_name: the volume group name
           @rtype: list
           @return: list of tuples (free_space, name) with free_space in mebibytes
           """
           command = ["pvs", "--noheadings", "--nosuffix", "--units=m",
                      "-opv_name,vg_name,pv_free,pv_attr", "--unbuffered",
                      "--separator=:"]
           result = utils.RunCmd(command)
           if result.failed:
             logging.error("Can't get the PV information: %s - %s",
                           result.fail_reason, result.output)
             return None
           data = []
           for line in result.stdout.splitlines():
             fields = line.strip().split(':')
             if len(fields) != 4:
               logging.error("Can't parse pvs output: line '%s'", line)
               return None
             # skip over pvs from another vg or ones which are not allocatable
             if fields[1] != vg_name or fields[3][0] != 'a':
               continue
             data.append((float(fields[2]), fields[0]))
           return data
         def Remove(self):
           """Remove this logical volume.
           """
           if not self.minor and not self.Attach():
             # the LV does not exist
             return True
           result = utils.RunCmd(["lvremove", "-f", "%s/%s" %
                                  (self._vg_name, self._lv_name)])
           if result.failed:
             logging.error("Can't lvremove: %s - %s",
                           result.fail_reason, result.output)
           return not result.failed
         def Rename(self, new_id):
           """Rename this logical volume.
           """
           if not isinstance(new_id, (tuple, list)) or len(new_id) != 2:
             raise errors.ProgrammerError("Invalid new logical id '%s'" % new_id)
           new_vg, new_name = new_id
           if new_vg != self._vg_name:
             raise errors.ProgrammerError("Can't move a logical volume across"
                                          " volume groups (from %s to to %s)" %
                                          (self._vg_name, new_vg))
           result = utils.RunCmd(["lvrename", new_vg, self._lv_name, new_name])
           if result.failed:
             raise errors.BlockDeviceError("Failed to rename the logical volume: %s" %
                                           result.output)
           self._lv_name = new_name
           self.dev_path = "/dev/%s/%s" % (self._vg_name, self._lv_name)
         def Attach(self):
           """Attach to an existing LV.
           This method will try to see if an existing and active LV exists
           which matches our name. If so, its major/minor will be
           recorded.
           """
           self.attached = False
           result = utils.RunCmd(["lvs", "--noheadings", "--separator=,",
                                  "-olv_attr,lv_kernel_major,lv_kernel_minor",
                                  self.dev_path])
           if result.failed:
             logging.error("Can't find LV %s: %s, %s",
                           self.dev_path, result.fail_reason, result.output)
             return False
           out = result.stdout.strip().rstrip(',')
           out = out.split(",")
           if len(out) != 3:
             logging.error("Can't parse LVS output, len(%s) != 3", str(out))
             return False
           status, major, minor = out[:3]
           if len(status) != 6:
             logging.error("lvs lv_attr is not 6 characters (%s)", status)
             return False
           try:
             major = int(major)
             minor = int(minor)
           except ValueError, err:
             logging.error("lvs major/minor cannot be parsed: %s", str(err))
           self.major = major
           self.minor = minor
           self._degraded = status[0] == 'v' # virtual volume, i.e. doesn't backing
                                             # storage
           self.attached = True
           return True
         def Assemble(self):
           """Assemble the device.
           We alway run `lvchange -ay` on the LV to ensure it's active before
           use, as there were cases when xenvg was not active after boot
           (also possibly after disk issues).
           """
           result = utils.RunCmd(["lvchange", "-ay", self.dev_path])
           if result.failed:
             logging.error("Can't activate lv %s: %s", self.dev_path, result.output)
             return False
           return self.Attach()
         def Shutdown(self):
           """Shutdown the device.
           This is a no-op for the LV device type, as we don't deactivate the
           volumes on shutdown.
           """
           return True
         def GetSyncStatus(self):
           """Returns the sync status of the device.
           If this device is a mirroring device, this function returns the
           status of the mirror.
           For logical volumes, sync_percent and estimated_time are always
           None (no recovery in progress, as we don't handle the mirrored LV
           case). The is_degraded parameter is the inverse of the ldisk
           parameter.
           For the ldisk parameter, we check if the logical volume has the
           'virtual' type, which means it's not backed by existing storage
           anymore (read from it return I/O error). This happens after a
           physical disk failure and subsequent 'vgreduce --removemissing' on
           the volume group.
           The status was already read in Attach, so we just return it.
           @rtype: tuple
           @return: (sync_percent, estimated_time, is_degraded, ldisk)
           """
           return None, None, self._degraded, self._degraded
         def Open(self, force=False):
           """Make the device ready for I/O.
           This is a no-op for the LV device type.
           """
           pass
         def Close(self):
           """Notifies that the device will no longer be used for I/O.
           This is a no-op for the LV device type.
           """
           pass
         def Snapshot(self, size):
           """Create a snapshot copy of an lvm block device.
           """
           snap_name = self._lv_name + ".snap"
           # remove existing snapshot if found
           snap = LogicalVolume((self._vg_name, snap_name), None)
           snap.Remove()
           pvs_info = self.GetPVInfo(self._vg_name)
           if not pvs_info:
             raise errors.BlockDeviceError("Can't compute PV info for vg %s" %
                                           self._vg_name)
           pvs_info.sort()
           pvs_info.reverse()
           free_size, pv_name = pvs_info[0]
           if free_size < size:
             raise errors.BlockDeviceError("Not enough free space: required %s,"
                                           " available %s" % (size, free_size))
           result = utils.RunCmd(["lvcreate", "-L%dm" % size, "-s",
                                  "-n%s" % snap_name, self.dev_path])
           if result.failed:
             raise errors.BlockDeviceError("command: %s error: %s - %s" %
                                           (result.cmd, result.fail_reason,
                                            result.output))
           return snap_name
         def SetInfo(self, text):
           """Update metadata with info text.
