[ganeti-local] / lib / block / bdev.py

#
#

# Copyright (C) 2006, 2007, 2010, 2011, 2012, 2013 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 errno
import stat
import os
import logging
import math

from ganeti import utils
from ganeti import errors
from ganeti import constants
from ganeti import objects
from ganeti import compat
from ganeti import pathutils
from ganeti import serializer
from ganeti.block import drbd
from ganeti.block import base


class RbdShowmappedJsonError(Exception):
  """`rbd showmmapped' JSON formatting error Exception class.

  """
  pass


def _CheckResult(result):
  """Throws an error if the given result is a failed one.

  @param result: result from RunCmd

  """
  if result.failed:
    base.ThrowError("Command: %s error: %s - %s",
                    result.cmd, result.fail_reason, result.output)


def _GetForbiddenFileStoragePaths():
  """Builds a list of path prefixes which shouldn't be used for file storage.

  @rtype: frozenset

  """
  paths = set([
    "/boot",
    "/dev",
    "/etc",
    "/home",
    "/proc",
    "/root",
    "/sys",
    ])

  for prefix in ["", "/usr", "/usr/local"]:
    paths.update(map(lambda s: "%s/%s" % (prefix, s),
                     ["bin", "lib", "lib32", "lib64", "sbin"]))

  return compat.UniqueFrozenset(map(os.path.normpath, paths))


def _ComputeWrongFileStoragePaths(paths,
                                  _forbidden=_GetForbiddenFileStoragePaths()):
  """Cross-checks a list of paths for prefixes considered bad.

  Some paths, e.g. "/bin", should not be used for file storage.

  @type paths: list
  @param paths: List of paths to be checked
  @rtype: list
  @return: Sorted list of paths for which the user should be warned

  """
  def _Check(path):
    return (not os.path.isabs(path) or
            path in _forbidden or
            filter(lambda p: utils.IsBelowDir(p, path), _forbidden))

  return utils.NiceSort(filter(_Check, map(os.path.normpath, paths)))


def ComputeWrongFileStoragePaths(_filename=pathutils.FILE_STORAGE_PATHS_FILE):
  """Returns a list of file storage paths whose prefix is considered bad.

  See L{_ComputeWrongFileStoragePaths}.

  """
  return _ComputeWrongFileStoragePaths(_LoadAllowedFileStoragePaths(_filename))


def _CheckFileStoragePath(path, allowed):
  """Checks if a path is in a list of allowed paths for file storage.

  @type path: string
  @param path: Path to check
  @type allowed: list
  @param allowed: List of allowed paths
  @raise errors.FileStoragePathError: If the path is not allowed

  """
  if not os.path.isabs(path):
    raise errors.FileStoragePathError("File storage path must be absolute,"
                                      " got '%s'" % path)

  for i in allowed:
    if not os.path.isabs(i):
      logging.info("Ignoring relative path '%s' for file storage", i)
      continue

    if utils.IsBelowDir(i, path):
      break
  else:
    raise errors.FileStoragePathError("Path '%s' is not acceptable for file"
                                      " storage" % path)


def _LoadAllowedFileStoragePaths(filename):
  """Loads file containing allowed file storage paths.

  @rtype: list
  @return: List of allowed paths (can be an empty list)

  """
  try:
    contents = utils.ReadFile(filename)
  except EnvironmentError:
    return []
  else:
    return utils.FilterEmptyLinesAndComments(contents)


def CheckFileStoragePath(path, _filename=pathutils.FILE_STORAGE_PATHS_FILE):
  """Checks if a path is allowed for file storage.

  @type path: string
  @param path: Path to check
  @raise errors.FileStoragePathError: If the path is not allowed

  """
  allowed = _LoadAllowedFileStoragePaths(_filename)

  if _ComputeWrongFileStoragePaths([path]):
    raise errors.FileStoragePathError("Path '%s' uses a forbidden prefix" %
                                      path)

  _CheckFileStoragePath(path, allowed)


class LogicalVolume(base.BlockDev):
  """Logical Volume block device.

  """
  _VALID_NAME_RE = re.compile("^[a-zA-Z0-9+_.-]*$")
  _INVALID_NAMES = compat.UniqueFrozenset([".", "..", "snapshot", "pvmove"])
  _INVALID_SUBSTRINGS = compat.UniqueFrozenset(["_mlog", "_mimage"])

  def __init__(self, unique_id, children, size, params):
    """Attaches to a LV device.

    The unique_id is a tuple (vg_name, lv_name)

    """
    super(LogicalVolume, self).__init__(unique_id, children, size, params)
    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._ValidateName(self._vg_name)
    self._ValidateName(self._lv_name)
    self.dev_path = utils.PathJoin("/dev", self._vg_name, self._lv_name)
    self._degraded = True
    self.major = self.minor = self.pe_size = self.stripe_count = None
    self.Attach()

  @staticmethod
  def _GetStdPvSize(pvs_info):
    """Return the the standard PV size (used with exclusive storage).

    @param pvs_info: list of objects.LvmPvInfo, cannot be empty
    @rtype: float
    @return: size in MiB

    """
    assert len(pvs_info) > 0
    smallest = min([pv.size for pv in pvs_info])
    return smallest / (1 + constants.PART_MARGIN + constants.PART_RESERVED)

  @staticmethod
  def _ComputeNumPvs(size, pvs_info):
    """Compute the number of PVs needed for an LV (with exclusive storage).

    @type size: float
    @param size: LV size in MiB
    @param pvs_info: list of objects.LvmPvInfo, cannot be empty
    @rtype: integer
    @return: number of PVs needed
    """
    assert len(pvs_info) > 0
    pv_size = float(LogicalVolume._GetStdPvSize(pvs_info))
    return int(math.ceil(float(size) / pv_size))

  @staticmethod
  def _GetEmptyPvNames(pvs_info, max_pvs=None):
    """Return a list of empty PVs, by name.

    """
    empty_pvs = filter(objects.LvmPvInfo.IsEmpty, pvs_info)
    if max_pvs is not None:
      empty_pvs = empty_pvs[:max_pvs]
    return map((lambda pv: pv.name), empty_pvs)

  @classmethod
  def Create(cls, unique_id, children, size, params, excl_stor):
    """Create a new logical volume.

