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"""Utility functions for LVM.

"""

from ganeti import constants

def CheckVolumeGroupSize(vglist, vgname, minsize):

  """Checks if the volume group list is valid.

  The function will check if a given volume group is in the list of

  volume groups and has a minimum size.

  @type vglist: dict

  @param vglist: dictionary of volume group names and their size

  @type vgname: str

  @param vgname: the volume group we should check

  @type minsize: int

  @param minsize: the minimum size we accept

  @rtype: None or str

  @return: None for success, otherwise the error message

  """

  vgsize = vglist.get(vgname, None)

  if vgsize is None:

    return "volume group '%s' missing" % vgname

  elif vgsize < minsize:

    return ("volume group '%s' too small (%s MiB required, %d MiB found)" %

            (vgname, minsize, vgsize))

  return None

def LvmExclusiveCheckNodePvs(pvs_info):

  """Check consistency of PV sizes in a node for exclusive storage.

  @type pvs_info: list

  @param pvs_info: list of L{LvmPvInfo} objects

  @rtype: list

  @return: A list of error strings described the violation found, or an empty

      list if everything is ok

  """

  errmsgs = []

  sizes = [pv.size for pv in pvs_info]

  # The sizes of PVs must be the same (tolerance is constants.PART_MARGIN)

  small = min(sizes)

  big = max(sizes)

  if LvmExclusiveTestBadPvSizes(small, big):

    m = ("Sizes of PVs are too different: min=%d max=%d" % (small, big))

    errmsgs.append(m)

  return errmsgs

def LvmExclusiveTestBadPvSizes(small, big):

  """Test if the given PV sizes are permitted with exclusive storage.

  @param small: size of the smallest PV

  @param big: size of the biggest PV

  @return: True when the given sizes are bad, False otherwise

  """

  # Test whether no X exists such that:

  #   small >= X * (1 - constants.PART_MARGIN)  and

  #   big <= X * (1 + constants.PART_MARGIN)

  return (small * (1 + constants.PART_MARGIN) <

          big * (1 - constants.PART_MARGIN))