           """
           BlockDev.SetInfo(self, text)
           # Replace invalid characters
           text = re.sub('^[^A-Za-z0-9_+.]', '_', text)
           text = re.sub('[^-A-Za-z0-9_+.]', '_', text)
           # Only up to 128 characters are allowed
           text = text[:128]
           result = utils.RunCmd(["lvchange", "--addtag", text,
                                  self.dev_path])
           if result.failed:
             raise errors.BlockDeviceError("Command: %s error: %s - %s" %
                                           (result.cmd, result.fail_reason,
                                            result.output))
         def Grow(self, amount):
           """Grow the logical volume.
           """
           # we try multiple algorithms since the 'best' ones might not have
           # space available in the right place, but later ones might (since
           # they have less constraints); also note that only recent LVM
           # supports 'cling'
           for alloc_policy in "contiguous", "cling", "normal":
             result = utils.RunCmd(["lvextend", "--alloc", alloc_policy,
                                    "-L", "+%dm" % amount, self.dev_path])
             if not result.failed:
               return
           raise errors.BlockDeviceError("Can't grow LV %s: %s" %
                                         (self.dev_path, result.output))
       class DRBD8Status(object):
         """A DRBD status representation class.
         Note that this doesn't support unconfigured devices (cs:Unconfigured).
         """
         LINE_RE = re.compile(r"\s*[0-9]+:\s*cs:(\S+)\s+st:([^/]+)/(\S+)"
                              "\s+ds:([^/]+)/(\S+)\s+.*$")
         SYNC_RE = re.compile(r"^.*\ssync'ed:\s*([0-9.]+)%.*"
                              "\sfinish: ([0-9]+):([0-9]+):([0-9]+)\s.*$")
         def __init__(self, procline):
           m = self.LINE_RE.match(procline)
           if not m:
             raise errors.BlockDeviceError("Can't parse input data '%s'" % procline)
           self.cstatus = m.group(1)
           self.lrole = m.group(2)
           self.rrole = m.group(3)
           self.ldisk = m.group(4)
           self.rdisk = m.group(5)
           self.is_standalone = self.cstatus == "StandAlone"
           self.is_wfconn = self.cstatus == "WFConnection"
           self.is_connected = self.cstatus == "Connected"
           self.is_primary = self.lrole == "Primary"
           self.is_secondary = self.lrole == "Secondary"
           self.peer_primary = self.rrole == "Primary"
           self.peer_secondary = self.rrole == "Secondary"
           self.both_primary = self.is_primary and self.peer_primary
           self.both_secondary = self.is_secondary and self.peer_secondary
           self.is_diskless = self.ldisk == "Diskless"
           self.is_disk_uptodate = self.ldisk == "UpToDate"
           m = self.SYNC_RE.match(procline)
           if m:
             self.sync_percent = float(m.group(1))
             hours = int(m.group(2))
             minutes = int(m.group(3))
             seconds = int(m.group(4))
             self.est_time = hours * 3600 + minutes * 60 + seconds
           else:
             self.sync_percent = None
             self.est_time = None
           self.is_sync_target = self.peer_sync_source = self.cstatus == "SyncTarget"
           self.peer_sync_target = self.is_sync_source = self.cstatus == "SyncSource"
           self.is_resync = self.is_sync_target or self.is_sync_source
       class BaseDRBD(BlockDev):
         """Base DRBD class.
         This class contains a few bits of common functionality between the
 .7 and 8.x versions of DRBD.
         """
         _VERSION_RE = re.compile(r"^version: (\d+)\.(\d+)\.(\d+)"
                                  r" \(api:(\d+)/proto:(\d+)(?:-(\d+))?\)")
         _DRBD_MAJOR = 147
         _ST_UNCONFIGURED = "Unconfigured"
         _ST_WFCONNECTION = "WFConnection"
         _ST_CONNECTED = "Connected"
         _STATUS_FILE = "/proc/drbd"
         @staticmethod
         def _GetProcData(filename=_STATUS_FILE):
           """Return data from /proc/drbd.
           """
           stat = open(filename, "r")
           try:
             data = stat.read().splitlines()
           finally:
             stat.close()
           if not data:
             raise errors.BlockDeviceError("Can't read any data from %s" % filename)
           return data
         @staticmethod
         def _MassageProcData(data):
           """Transform the output of _GetProdData into a nicer form.
           @return: a dictionary of minor: joined lines from /proc/drbd
               for that minor
           """
           lmatch = re.compile("^ *([0-9]+):.*$")
           results = {}
           old_minor = old_line = None
           for line in data:
             lresult = lmatch.match(line)
             if lresult is not None:
               if old_minor is not None:
                 results[old_minor] = old_line
               old_minor = int(lresult.group(1))
               old_line = line
             else:
               if old_minor is not None:
                 old_line += " " + line.strip()
           # add last line
           if old_minor is not None:
             results[old_minor] = old_line
           return results
         @classmethod
         def _GetVersion(cls):
           """Return the DRBD version.