    """
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise errors.ProgrammerError("Invalid configuration data %s" %
                                   str(unique_id))
    vg_name, lv_name = unique_id
    cls._ValidateName(vg_name)
    cls._ValidateName(lv_name)
    pvs_info = cls.GetPVInfo([vg_name])
    if not pvs_info:
      if excl_stor:
        msg = "No (empty) PVs found"
      else:
        msg = "Can't compute PV info for vg %s" % vg_name
      base.ThrowError(msg)
    pvs_info.sort(key=(lambda pv: pv.free), reverse=True)

    pvlist = [pv.name for pv in pvs_info]
    if compat.any(":" in v for v in pvlist):
      base.ThrowError("Some of your PVs have the invalid character ':' in their"
                      " name, this is not supported - please filter them out"
                      " in lvm.conf using either 'filter' or 'preferred_names'")

    current_pvs = len(pvlist)
    desired_stripes = params[constants.LDP_STRIPES]
    stripes = min(current_pvs, desired_stripes)

    if excl_stor:
      (err_msgs, _) = utils.LvmExclusiveCheckNodePvs(pvs_info)
      if err_msgs:
        for m in err_msgs:
          logging.warning(m)
      req_pvs = cls._ComputeNumPvs(size, pvs_info)
      pvlist = cls._GetEmptyPvNames(pvs_info, req_pvs)
      current_pvs = len(pvlist)
      if current_pvs < req_pvs:
        base.ThrowError("Not enough empty PVs to create a disk of %d MB:"
                        " %d available, %d needed", size, current_pvs, req_pvs)
      assert current_pvs == len(pvlist)
      if stripes > current_pvs:
        # No warning issued for this, as it's no surprise
        stripes = current_pvs

    else:
      if stripes < desired_stripes:
        logging.warning("Could not use %d stripes for VG %s, as only %d PVs are"
                        " available.", desired_stripes, vg_name, current_pvs)
      free_size = sum([pv.free for pv in pvs_info])
      # The size constraint should have been checked from the master before
      # calling the create function.
      if free_size < size:
        base.ThrowError("Not enough free space: required %s,"
                        " available %s", size, free_size)

    # If the free space is not well distributed, we won't be able to
    # create an optimally-striped volume; in that case, we want to try
    # with N, N-1, ..., 2, and finally 1 (non-stripped) number of
    # stripes
    cmd = ["lvcreate", "-L%dm" % size, "-n%s" % lv_name]
    for stripes_arg in range(stripes, 0, -1):
      result = utils.RunCmd(cmd + ["-i%d" % stripes_arg] + [vg_name] + pvlist)
      if not result.failed:
        break
    if result.failed:
      base.ThrowError("LV create failed (%s): %s",
                      result.fail_reason, result.output)
    return LogicalVolume(unique_id, children, size, params)

  @staticmethod
  def _GetVolumeInfo(lvm_cmd, fields):
    """Returns LVM Volume infos using lvm_cmd

    @param lvm_cmd: Should be one of "pvs", "vgs" or "lvs"
    @param fields: Fields to return
    @return: A list of dicts each with the parsed fields

    """
    if not fields:
      raise errors.ProgrammerError("No fields specified")

    sep = "|"
    cmd = [lvm_cmd, "--noheadings", "--nosuffix", "--units=m", "--unbuffered",
           "--separator=%s" % sep, "-o%s" % ",".join(fields)]

    result = utils.RunCmd(cmd)
    if result.failed:
      raise errors.CommandError("Can't get the volume information: %s - %s" %
                                (result.fail_reason, result.output))

    data = []
    for line in result.stdout.splitlines():
      splitted_fields = line.strip().split(sep)

      if len(fields) != len(splitted_fields):
        raise errors.CommandError("Can't parse %s output: line '%s'" %
                                  (lvm_cmd, line))

      data.append(splitted_fields)

    return data

  @classmethod
  def GetPVInfo(cls, vg_names, filter_allocatable=True, include_lvs=False):
    """Get the free space info for PVs in a volume group.

    @param vg_names: list of volume group names, if empty all will be returned
    @param filter_allocatable: whether to skip over unallocatable PVs
    @param include_lvs: whether to include a list of LVs hosted on each PV

    @rtype: list
    @return: list of objects.LvmPvInfo objects

    """
    # We request "lv_name" field only if we care about LVs, so we don't get
    # a long list of entries with many duplicates unless we really have to.
    # The duplicate "pv_name" field will be ignored.
    if include_lvs:
      lvfield = "lv_name"
    else:
      lvfield = "pv_name"
    try:
      info = cls._GetVolumeInfo("pvs", ["pv_name", "vg_name", "pv_free",
                                        "pv_attr", "pv_size", lvfield])
    except errors.GenericError, err:
      logging.error("Can't get PV information: %s", err)
      return None

    # When asked for LVs, "pvs" may return multiple entries for the same PV-LV
    # pair. We sort entries by PV name and then LV name, so it's easy to weed
    # out duplicates.
    if include_lvs:
      info.sort(key=(lambda i: (i[0], i[5])))
    data = []
    lastpvi = None
    for (pv_name, vg_name, pv_free, pv_attr, pv_size, lv_name) in info:
      # (possibly) skip over pvs which are not allocatable
      if filter_allocatable and pv_attr[0] != "a":
        continue
      # (possibly) skip over pvs which are not in the right volume group(s)
      if vg_names and vg_name not in vg_names:
        continue
      # Beware of duplicates (check before inserting)
      if lastpvi and lastpvi.name == pv_name:
        if include_lvs and lv_name:
          if not lastpvi.lv_list or lastpvi.lv_list[-1] != lv_name:
            lastpvi.lv_list.append(lv_name)
      else:
        if include_lvs and lv_name:
          lvl = [lv_name]
        else:
          lvl = []
        lastpvi = objects.LvmPvInfo(name=pv_name, vg_name=vg_name,
                                    size=float(pv_size), free=float(pv_free),
                                    attributes=pv_attr, lv_list=lvl)
        data.append(lastpvi)

    return data

  @classmethod
  def _GetExclusiveStorageVgFree(cls, vg_name):
    """Return the free disk space in the given VG, in exclusive storage mode.