           This will return a dict with keys:
             - k_major
             - k_minor
             - k_point
             - api
             - proto
             - proto2 (only on drbd > 8.2.X)
           """
           proc_data = cls._GetProcData()
           first_line = proc_data[0].strip()
           version = cls._VERSION_RE.match(first_line)
           if not version:
             raise errors.BlockDeviceError("Can't parse DRBD version from '%s'" %
                                           first_line)
           values = version.groups()
           retval = {'k_major': int(values[0]),
                     'k_minor': int(values[1]),
                     'k_point': int(values[2]),
                     'api': int(values[3]),
                     'proto': int(values[4]),
+                   }
           if values[5] is not None:
             retval['proto2'] = values[5]
           return retval
         @staticmethod
         def _DevPath(minor):
           """Return the path to a drbd device for a given minor.
           """
           return "/dev/drbd%d" % minor
         @classmethod
         def _GetUsedDevs(cls):
           """Compute the list of used DRBD devices.
           """
           data = cls._GetProcData()
           used_devs = {}
           valid_line = re.compile("^ *([0-9]+): cs:([^ ]+).*$")
           for line in data:
             match = valid_line.match(line)
             if not match:
               continue
             minor = int(match.group(1))
             state = match.group(2)
             if state == cls._ST_UNCONFIGURED:
               continue
             used_devs[minor] = state, line
           return used_devs
         def _SetFromMinor(self, minor):
           """Set our parameters based on the given minor.
           This sets our minor variable and our dev_path.
           """
           if minor is None:
             self.minor = self.dev_path = None
             self.attached = False
           else:
             self.minor = minor
             self.dev_path = self._DevPath(minor)
             self.attached = True
         @staticmethod
         def _CheckMetaSize(meta_device):
           """Check if the given meta device looks like a valid one.
           This currently only check the size, which must be around
 MiB.
           """
           result = utils.RunCmd(["blockdev", "--getsize", meta_device])
           if result.failed:
             logging.error("Failed to get device size: %s - %s",
                           result.fail_reason, result.output)
             return False
           try:
             sectors = int(result.stdout)
           except ValueError:
             logging.error("Invalid output from blockdev: '%s'", result.stdout)
             return False
           bytes = sectors * 512
           if bytes < 128 * 1024 * 1024: # less than 128MiB
             logging.error("Meta device too small (%.2fMib)", (bytes / 1024 / 1024))
             return False
           if bytes > (128 + 32) * 1024 * 1024: # account for an extra (big) PE on LVM
             logging.error("Meta device too big (%.2fMiB)", (bytes / 1024 / 1024))
             return False
           return True
         def Rename(self, new_id):
           """Rename a device.
           This is not supported for drbd devices.
           """
           raise errors.ProgrammerError("Can't rename a drbd device")
       class DRBD8(BaseDRBD):
         """DRBD v8.x block device.
         This implements the local host part of the DRBD device, i.e. it
         doesn't do anything to the supposed peer. If you need a fully
         connected DRBD pair, you need to use this class on both hosts.
         The unique_id for the drbd device is the (local_ip, local_port,
         remote_ip, remote_port) tuple, and it must have two children: the
         data device and the meta_device. The meta device is checked for
         valid size and is zeroed on create.
         """
         _MAX_MINORS = 255
         _PARSE_SHOW = None
         # timeout constants
         _NET_RECONFIG_TIMEOUT = 60
         def __init__(self, unique_id, children):
           if children and children.count(None) > 0:
             children = []
           super(DRBD8, self).__init__(unique_id, children)
           self.major = self._DRBD_MAJOR
           version = self._GetVersion()
           if version['k_major'] != 8 :
             raise errors.BlockDeviceError("Mismatch in DRBD kernel version and"
                                           " requested ganeti usage: kernel is"
                                           " %s.%s, ganeti wants 8.x" %
                                           (version['k_major'], version['k_minor']))
           if len(children) not in (0, 2):
             raise ValueError("Invalid configuration data %s" % str(children))
           if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 6:
             raise ValueError("Invalid configuration data %s" % str(unique_id))
           (self._lhost, self._lport,
            self._rhost, self._rport,
            self._aminor, self._secret) = unique_id
           if (self._lhost is not None and self._lhost == self._rhost and
               self._lport == self._rport):
             raise ValueError("Invalid configuration data, same local/remote %s" %
                              (unique_id,))
           self.Attach()
         @classmethod
         def _InitMeta(cls, minor, dev_path):
           """Initialize a meta device.
           This will not work if the given minor is in use.
           """
           result = utils.RunCmd(["drbdmeta", "--force", cls._DevPath(minor),
                                  "v08", dev_path, "0", "create-md"])
           if result.failed:
             raise errors.BlockDeviceError("Can't initialize meta device: %s" %
                                           result.output)
         @classmethod
         def _FindUnusedMinor(cls):
           """Find an unused DRBD device.
           This is specific to 8.x as the minors are allocated dynamically,
           so non-existing numbers up to a max minor count are actually free.
           """
           data = cls._GetProcData()
           unused_line = re.compile("^ *([0-9]+): cs:Unconfigured$")
           used_line = re.compile("^ *([0-9]+): cs:")
           highest = None
           for line in data:
             match = unused_line.match(line)
             if match:
               return int(match.group(1))
             match = used_line.match(line)
             if match:
               minor = int(match.group(1))
               highest = max(highest, minor)
           if highest is None: # there are no minors in use at all
             return 0
           if highest >= cls._MAX_MINORS:
             logging.error("Error: no free drbd minors!")
             raise errors.BlockDeviceError("Can't find a free DRBD minor")
           return highest + 1
         @classmethod
         def _IsValidMeta(cls, meta_device):
           """Check if the given meta device looks like a valid one.
           """
           minor = cls._FindUnusedMinor()
           minor_path = cls._DevPath(minor)
           result = utils.RunCmd(["drbdmeta", minor_path,
                                  "v08", meta_device, "0",
                                  "dstate"])
           if result.failed:
             logging.error("Invalid meta device %s: %s", meta_device, result.output)
             return False
           return True
         @classmethod
         def _GetShowParser(cls):
           """Return a parser for `drbd show` output.
           This will either create or return an already-create parser for the
           output of the command `drbd show`.
           """
           if cls._PARSE_SHOW is not None:
             return cls._PARSE_SHOW
           # pyparsing setup
           lbrace = pyp.Literal("{").suppress()
           rbrace = pyp.Literal("}").suppress()
           semi = pyp.Literal(";").suppress()
           # this also converts the value to an int
           number = pyp.Word(pyp.nums).setParseAction(lambda s, l, t: int(t[0]))
           comment = pyp.Literal ("#") + pyp.Optional(pyp.restOfLine)
           defa = pyp.Literal("_is_default").suppress()
           dbl_quote = pyp.Literal('"').suppress()
           keyword = pyp.Word(pyp.alphanums + '-')
           # value types
           value = pyp.Word(pyp.alphanums + '_-/.:')
           quoted = dbl_quote + pyp.CharsNotIn('"') + dbl_quote
           addr_port = (pyp.Word(pyp.nums + '.') + pyp.Literal(':').suppress() +
                        number)
           # meta device, extended syntax
           meta_value = ((value ^ quoted) + pyp.Literal('[').suppress() +
                         number + pyp.Word(']').suppress())
           # a statement
           stmt = (~rbrace + keyword + ~lbrace +
                   pyp.Optional(addr_port ^ value ^ quoted ^ meta_value) +
                   pyp.Optional(defa) + semi +
                   pyp.Optional(pyp.restOfLine).suppress())
           # an entire section
           section_name = pyp.Word(pyp.alphas + '_')
           section = section_name + lbrace + pyp.ZeroOrMore(pyp.Group(stmt)) + rbrace
           bnf = pyp.ZeroOrMore(pyp.Group(section ^ stmt))
           bnf.ignore(comment)
           cls._PARSE_SHOW = bnf
           return bnf
         @classmethod
         def _GetShowData(cls, minor):
           """Return the `drbdsetup show` data for a minor.
           """
           result = utils.RunCmd(["drbdsetup", cls._DevPath(minor), "show"])
           if result.failed:
             logging.error("Can't display the drbd config: %s - %s",
                           result.fail_reason, result.output)
             return None
           return result.stdout
         @classmethod
         def _GetDevInfo(cls, out):
           """Parse details about a given DRBD minor.
           This return, if available, the local backing device (as a path)
           and the local and remote (ip, port) information from a string
           containing the output of the `drbdsetup show` command as returned
           by _GetShowData.
           """
           data = {}
           if not out:
             return data
           bnf = cls._GetShowParser()
           # run pyparse
           try:
             results = bnf.parseString(out)
           except pyp.ParseException, err:
             raise errors.BlockDeviceError("Can't parse drbdsetup show output: %s" %
                                           str(err))
           # and massage the results into our desired format
           for section in results:
             sname = section[0]
             if sname == "_this_host":
               for lst in section[1:]:
                 if lst[0] == "disk":
                   data["local_dev"] = lst[1]
                 elif lst[0] == "meta-disk":
                   data["meta_dev"] = lst[1]
                   data["meta_index"] = lst[2]
                 elif lst[0] == "address":
                   data["local_addr"] = tuple(lst[1:])
             elif sname == "_remote_host":
               for lst in section[1:]:
                 if lst[0] == "address":
                   data["remote_addr"] = tuple(lst[1:])
           return data
         def _MatchesLocal(self, info):
           """Test if our local config matches with an existing device.
           The parameter should be as returned from `_GetDevInfo()`. This
           method tests if our local backing device is the same as the one in
           the info parameter, in effect testing if we look like the given
           device.
           """
           if self._children:
             backend, meta = self._children
           else:
             backend = meta = None
           if backend is not None:
             retval = ("local_dev" in info and info["local_dev"] == backend.dev_path)
           else:
             retval = ("local_dev" not in info)
           if meta is not None:
             retval = retval and ("meta_dev" in info and
                                  info["meta_dev"] == meta.dev_path)
             retval = retval and ("meta_index" in info and
                                  info["meta_index"] == 0)
           else:
             retval = retval and ("meta_dev" not in info and
                                  "meta_index" not in info)
           return retval
         def _MatchesNet(self, info):
           """Test if our network config matches with an existing device.
           The parameter should be as returned from `_GetDevInfo()`. This
           method tests if our network configuration is the same as the one
           in the info parameter, in effect testing if we look like the given
           device.
           """
           if (((self._lhost is None and not ("local_addr" in info)) and
                (self._rhost is None and not ("remote_addr" in info)))):
             return True
           if self._lhost is None:
             return False
           if not ("local_addr" in info and
                   "remote_addr" in info):
             return False
           retval = (info["local_addr"] == (self._lhost, self._lport))
           retval = (retval and
                     info["remote_addr"] == (self._rhost, self._rport))
           return retval
         @classmethod
         def _AssembleLocal(cls, minor, backend, meta):
           """Configure the local part of a DRBD device.