    @type vg_name: string
    @param vg_name: VG name
    @rtype: float
    @return: free space in MiB
    """
    pvs_info = cls.GetPVInfo([vg_name])
    if not pvs_info:
      return 0.0
    pv_size = cls._GetStdPvSize(pvs_info)
    num_pvs = len(cls._GetEmptyPvNames(pvs_info))
    return pv_size * num_pvs

  @classmethod
  def GetVGInfo(cls, vg_names, excl_stor, filter_readonly=True):
    """Get the free space info for specific VGs.

    @param vg_names: list of volume group names, if empty all will be returned
    @param excl_stor: whether exclusive_storage is enabled
    @param filter_readonly: whether to skip over readonly VGs

    @rtype: list
    @return: list of tuples (free_space, total_size, name) with free_space in
             MiB

    """
    try:
      info = cls._GetVolumeInfo("vgs", ["vg_name", "vg_free", "vg_attr",
                                        "vg_size"])
    except errors.GenericError, err:
      logging.error("Can't get VG information: %s", err)
      return None

    data = []
    for vg_name, vg_free, vg_attr, vg_size in info:
      # (possibly) skip over vgs which are not writable
      if filter_readonly and vg_attr[0] == "r":
        continue
      # (possibly) skip over vgs which are not in the right volume group(s)
      if vg_names and vg_name not in vg_names:
        continue
      # Exclusive storage needs a different concept of free space
      if excl_stor:
        es_free = cls._GetExclusiveStorageVgFree(vg_name)
        assert es_free <= vg_free
        vg_free = es_free
      data.append((float(vg_free), float(vg_size), vg_name))

    return data

  @classmethod
  def _ValidateName(cls, name):
    """Validates that a given name is valid as VG or LV name.

    The list of valid characters and restricted names is taken out of
    the lvm(8) manpage, with the simplification that we enforce both
    VG and LV restrictions on the names.

    """
    if (not cls._VALID_NAME_RE.match(name) or
        name in cls._INVALID_NAMES or
        compat.any(substring in name for substring in cls._INVALID_SUBSTRINGS)):
      base.ThrowError("Invalid LVM name '%s'", name)

  def Remove(self):
    """Remove this logical volume.

    """
    if not self.minor and not self.Attach():
      # the LV does not exist
      return
    result = utils.RunCmd(["lvremove", "-f", "%s/%s" %
                           (self._vg_name, self._lv_name)])
    if result.failed:
      base.ThrowError("Can't lvremove: %s - %s",
                      result.fail_reason, result.output)

  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:
      base.ThrowError("Failed to rename the logical volume: %s", result.output)
    self._lv_name = new_name
    self.dev_path = utils.PathJoin("/dev", 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=,",
                           "--units=k", "--nosuffix",
                           "-olv_attr,lv_kernel_major,lv_kernel_minor,"
                           "vg_extent_size,stripes", 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
    # the output can (and will) have multiple lines for multi-segment
    # LVs, as the 'stripes' parameter is a segment one, so we take
    # only the last entry, which is the one we're interested in; note
    # that with LVM2 anyway the 'stripes' value must be constant
    # across segments, so this is a no-op actually
    out = result.stdout.splitlines()
    if not out: # totally empty result? splitlines() returns at least
                # one line for any non-empty string
      logging.error("Can't parse LVS output, no lines? Got '%s'", str(out))
      return False
    out = out[-1].strip().rstrip(",")
    out = out.split(",")
    if len(out) != 5:
      logging.error("Can't parse LVS output, len(%s) != 5", str(out))
      return False

    status, major, minor, pe_size, stripes = out
    if len(status) < 6:
      logging.error("lvs lv_attr is not at least 6 characters (%s)", status)
      return False

    try:
      major = int(major)
      minor = int(minor)
    except (TypeError, ValueError), err:
      logging.error("lvs major/minor cannot be parsed: %s", str(err))

    try:
      pe_size = int(float(pe_size))
    except (TypeError, ValueError), err:
      logging.error("Can't parse vg extent size: %s", err)
      return False

    try:
      stripes = int(stripes)
    except (TypeError, ValueError), err:
      logging.error("Can't parse the number of stripes: %s", err)
      return False

    self.major = major
    self.minor = minor
    self.pe_size = pe_size
    self.stripe_count = stripes
    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 always 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:
      base.ThrowError("Can't activate lv %s: %s", self.dev_path, result.output)

  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.

    """
    pass

  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: objects.BlockDevStatus

    """
    if self._degraded:
      ldisk_status = constants.LDS_FAULTY
    else:
      ldisk_status = constants.LDS_OKAY

    return objects.BlockDevStatus(dev_path=self.dev_path,
                                  major=self.major,
                                  minor=self.minor,
                                  sync_percent=None,
                                  estimated_time=None,
                                  is_degraded=self._degraded,
                                  ldisk_status=ldisk_status)

  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.

    @returns: tuple (vg, lv)

    """
    snap_name = self._lv_name + ".snap"

    # remove existing snapshot if found
    snap = LogicalVolume((self._vg_name, snap_name), None, size, self.params)
    base.IgnoreError(snap.Remove)

    vg_info = self.GetVGInfo([self._vg_name], False)
    if not vg_info:
      base.ThrowError("Can't compute VG info for vg %s", self._vg_name)
    free_size, _, _ = vg_info[0]
    if free_size < size:
      base.ThrowError("Not enough free space: required %s,"
                      " available %s", size, free_size)

    _CheckResult(utils.RunCmd(["lvcreate", "-L%dm" % size, "-s",
                               "-n%s" % snap_name, self.dev_path]))

    return (self._vg_name, snap_name)

  def _RemoveOldInfo(self):
    """Try to remove old tags from the lv.

    """
    result = utils.RunCmd(["lvs", "-o", "tags", "--noheadings", "--nosuffix",
                           self.dev_path])
    _CheckResult(result)

    raw_tags = result.stdout.strip()
    if raw_tags:
      for tag in raw_tags.split(","):
        _CheckResult(utils.RunCmd(["lvchange", "--deltag",
                                   tag.strip(), self.dev_path]))

  def SetInfo(self, text):
    """Update metadata with info text.