           This is the first thing that must be done on an unconfigured DRBD
           device. And it must be done only once.
           """
           if not cls._IsValidMeta(meta):
             return False
           args = ["drbdsetup", cls._DevPath(minor), "disk",
                   backend, meta, "0", "-e", "detach", "--create-device"]
           result = utils.RunCmd(args)
           if result.failed:
             logging.error("Can't attach local disk: %s", result.output)
           return not result.failed
         @classmethod
         def _AssembleNet(cls, minor, net_info, protocol,
                          dual_pri=False, hmac=None, secret=None):
           """Configure the network part of the device.
           """
           lhost, lport, rhost, rport = net_info
           if None in net_info:
             # we don't want network connection and actually want to make
             # sure its shutdown
             return cls._ShutdownNet(minor)
           # Workaround for a race condition. When DRBD is doing its dance to
           # establish a connection with its peer, it also sends the
           # synchronization speed over the wire. In some cases setting the
           # sync speed only after setting up both sides can race with DRBD
           # connecting, hence we set it here before telling DRBD anything
           # about its peer.
           cls._SetMinorSyncSpeed(minor, constants.SYNC_SPEED)
           args = ["drbdsetup", cls._DevPath(minor), "net",
                   "%s:%s" % (lhost, lport), "%s:%s" % (rhost, rport), protocol,
                   "-A", "discard-zero-changes",
                   "-B", "consensus",
                   "--create-device",
+                  ]
           if dual_pri:
             args.append("-m")
           if hmac and secret:
             args.extend(["-a", hmac, "-x", secret])
           result = utils.RunCmd(args)
           if result.failed:
             logging.error("Can't setup network for dbrd device: %s - %s",
                           result.fail_reason, result.output)
             return False
           timeout = time.time() + 10
           ok = False
           while time.time() < timeout:
             info = cls._GetDevInfo(cls._GetShowData(minor))
             if not "local_addr" in info or not "remote_addr" in info:
               time.sleep(1)
               continue
             if (info["local_addr"] != (lhost, lport) or
                 info["remote_addr"] != (rhost, rport)):
               time.sleep(1)
               continue
             ok = True
             break
           if not ok:
             logging.error("Timeout while configuring network")
             return False
           return True
         def AddChildren(self, devices):
           """Add a disk to the DRBD device.
           """
           if self.minor is None:
             raise errors.BlockDeviceError("Can't attach to dbrd8 during AddChildren")
           if len(devices) != 2:
             raise errors.BlockDeviceError("Need two devices for AddChildren")
           info = self._GetDevInfo(self._GetShowData(self.minor))
           if "local_dev" in info:
             raise errors.BlockDeviceError("DRBD8 already attached to a local disk")
           backend, meta = devices
           if backend.dev_path is None or meta.dev_path is None:
             raise errors.BlockDeviceError("Children not ready during AddChildren")
           backend.Open()
           meta.Open()
           if not self._CheckMetaSize(meta.dev_path):
             raise errors.BlockDeviceError("Invalid meta device size")
           self._InitMeta(self._FindUnusedMinor(), meta.dev_path)
           if not self._IsValidMeta(meta.dev_path):
             raise errors.BlockDeviceError("Cannot initalize meta device")
           if not self._AssembleLocal(self.minor, backend.dev_path, meta.dev_path):
             raise errors.BlockDeviceError("Can't attach to local storage")
           self._children = devices
         def RemoveChildren(self, devices):
           """Detach the drbd device from local storage.
           """
           if self.minor is None:
             raise errors.BlockDeviceError("Can't attach to drbd8 during"
                                           " RemoveChildren")
           # early return if we don't actually have backing storage
           info = self._GetDevInfo(self._GetShowData(self.minor))
           if "local_dev" not in info:
             return
           if len(self._children) != 2:
             raise errors.BlockDeviceError("We don't have two children: %s" %
                                           self._children)
           if self._children.count(None) == 2: # we don't actually have children :)
             logging.error("Requested detach while detached")
             return
           if len(devices) != 2:
             raise errors.BlockDeviceError("We need two children in RemoveChildren")
           for child, dev in zip(self._children, devices):
             if dev != child.dev_path:
               raise errors.BlockDeviceError("Mismatch in local storage"
                                             " (%s != %s) in RemoveChildren" %
                                             (dev, child.dev_path))
           if not self._ShutdownLocal(self.minor):
             raise errors.BlockDeviceError("Can't detach from local storage")
           self._children = []
         @classmethod
         def _SetMinorSyncSpeed(cls, minor, kbytes):
           """Set the speed of the DRBD syncer.
           This is the low-level implementation.
           @type minor: int
           @param minor: the drbd minor whose settings we change
           @type kbytes: int
           @param kbytes: the speed in kbytes/second
           @rtype: boolean
           @return: the success of the operation
           """
           result = utils.RunCmd(["drbdsetup", cls._DevPath(minor), "syncer",
                                  "-r", "%d" % kbytes, "--create-device"])
           if result.failed:
             logging.error("Can't change syncer rate: %s - %s",
                           result.fail_reason, result.output)
           return not result.failed
         def SetSyncSpeed(self, kbytes):
           """Set the speed of the DRBD syncer.