    """
    base.BlockDev.SetInfo(self, text)

    self._RemoveOldInfo()

    # 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]

    _CheckResult(utils.RunCmd(["lvchange", "--addtag", text, self.dev_path]))

  def Grow(self, amount, dryrun, backingstore):
    """Grow the logical volume.

    """
    if not backingstore:
      return
    if self.pe_size is None or self.stripe_count is None:
      if not self.Attach():
        base.ThrowError("Can't attach to LV during Grow()")
    full_stripe_size = self.pe_size * self.stripe_count
    # pe_size is in KB
    amount *= 1024
    rest = amount % full_stripe_size
    if rest != 0:
      amount += full_stripe_size - rest
    cmd = ["lvextend", "-L", "+%dk" % amount]
    if dryrun:
      cmd.append("--test")
    # 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(cmd + ["--alloc", alloc_policy, self.dev_path])
      if not result.failed:
        return
    base.ThrowError("Can't grow LV %s: %s", self.dev_path, result.output)


class FileStorage(base.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, size, params):
    """Initalizes a file device backend.

    """
    if children:
      raise errors.BlockDeviceError("Invalid setup for file device")
    super(FileStorage, self).__init__(unique_id, children, size, params)
    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]

    CheckFileStoragePath(self.dev_path)

    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):
      base.ThrowError("File device '%s' does not exist" % self.dev_path)

  def Shutdown(self):
    """Shutdown the device.

    This is a no-op for the file type, as we don't deactivate
    the file on shutdown.

    """
    pass

  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

    """
    try:
      os.remove(self.dev_path)
    except OSError, err:
      if err.errno != errno.ENOENT:
        base.ThrowError("Can't remove file '%s': %s", self.dev_path, err)

  def Rename(self, new_id):
    """Renames the file.

    """
    # TODO: implement rename for file-based storage
    base.ThrowError("Rename is not supported for file-based storage")

  def Grow(self, amount, dryrun, backingstore):
    """Grow the file

    @param amount: the amount (in mebibytes) to grow with

    """
    if not backingstore:
      return
    # Check that the file exists
    self.Assemble()
    current_size = self.GetActualSize()
    new_size = current_size + amount * 1024 * 1024
    assert new_size > current_size, "Cannot Grow with a negative amount"
    # We can't really simulate the growth
    if dryrun:
      return
    try:
      f = open(self.dev_path, "a+")
      f.truncate(new_size)
      f.close()
    except EnvironmentError, err:
      base.ThrowError("Error in file growth: %", str(err))

  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

  def GetActualSize(self):
    """Return the actual disk size.

    @note: the device needs to be active when this is called

    """
    assert self.attached, "BlockDevice not attached in GetActualSize()"
    try:
      st = os.stat(self.dev_path)
      return st.st_size
    except OSError, err:
      base.ThrowError("Can't stat %s: %s", self.dev_path, err)

  @classmethod
  def Create(cls, unique_id, children, size, params, excl_stor):
    """Create a new file.

    @param size: the size of file in MiB

    @rtype: L{bdev.FileStorage}
    @return: an instance of FileStorage

    """
    if excl_stor:
      raise errors.ProgrammerError("FileStorage device requested with"
                                   " exclusive_storage")
    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]

    CheckFileStoragePath(dev_path)

    try:
      fd = os.open(dev_path, os.O_RDWR | os.O_CREAT | os.O_EXCL)
      f = os.fdopen(fd, "w")
      f.truncate(size * 1024 * 1024)
      f.close()
    except EnvironmentError, err:
      if err.errno == errno.EEXIST:
        base.ThrowError("File already existing: %s", dev_path)
      base.ThrowError("Error in file creation: %", str(err))

    return FileStorage(unique_id, children, size, params)


class PersistentBlockDevice(base.BlockDev):
  """A block device with persistent node

  May be either directly attached, or exposed through DM (e.g. dm-multipath).
  udev helpers are probably required to give persistent, human-friendly
  names.

  For the time being, pathnames are required to lie under /dev.

  """
  def __init__(self, unique_id, children, size, params):
    """Attaches to a static block device.

    The unique_id is a path under /dev.

    """
    super(PersistentBlockDevice, self).__init__(unique_id, children, size,
                                                params)
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise ValueError("Invalid configuration data %s" % str(unique_id))
    self.dev_path = unique_id[1]
    if not os.path.realpath(self.dev_path).startswith("/dev/"):
      raise ValueError("Full path '%s' lies outside /dev" %
                              os.path.realpath(self.dev_path))
    # TODO: this is just a safety guard checking that we only deal with devices
    # we know how to handle. In the future this will be integrated with
    # external storage backends and possible values will probably be collected
    # from the cluster configuration.
    if unique_id[0] != constants.BLOCKDEV_DRIVER_MANUAL:
      raise ValueError("Got persistent block device of invalid type: %s" %
                       unique_id[0])

    self.major = self.minor = None
    self.Attach()

  @classmethod
  def Create(cls, unique_id, children, size, params, excl_stor):
    """Create a new device

    This is a noop, we only return a PersistentBlockDevice instance

    """
    if excl_stor:
      raise errors.ProgrammerError("Persistent block device requested with"
                                   " exclusive_storage")
    return PersistentBlockDevice(unique_id, children, 0, params)

  def Remove(self):
    """Remove a device

    This is a noop

    """
    pass

  def Rename(self, new_id):
    """Rename this device.

    """
    base.ThrowError("Rename is not supported for PersistentBlockDev storage")

  def Attach(self):
    """Attach to an existing block device.


    """
    self.attached = False
    try:
      st = os.stat(self.dev_path)
    except OSError, err:
      logging.error("Error stat()'ing %s: %s", self.dev_path, str(err))
      return False

    if not stat.S_ISBLK(st.st_mode):
      logging.error("%s is not a block device", self.dev_path)
      return False

    self.major = os.major(st.st_rdev)
    self.minor = os.minor(st.st_rdev)
    self.attached = True

    return True

  def Assemble(self):
    """Assemble the device.

    """
    pass

  def Shutdown(self):
    """Shutdown the device.

    """
    pass

  def Open(self, force=False):
    """Make the device ready for I/O.

    """
    pass

  def Close(self):
    """Notifies that the device will no longer be used for I/O.