           @type kbytes: int
           @param kbytes: the speed in kbytes/second
           @rtype: boolean
           @return: the success of the operation
           """
           if self.minor is None:
             logging.info("Not attached during SetSyncSpeed")
             return False
           children_result = super(DRBD8, self).SetSyncSpeed(kbytes)
           return self._SetMinorSyncSpeed(self.minor, kbytes) and children_result
         def GetProcStatus(self):
           """Return device data from /proc.
           """
           if self.minor is None:
             raise errors.BlockDeviceError("GetStats() called while not attached")
           proc_info = self._MassageProcData(self._GetProcData())
           if self.minor not in proc_info:
             raise errors.BlockDeviceError("Can't find myself in /proc (minor %d)" %
                                           self.minor)
           return DRBD8Status(proc_info[self.minor])
         def GetSyncStatus(self):
           """Returns the sync status of the device.
           If sync_percent is None, it means all is ok
           If estimated_time is None, it means we can't esimate
           the time needed, otherwise it's the time left in seconds.
           We set the is_degraded parameter to True on two conditions:
           network not connected or local disk missing.
           We compute the ldisk parameter based on wheter we have a local
           disk or not.
           @rtype: tuple
           @return: (sync_percent, estimated_time, is_degraded, ldisk)
           """
           if self.minor is None and not self.Attach():
             raise errors.BlockDeviceError("Can't attach to device in GetSyncStatus")
           stats = self.GetProcStatus()
           ldisk = not stats.is_disk_uptodate
           is_degraded = not stats.is_connected
           return stats.sync_percent, stats.est_time, is_degraded or ldisk, ldisk
         def Open(self, force=False):
           """Make the local state primary.
           If the 'force' parameter is given, the '-o' option is passed to
           drbdsetup. Since this is a potentially dangerous operation, the
           force flag should be only given after creation, when it actually
           is mandatory.
           """
           if self.minor is None and not self.Attach():
             logging.error("DRBD cannot attach to a device during open")
             return False
           cmd = ["drbdsetup", self.dev_path, "primary"]
           if force:
             cmd.append("-o")
           result = utils.RunCmd(cmd)
           if result.failed:
             msg = ("Can't make drbd device primary: %s" % result.output)
             logging.error(msg)
             raise errors.BlockDeviceError(msg)
         def Close(self):
           """Make the local state secondary.
           This will, of course, fail if the device is in use.
           """
           if self.minor is None and not self.Attach():
             logging.info("Instance not attached to a device")
             raise errors.BlockDeviceError("Can't find device")
           result = utils.RunCmd(["drbdsetup", self.dev_path, "secondary"])
           if result.failed:
             msg = ("Can't switch drbd device to"
                    " secondary: %s" % result.output)
             logging.error(msg)
             raise errors.BlockDeviceError(msg)
         def DisconnectNet(self):
           """Removes network configuration.
           This method shutdowns the network side of the device.
           The method will wait up to a hardcoded timeout for the device to
           go into standalone after the 'disconnect' command before
           re-configuring it, as sometimes it takes a while for the
           disconnect to actually propagate and thus we might issue a 'net'
           command while the device is still connected. If the device will
           still be attached to the network and we time out, we raise an
           exception.
           """
           if self.minor is None:
             raise errors.BlockDeviceError("DRBD disk not attached in re-attach net")
           if None in (self._lhost, self._lport, self._rhost, self._rport):
             raise errors.BlockDeviceError("DRBD disk missing network info in"
                                           " DisconnectNet()")
           ever_disconnected = self._ShutdownNet(self.minor)
           timeout_limit = time.time() + self._NET_RECONFIG_TIMEOUT
           sleep_time = 0.100 # we start the retry time at 100 miliseconds
           while time.time() < timeout_limit:
             status = self.GetProcStatus()
             if status.is_standalone:
               break
             # retry the disconnect, it seems possible that due to a
             # well-time disconnect on the peer, my disconnect command might
             # be ingored and forgotten
             ever_disconnected = self._ShutdownNet(self.minor) or ever_disconnected
             time.sleep(sleep_time)
             sleep_time = min(2, sleep_time * 1.5)
           if not status.is_standalone:
             if ever_disconnected:
               msg = ("Device did not react to the"
                      " 'disconnect' command in a timely manner")
             else:
               msg = ("Can't shutdown network, even after multiple retries")
             raise errors.BlockDeviceError(msg)
           reconfig_time = time.time() - timeout_limit + self._NET_RECONFIG_TIMEOUT
           if reconfig_time > 15: # hardcoded alert limit
             logging.debug("DRBD8.DisconnectNet: detach took %.3f seconds",
                           reconfig_time)
         def AttachNet(self, multimaster):
           """Reconnects the network.
           This method connects the network side of the device with a
           specified multi-master flag. The device needs to be 'Standalone'
           but have valid network configuration data.
           Args:
             - multimaster: init the network in dual-primary mode
           """
           if self.minor is None:
             raise errors.BlockDeviceError("DRBD disk not attached in AttachNet")
           if None in (self._lhost, self._lport, self._rhost, self._rport):
             raise errors.BlockDeviceError("DRBD disk missing network info in"
                                           " AttachNet()")
           status = self.GetProcStatus()
           if not status.is_standalone:
             raise errors.BlockDeviceError("Device is not standalone in AttachNet")
           return self._AssembleNet(self.minor,
                                    (self._lhost, self._lport,
                                     self._rhost, self._rport),
                                    "C", dual_pri=multimaster)
         def Attach(self):
           """Check if our minor is configured.