    """
    pass

  def Grow(self, amount, dryrun, backingstore):
    """Grow the logical volume.

    """
    base.ThrowError("Grow is not supported for PersistentBlockDev storage")


class RADOSBlockDevice(base.BlockDev):
  """A RADOS Block Device (rbd).

  This class implements the RADOS Block Device for the backend. You need
  the rbd kernel driver, the RADOS Tools and a working RADOS cluster for
  this to be functional.

  """
  def __init__(self, unique_id, children, size, params):
    """Attaches to an rbd device.

    """
    super(RADOSBlockDevice, self).__init__(unique_id, children, size, params)
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise ValueError("Invalid configuration data %s" % str(unique_id))

    self.driver, self.rbd_name = unique_id

    self.major = self.minor = None
    self.Attach()

  @classmethod
  def Create(cls, unique_id, children, size, params, excl_stor):
    """Create a new rbd device.

    Provision a new rbd volume inside a RADOS pool.

    """
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise errors.ProgrammerError("Invalid configuration data %s" %
                                   str(unique_id))
    if excl_stor:
      raise errors.ProgrammerError("RBD device requested with"
                                   " exclusive_storage")
    rbd_pool = params[constants.LDP_POOL]
    rbd_name = unique_id[1]

    # Provision a new rbd volume (Image) inside the RADOS cluster.
    cmd = [constants.RBD_CMD, "create", "-p", rbd_pool,
           rbd_name, "--size", "%s" % size]
    result = utils.RunCmd(cmd)
    if result.failed:
      base.ThrowError("rbd creation failed (%s): %s",
                      result.fail_reason, result.output)

    return RADOSBlockDevice(unique_id, children, size, params)

  def Remove(self):
    """Remove the rbd device.

    """
    rbd_pool = self.params[constants.LDP_POOL]
    rbd_name = self.unique_id[1]

    if not self.minor and not self.Attach():
      # The rbd device doesn't exist.
      return

    # First shutdown the device (remove mappings).
    self.Shutdown()

    # Remove the actual Volume (Image) from the RADOS cluster.
    cmd = [constants.RBD_CMD, "rm", "-p", rbd_pool, rbd_name]
    result = utils.RunCmd(cmd)
    if result.failed:
      base.ThrowError("Can't remove Volume from cluster with rbd rm: %s - %s",
                      result.fail_reason, result.output)

  def Rename(self, new_id):
    """Rename this device.

    """
    pass

  def Attach(self):
    """Attach to an existing rbd device.

    This method maps the rbd volume that matches our name with
    an rbd device and then attaches to this device.

    """
    self.attached = False

    # Map the rbd volume to a block device under /dev
    self.dev_path = self._MapVolumeToBlockdev(self.unique_id)

    try:
      st = os.stat(self.dev_path)
    except OSError, err:
      logging.error("Error stat()'ing %s: %s", self.dev_path, str(err))
      return False

    if not stat.S_ISBLK(st.st_mode):
      logging.error("%s is not a block device", self.dev_path)
      return False

    self.major = os.major(st.st_rdev)
    self.minor = os.minor(st.st_rdev)
    self.attached = True

    return True

  def _MapVolumeToBlockdev(self, unique_id):
    """Maps existing rbd volumes to block devices.

    This method should be idempotent if the mapping already exists.

    @rtype: string
    @return: the block device path that corresponds to the volume

    """
    pool = self.params[constants.LDP_POOL]
    name = unique_id[1]

    # Check if the mapping already exists.
    rbd_dev = self._VolumeToBlockdev(pool, name)
    if rbd_dev:
      # The mapping exists. Return it.
      return rbd_dev

    # The mapping doesn't exist. Create it.
    map_cmd = [constants.RBD_CMD, "map", "-p", pool, name]
    result = utils.RunCmd(map_cmd)
    if result.failed:
      base.ThrowError("rbd map failed (%s): %s",
                      result.fail_reason, result.output)

    # Find the corresponding rbd device.
    rbd_dev = self._VolumeToBlockdev(pool, name)
    if not rbd_dev:
      base.ThrowError("rbd map succeeded, but could not find the rbd block"
                      " device in output of showmapped, for volume: %s", name)

    # The device was successfully mapped. Return it.
    return rbd_dev

  @classmethod
  def _VolumeToBlockdev(cls, pool, volume_name):
    """Do the 'volume name'-to-'rbd block device' resolving.

    @type pool: string
    @param pool: RADOS pool to use
    @type volume_name: string
    @param volume_name: the name of the volume whose device we search for
    @rtype: string or None
    @return: block device path if the volume is mapped, else None

    """
    try:
      # Newer versions of the rbd tool support json output formatting. Use it
      # if available.
      showmap_cmd = [
        constants.RBD_CMD,
        "showmapped",
        "-p",
        pool,
        "--format",
        "json"
        ]
      result = utils.RunCmd(showmap_cmd)
      if result.failed:
        logging.error("rbd JSON output formatting returned error (%s): %s,"
                      "falling back to plain output parsing",
                      result.fail_reason, result.output)
        raise RbdShowmappedJsonError

      return cls._ParseRbdShowmappedJson(result.output, volume_name)
    except RbdShowmappedJsonError:
      # For older versions of rbd, we have to parse the plain / text output
      # manually.
      showmap_cmd = [constants.RBD_CMD, "showmapped", "-p", pool]
      result = utils.RunCmd(showmap_cmd)
      if result.failed:
        base.ThrowError("rbd showmapped failed (%s): %s",
                        result.fail_reason, result.output)

      return cls._ParseRbdShowmappedPlain(result.output, volume_name)

  @staticmethod
  def _ParseRbdShowmappedJson(output, volume_name):
    """Parse the json output of `rbd showmapped'.

    This method parses the json output of `rbd showmapped' and returns the rbd
    block device path (e.g. /dev/rbd0) that matches the given rbd volume.

    @type output: string
    @param output: the json output of `rbd showmapped'
    @type volume_name: string
    @param volume_name: the name of the volume whose device we search for
    @rtype: string or None
    @return: block device path if the volume is mapped, else None

    """
    try:
      devices = serializer.LoadJson(output)
    except ValueError, err:
      base.ThrowError("Unable to parse JSON data: %s" % err)

    rbd_dev = None
    for d in devices.values(): # pylint: disable=E1103
      try:
        name = d["name"]
      except KeyError:
        base.ThrowError("'name' key missing from json object %s", devices)

      if name == volume_name:
        if rbd_dev is not None:
          base.ThrowError("rbd volume %s is mapped more than once", volume_name)

        rbd_dev = d["device"]

    return rbd_dev

  @staticmethod
  def _ParseRbdShowmappedPlain(output, volume_name):
    """Parse the (plain / text) output of `rbd showmapped'.

    This method parses the output of `rbd showmapped' and returns
    the rbd block device path (e.g. /dev/rbd0) that matches the
    given rbd volume.

    @type output: string
    @param output: the plain text output of `rbd showmapped'
    @type volume_name: string
    @param volume_name: the name of the volume whose device we search for
    @rtype: string or None
    @return: block device path if the volume is mapped, else None

    """
    allfields = 5
    volumefield = 2
    devicefield = 4

    lines = output.splitlines()

    # Try parsing the new output format (ceph >= 0.55).
    splitted_lines = map(lambda l: l.split(), lines)

    # Check for empty output.
    if not splitted_lines:
      return None

    # Check showmapped output, to determine number of fields.
    field_cnt = len(splitted_lines[0])
    if field_cnt != allfields:
      # Parsing the new format failed. Fallback to parsing the old output
      # format (< 0.55).
      splitted_lines = map(lambda l: l.split("\t"), lines)
      if field_cnt != allfields:
        base.ThrowError("Cannot parse rbd showmapped output expected %s fields,"
                        " found %s", allfields, field_cnt)

    matched_lines = \
      filter(lambda l: len(l) == allfields and l[volumefield] == volume_name,
             splitted_lines)

    if len(matched_lines) > 1:
      base.ThrowError("rbd volume %s mapped more than once", volume_name)

    if matched_lines:
      # rbd block device found. Return it.
      rbd_dev = matched_lines[0][devicefield]
      return rbd_dev

    # The given volume is not mapped.
    return None

  def Assemble(self):
    """Assemble the device.

    """
    pass

  def Shutdown(self):
    """Shutdown the device.

    """
    if not self.minor and not self.Attach():
      # The rbd device doesn't exist.
      return

    # Unmap the block device from the Volume.
    self._UnmapVolumeFromBlockdev(self.unique_id)

    self.minor = None
    self.dev_path = None

  def _UnmapVolumeFromBlockdev(self, unique_id):
    """Unmaps the rbd device from the Volume it is mapped.

    Unmaps the rbd device from the Volume it was previously mapped to.
    This method should be idempotent if the Volume isn't mapped.

    """
    pool = self.params[constants.LDP_POOL]
    name = unique_id[1]

    # Check if the mapping already exists.
    rbd_dev = self._VolumeToBlockdev(pool, name)

    if rbd_dev:
      # The mapping exists. Unmap the rbd device.
      unmap_cmd = [constants.RBD_CMD, "unmap", "%s" % rbd_dev]
      result = utils.RunCmd(unmap_cmd)
      if result.failed:
        base.ThrowError("rbd unmap failed (%s): %s",
                        result.fail_reason, result.output)

  def Open(self, force=False):
    """Make the device ready for I/O.

    """
    pass

  def Close(self):
    """Notifies that the device will no longer be used for I/O.

    """
    pass

  def Grow(self, amount, dryrun, backingstore):
    """Grow the Volume.

    @type amount: integer
    @param amount: the amount (in mebibytes) to grow with
    @type dryrun: boolean
    @param dryrun: whether to execute the operation in simulation mode
        only, without actually increasing the size

    """
    if not backingstore:
      return
    if not self.Attach():
      base.ThrowError("Can't attach to rbd device during Grow()")

    if dryrun:
      # the rbd tool does not support dry runs of resize operations.
      # Since rbd volumes are thinly provisioned, we assume
      # there is always enough free space for the operation.
      return

    rbd_pool = self.params[constants.LDP_POOL]
    rbd_name = self.unique_id[1]
    new_size = self.size + amount

    # Resize the rbd volume (Image) inside the RADOS cluster.
    cmd = [constants.RBD_CMD, "resize", "-p", rbd_pool,
           rbd_name, "--size", "%s" % new_size]
    result = utils.RunCmd(cmd)
    if result.failed:
      base.ThrowError("rbd resize failed (%s): %s",
                      result.fail_reason, result.output)


class ExtStorageDevice(base.BlockDev):
  """A block device provided by an ExtStorage Provider.

  This class implements the External Storage Interface, which means
  handling of the externally provided block devices.

  """
  def __init__(self, unique_id, children, size, params):
    """Attaches to an extstorage block device.

    """
    super(ExtStorageDevice, self).__init__(unique_id, children, size, params)
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise ValueError("Invalid configuration data %s" % str(unique_id))

    self.driver, self.vol_name = unique_id
    self.ext_params = params

    self.major = self.minor = None
    self.Attach()

  @classmethod
  def Create(cls, unique_id, children, size, params, excl_stor):
    """Create a new extstorage device.

    Provision a new volume using an extstorage provider, which will
    then be mapped to a block device.

    """
    if not isinstance(unique_id, (tuple, list)) or len(unique_id) != 2:
      raise errors.ProgrammerError("Invalid configuration data %s" %
                                   str(unique_id))
    if excl_stor:
      raise errors.ProgrammerError("extstorage device requested with"
                                   " exclusive_storage")

    # Call the External Storage's create script,
    # to provision a new Volume inside the External Storage
    _ExtStorageAction(constants.ES_ACTION_CREATE, unique_id,
                      params, str(size))

    return ExtStorageDevice(unique_id, children, size, params)

  def Remove(self):
    """Remove the extstorage device.

    """
    if not self.minor and not self.Attach():
      # The extstorage device doesn't exist.
      return

    # First shutdown the device (remove mappings).
    self.Shutdown()

    # Call the External Storage's remove script,
    # to remove the Volume from the External Storage
    _ExtStorageAction(constants.ES_ACTION_REMOVE, self.unique_id,
                      self.ext_params)

  def Rename(self, new_id):
    """Rename this device.