           This doesn't do any device configurations - it only checks if the
           minor is in a state different from Unconfigured.
           Note that this function will not change the state of the system in
           any way (except in case of side-effects caused by reading from
           /proc).
           """
           used_devs = self._GetUsedDevs()
           if self._aminor in used_devs:
             minor = self._aminor
           else:
             minor = None
           self._SetFromMinor(minor)
           return minor is not None
         def Assemble(self):
           """Assemble the drbd.
           Method:
             - if we have a configured device, we try to ensure that it matches
               our config
             - if not, we create it from zero
           """
           result = super(DRBD8, self).Assemble()
           if not result:
             return result
           self.Attach()
           if self.minor is None:
             # local device completely unconfigured
             return self._FastAssemble()
           else:
             # we have to recheck the local and network status and try to fix
             # the device
             return self._SlowAssemble()
         def _SlowAssemble(self):
           """Assembles the DRBD device from a (partially) configured device.
           In case of partially attached (local device matches but no network
           setup), we perform the network attach. If successful, we re-test
           the attach if can return success.
           """
           for minor in (self._aminor,):
             info = self._GetDevInfo(self._GetShowData(minor))
             match_l = self._MatchesLocal(info)
             match_r = self._MatchesNet(info)
             if match_l and match_r:
               break
             if match_l and not match_r and "local_addr" not in info:
               res_r = self._AssembleNet(minor,
                                         (self._lhost, self._lport,
                                          self._rhost, self._rport),
                                         constants.DRBD_NET_PROTOCOL,
                                         hmac=constants.DRBD_HMAC_ALG,
                                         secret=self._secret
+                                        )
               if res_r:
                 if self._MatchesNet(self._GetDevInfo(self._GetShowData(minor))):
                   break
             # the weakest case: we find something that is only net attached
             # even though we were passed some children at init time
             if match_r and "local_dev" not in info:
               break
             # this case must be considered only if we actually have local
             # storage, i.e. not in diskless mode, because all diskless
             # devices are equal from the point of view of local
             # configuration
             if (match_l and "local_dev" in info and
                 not match_r and "local_addr" in info):
               # strange case - the device network part points to somewhere
               # else, even though its local storage is ours; as we own the
               # drbd space, we try to disconnect from the remote peer and
               # reconnect to our correct one
               if not self._ShutdownNet(minor):
                 raise errors.BlockDeviceError("Device has correct local storage,"
                                               " wrong remote peer and is unable to"
                                               " disconnect in order to attach to"
                                               " the correct peer")
               # note: _AssembleNet also handles the case when we don't want
               # local storage (i.e. one or more of the _[lr](host|port) is
               # None)
               if (self._AssembleNet(minor, (self._lhost, self._lport,
                                             self._rhost, self._rport),
                                     constants.DRBD_NET_PROTOCOL,
                                     hmac=constants.DRBD_HMAC_ALG,
                                     secret=self._secret) and
                   self._MatchesNet(self._GetDevInfo(self._GetShowData(minor)))):
                 break
           else:
             minor = None
           self._SetFromMinor(minor)
           return minor is not None
         def _FastAssemble(self):
           """Assemble the drbd device from zero.
           This is run when in Assemble we detect our minor is unused.
           """
           # TODO: maybe completely tear-down the minor (drbdsetup ... down)
           # before attaching our own?
           minor = self._aminor
           need_localdev_teardown = False
           if self._children and self._children[0] and self._children[1]:
             result = self._AssembleLocal(minor, self._children[0].dev_path,
                                          self._children[1].dev_path)
             if not result:
               return False
             need_localdev_teardown = True
           if self._lhost and self._lport and self._rhost and self._rport:
             result = self._AssembleNet(minor,
                                        (self._lhost, self._lport,
                                         self._rhost, self._rport),
                                        constants.DRBD_NET_PROTOCOL,
                                        hmac=constants.DRBD_HMAC_ALG,
                                        secret=self._secret)
             if not result:
               if need_localdev_teardown:
                 # we will ignore failures from this
                 logging.error("net setup failed, tearing down local device")
                 self._ShutdownAll(minor)
               return False
           self._SetFromMinor(minor)
           return True
         @classmethod
         def _ShutdownLocal(cls, minor):
           """Detach from the local device.
           I/Os will continue to be served from the remote device. If we
           don't have a remote device, this operation will fail.
           """
           result = utils.RunCmd(["drbdsetup", cls._DevPath(minor), "detach"])
           if result.failed:
             logging.error("Can't detach local device: %s", result.output)
           return not result.failed
         @classmethod
         def _ShutdownNet(cls, minor):
           """Disconnect from the remote peer.
           This fails if we don't have a local device.
           """
           result = utils.RunCmd(["drbdsetup", cls._DevPath(minor), "disconnect"])
           if result.failed:
             logging.error("Can't shutdown network: %s", result.output)
           return not result.failed
         @classmethod
         def _ShutdownAll(cls, minor):
           """Deactivate the device.
           This will, of course, fail if the device is in use.
           """
           result = utils.RunCmd(["drbdsetup", cls._DevPath(minor), "down"])
           if result.failed:
             logging.error("Can't shutdown drbd device: %s", result.output)
           return not result.failed
         def Shutdown(self):
           """Shutdown the DRBD device.