    """
    pass

  def Attach(self):
    """Attach to an existing extstorage device.

    This method maps the extstorage volume that matches our name with
    a corresponding block device and then attaches to this device.

    """
    self.attached = False

    # Call the External Storage's attach script,
    # to attach an existing Volume to a block device under /dev
    self.dev_path = _ExtStorageAction(constants.ES_ACTION_ATTACH,
                                      self.unique_id, self.ext_params)

    try:
      st = os.stat(self.dev_path)
    except OSError, err:
      logging.error("Error stat()'ing %s: %s", self.dev_path, str(err))
      return False

    if not stat.S_ISBLK(st.st_mode):
      logging.error("%s is not a block device", self.dev_path)
      return False

    self.major = os.major(st.st_rdev)
    self.minor = os.minor(st.st_rdev)
    self.attached = True

    return True

  def Assemble(self):
    """Assemble the device.

    """
    pass

  def Shutdown(self):
    """Shutdown the device.

    """
    if not self.minor and not self.Attach():
      # The extstorage device doesn't exist.
      return

    # Call the External Storage's detach script,
    # to detach an existing Volume from it's block device under /dev
    _ExtStorageAction(constants.ES_ACTION_DETACH, self.unique_id,
                      self.ext_params)

    self.minor = None
    self.dev_path = None

  def Open(self, force=False):
    """Make the device ready for I/O.

    """
    pass

  def Close(self):
    """Notifies that the device will no longer be used for I/O.

    """
    pass

  def Grow(self, amount, dryrun, backingstore):
    """Grow the Volume.

    @type amount: integer
    @param amount: the amount (in mebibytes) to grow with
    @type dryrun: boolean
    @param dryrun: whether to execute the operation in simulation mode
        only, without actually increasing the size

    """
    if not backingstore:
      return
    if not self.Attach():
      base.ThrowError("Can't attach to extstorage device during Grow()")

    if dryrun:
      # we do not support dry runs of resize operations for now.
      return

    new_size = self.size + amount

    # Call the External Storage's grow script,
    # to grow an existing Volume inside the External Storage
    _ExtStorageAction(constants.ES_ACTION_GROW, self.unique_id,
                      self.ext_params, str(self.size), grow=str(new_size))

  def SetInfo(self, text):
    """Update metadata with info 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]

    # Call the External Storage's setinfo script,
    # to set metadata for an existing Volume inside the External Storage
    _ExtStorageAction(constants.ES_ACTION_SETINFO, self.unique_id,
                      self.ext_params, metadata=text)


def _ExtStorageAction(action, unique_id, ext_params,
                      size=None, grow=None, metadata=None):
  """Take an External Storage action.

  Take an External Storage action concerning or affecting
  a specific Volume inside the External Storage.

  @type action: string
  @param action: which action to perform. One of:
                 create / remove / grow / attach / detach
  @type unique_id: tuple (driver, vol_name)
  @param unique_id: a tuple containing the type of ExtStorage (driver)
                    and the Volume name
  @type ext_params: dict
  @param ext_params: ExtStorage parameters
  @type size: integer
  @param size: the size of the Volume in mebibytes
  @type grow: integer
  @param grow: the new size in mebibytes (after grow)
  @type metadata: string
  @param metadata: metadata info of the Volume, for use by the provider
  @rtype: None or a block device path (during attach)

  """
  driver, vol_name = unique_id

  # Create an External Storage instance of type `driver'
  status, inst_es = ExtStorageFromDisk(driver)
  if not status:
    base.ThrowError("%s" % inst_es)

  # Create the basic environment for the driver's scripts
  create_env = _ExtStorageEnvironment(unique_id, ext_params, size,
                                      grow, metadata)

  # Do not use log file for action `attach' as we need
  # to get the output from RunResult
  # TODO: find a way to have a log file for attach too
  logfile = None
  if action is not constants.ES_ACTION_ATTACH:
    logfile = _VolumeLogName(action, driver, vol_name)

  # Make sure the given action results in a valid script
  if action not in constants.ES_SCRIPTS:
    base.ThrowError("Action '%s' doesn't result in a valid ExtStorage script" %
                    action)

  # Find out which external script to run according the given action
  script_name = action + "_script"
  script = getattr(inst_es, script_name)

  # Run the external script
  result = utils.RunCmd([script], env=create_env,
                        cwd=inst_es.path, output=logfile,)
  if result.failed:
    logging.error("External storage's %s command '%s' returned"
                  " error: %s, logfile: %s, output: %s",
                  action, result.cmd, result.fail_reason,
                  logfile, result.output)

    # If logfile is 'None' (during attach), it breaks TailFile
    # TODO: have a log file for attach too
    if action is not constants.ES_ACTION_ATTACH:
      lines = [utils.SafeEncode(val)
               for val in utils.TailFile(logfile, lines=20)]
    else:
      lines = result.output[-20:]

    base.ThrowError("External storage's %s script failed (%s), last"
                    " lines of output:\n%s",
                    action, result.fail_reason, "\n".join(lines))

  if action == constants.ES_ACTION_ATTACH:
    return result.stdout


def ExtStorageFromDisk(name, base_dir=None):
  """Create an ExtStorage instance from disk.

  This function will return an ExtStorage instance
  if the given name is a valid ExtStorage name.

  @type base_dir: string
  @keyword base_dir: Base directory containing ExtStorage installations.
                     Defaults to a search in all the ES_SEARCH_PATH dirs.
  @rtype: tuple
  @return: True and the ExtStorage instance if we find a valid one, or
      False and the diagnose message on error

  """
  if base_dir is None:
    es_base_dir = pathutils.ES_SEARCH_PATH
  else:
    es_base_dir = [base_dir]

  es_dir = utils.FindFile(name, es_base_dir, os.path.isdir)

  if es_dir is None:
    return False, ("Directory for External Storage Provider %s not"
                   " found in search path" % name)

  # ES Files dictionary, we will populate it with the absolute path
  # names; if the value is True, then it is a required file, otherwise
  # an optional one
  es_files = dict.fromkeys(constants.ES_SCRIPTS, True)

  es_files[constants.ES_PARAMETERS_FILE] = True

  for (filename, _) in es_files.items():
    es_files[filename] = utils.PathJoin(es_dir, filename)

    try:
      st = os.stat(es_files[filename])
    except EnvironmentError, err:
      return False, ("File '%s' under path '%s' is missing (%s)" %
                     (filename, es_dir, utils.ErrnoOrStr(err)))

    if not stat.S_ISREG(stat.S_IFMT(st.st_mode)):
      return False, ("File '%s' under path '%s' is not a regular file" %
                     (filename, es_dir))

    if filename in constants.ES_SCRIPTS:
      if stat.S_IMODE(st.st_mode) & stat.S_IXUSR != stat.S_IXUSR:
        return False, ("File '%s' under path '%s' is not executable" %
                       (filename, es_dir))

  parameters = []
  if constants.ES_PARAMETERS_FILE in es_files:
    parameters_file = es_files[constants.ES_PARAMETERS_FILE]
    try:
      parameters = utils.ReadFile(parameters_file).splitlines()
    except EnvironmentError, err:
      return False, ("Error while reading the EXT parameters file at %s: %s" %
                     (parameters_file, utils.ErrnoOrStr(err)))
    parameters = [v.split(None, 1) for v in parameters]

  es_obj = \
    objects.ExtStorage(name=name, path=es_dir,
                       create_script=es_files[constants.ES_SCRIPT_CREATE],
                       remove_script=es_files[constants.ES_SCRIPT_REMOVE],
                       grow_script=es_files[constants.ES_SCRIPT_GROW],
                       attach_script=es_files[constants.ES_SCRIPT_ATTACH],
                       detach_script=es_files[constants.ES_SCRIPT_DETACH],
                       setinfo_script=es_files[constants.ES_SCRIPT_SETINFO],
                       verify_script=es_files[constants.ES_SCRIPT_VERIFY],
                       supported_parameters=parameters)
  return True, es_obj


def _ExtStorageEnvironment(unique_id, ext_params,
                           size=None, grow=None, metadata=None):
  """Calculate the environment for an External Storage script.

  @type unique_id: tuple (driver, vol_name)
  @param unique_id: ExtStorage pool and name of the Volume
  @type ext_params: dict
  @param ext_params: the EXT parameters
  @type size: string
  @param size: size of the Volume (in mebibytes)
  @type grow: string
  @param grow: new size of Volume after grow (in mebibytes)
  @type metadata: string
  @param metadata: metadata info of the Volume
  @rtype: dict
  @return: dict of environment variables

  """
  vol_name = unique_id[1]

  result = {}
  result["VOL_NAME"] = vol_name

  # EXT params
  for pname, pvalue in ext_params.items():
    result["EXTP_%s" % pname.upper()] = str(pvalue)

  if size is not None:
    result["VOL_SIZE"] = size

  if grow is not None:
    result["VOL_NEW_SIZE"] = grow

  if metadata is not None:
    result["VOL_METADATA"] = metadata

  return result


def _VolumeLogName(kind, es_name, volume):
  """Compute the ExtStorage log filename for a given Volume and operation.

  @type kind: string
  @param kind: the operation type (e.g. create, remove etc.)
  @type es_name: string
  @param es_name: the ExtStorage name
  @type volume: string
  @param volume: the name of the Volume inside the External Storage

  """
  # Check if the extstorage log dir is a valid dir
  if not os.path.isdir(pathutils.LOG_ES_DIR):
    base.ThrowError("Cannot find log directory: %s", pathutils.LOG_ES_DIR)

  # TODO: Use tempfile.mkstemp to create unique filename
  basename = ("%s-%s-%s-%s.log" %
              (kind, es_name, volume, utils.TimestampForFilename()))
  return utils.PathJoin(pathutils.LOG_ES_DIR, basename)


DEV_MAP = {
  constants.LD_LV: LogicalVolume,
  constants.LD_DRBD8: drbd.DRBD8Dev,
  constants.LD_BLOCKDEV: PersistentBlockDevice,
  constants.LD_RBD: RADOSBlockDevice,
  constants.LD_EXT: ExtStorageDevice,
  }

if constants.ENABLE_FILE_STORAGE or constants.ENABLE_SHARED_FILE_STORAGE:
  DEV_MAP[constants.LD_FILE] = FileStorage


def _VerifyDiskType(dev_type):
  if dev_type not in DEV_MAP:
    raise errors.ProgrammerError("Invalid block device type '%s'" % dev_type)


def _VerifyDiskParams(disk):
  """Verifies if all disk parameters are set.

  """
  missing = set(constants.DISK_LD_DEFAULTS[disk.dev_type]) - set(disk.params)
  if missing:
    raise errors.ProgrammerError("Block device is missing disk parameters: %s" %
                                 missing)


def FindDevice(disk, 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.

  @type disk: L{objects.Disk}
  @param disk: the disk object to find
  @type children: list of L{bdev.BlockDev}
  @param children: the list of block devices that are children of the device
                  represented by the disk parameter

  """
  _VerifyDiskType(disk.dev_type)
  device = DEV_MAP[disk.dev_type](disk.physical_id, children, disk.size,
                                  disk.params)
  if not device.attached:
    return None
  return device


def Assemble(disk, 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.

  @type disk: L{objects.Disk}
  @param disk: the disk object to assemble
  @type children: list of L{bdev.BlockDev}
  @param children: the list of block devices that are children of the device
                  represented by the disk parameter

  """
  _VerifyDiskType(disk.dev_type)
  _VerifyDiskParams(disk)
  device = DEV_MAP[disk.dev_type](disk.physical_id, children, disk.size,
                                  disk.params)
  device.Assemble()
  return device


def Create(disk, children, excl_stor):
  """Create a device.

  @type disk: L{objects.Disk}
  @param disk: the disk object to create
  @type children: list of L{bdev.BlockDev}
  @param children: the list of block devices that are children of the device
                  represented by the disk parameter
  @type excl_stor: boolean
  @param excl_stor: Whether exclusive_storage is active

  """
  _VerifyDiskType(disk.dev_type)
  _VerifyDiskParams(disk)
  device = DEV_MAP[disk.dev_type].Create(disk.physical_id, children, disk.size,
                                         disk.params, excl_stor)
  return device