           """
           if self.minor is None and not self.Attach():
             logging.info("DRBD device not attached to a device during Shutdown")
             return True
           if not self._ShutdownAll(self.minor):
             return False
           self.minor = None
           self.dev_path = None
           return True
         def Remove(self):
           """Stub remove for DRBD devices.
           """
           return self.Shutdown()
         @classmethod
         def Create(cls, unique_id, children, size):
           """Create a new DRBD8 device.
           Since DRBD devices are not created per se, just assembled, this
           function only initializes the metadata.
           """
           if len(children) != 2:
             raise errors.ProgrammerError("Invalid setup for the drbd device")
           meta = children[1]
           meta.Assemble()
           if not meta.Attach():
             raise errors.BlockDeviceError("Can't attach to meta device")
           if not cls._CheckMetaSize(meta.dev_path):
             raise errors.BlockDeviceError("Invalid meta device size")
           cls._InitMeta(cls._FindUnusedMinor(), meta.dev_path)
           if not cls._IsValidMeta(meta.dev_path):
             raise errors.BlockDeviceError("Cannot initalize meta device")
           return cls(unique_id, children)
         def Grow(self, amount):
           """Resize the DRBD device and its backing storage.
           """
           if self.minor is None:
             raise errors.ProgrammerError("drbd8: Grow called while not attached")
           if len(self._children) != 2 or None in self._children:
             raise errors.BlockDeviceError("Cannot grow diskless DRBD8 device")
           self._children[0].Grow(amount)
           result = utils.RunCmd(["drbdsetup", self.dev_path, "resize"])
           if result.failed:
             raise errors.BlockDeviceError("resize failed for %s: %s" %
                                           (self.dev_path, result.output))
           return
       class FileStorage(BlockDev):
         """File device.
         This class represents the a file storage backend device.
         The unique_id for the file device is a (file_driver, file_path) tuple.
         """
         def __init__(self, unique_id, children):
           """Initalizes a file device backend.
           """
           if children:
             raise errors.BlockDeviceError("Invalid setup for file device")
           super(FileStorage, self).__init__(unique_id, children)
           if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
             raise ValueError("Invalid configuration data %s" % str(unique_id))
           self.driver = unique_id[0]
           self.dev_path = unique_id[1]
           self.Attach()
         def Assemble(self):
           """Assemble the device.
           Checks whether the file device exists, raises BlockDeviceError otherwise.
           """
           if not os.path.exists(self.dev_path):
             raise errors.BlockDeviceError("File device '%s' does not exist." %
                                           self.dev_path)
           return True
         def Shutdown(self):
           """Shutdown the device.
           This is a no-op for the file type, as we don't deacivate
           the file on shutdown.
           """
           return True
         def Open(self, force=False):
           """Make the device ready for I/O.
           This is a no-op for the file type.
           """
           pass
         def Close(self):
           """Notifies that the device will no longer be used for I/O.
           This is a no-op for the file type.
           """
           pass
         def Remove(self):
           """Remove the file backing the block device.
           @rtype: boolean
           @return: True if the removal was successful
           """
           if not os.path.exists(self.dev_path):
             return True
           try:
             os.remove(self.dev_path)
             return True
           except OSError, err:
             logging.error("Can't remove file '%s': %s", self.dev_path, err)
             return False
         def Attach(self):
           """Attach to an existing file.
           Check if this file already exists.
           @rtype: boolean
           @return: True if file exists
           """
           self.attached = os.path.exists(self.dev_path)
           return self.attached
         @classmethod
         def Create(cls, unique_id, children, size):
           """Create a new file.
           @param size: the size of file in MiB
           @rtype: L{bdev.FileStorage}
           @return: an instance of FileStorage
           """
           if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
             raise ValueError("Invalid configuration data %s" % str(unique_id))
           dev_path = unique_id[1]
           try:
             f = open(dev_path, 'w')
           except IOError, err:
             raise errors.BlockDeviceError("Could not create '%'" % err)
           else:
             f.truncate(size * 1024 * 1024)
             f.close()
           return FileStorage(unique_id, children)
       DEV_MAP = {
         constants.LD_LV: LogicalVolume,
         constants.LD_DRBD8: DRBD8,
         constants.LD_FILE: FileStorage,
+        }
       def FindDevice(dev_type, unique_id, children):
         """Search for an existing, assembled device.
         This will succeed only if the device exists and is assembled, but it
         does not do any actions in order to activate the device.
         """
         if dev_type not in DEV_MAP:
           raise errors.ProgrammerError("Invalid block device type '%s'" % dev_type)
         device = DEV_MAP[dev_type](unique_id, children)
         if not device.attached:
           return None
         return device
       def Assemble(dev_type, unique_id, children):
         """Try to attach or assemble an existing device.
         This will attach to assemble the device, as needed, to bring it
         fully up. It must be safe to run on already-assembled devices.
         """
         if dev_type not in DEV_MAP:
           raise errors.ProgrammerError("Invalid block device type '%s'" % dev_type)
         device = DEV_MAP[dev_type](unique_id, children)
         if not device.Assemble():
           raise errors.BlockDeviceError("Can't find a valid block device for"
                                         " %s/%s/%s" %
                                         (dev_type, unique_id, children))
         return device
       def Create(dev_type, unique_id, children, size):
         """Create a device.
         """
         if dev_type not in DEV_MAP:
           raise errors.ProgrammerError("Invalid block device type '%s'" % dev_type)
         device = DEV_MAP[dev_type].Create(unique_id, children, size)
         return device

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