[ganeti-local] / lib / objects.py

#
#

# 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.


"""Transportable objects for Ganeti.

This module provides small, mostly data-only objects which are safe to
pass to and from external parties.

"""


import ConfigParser
import re
import copy
from cStringIO import StringIO

from ganeti import errors
from ganeti import constants


__all__ = ["ConfigObject", "ConfigData", "NIC", "Disk", "Instance",
           "OS", "Node", "Cluster", "FillDict"]

def FillDict(defaults_dict, custom_dict):
    """Basic function to apply settings on top a default dict.

    @type defaults_dict: dict
    @param defaults_dict: dictionary holding the default values
    @type custom_dict: dict
    @param custom_dict: dictionary holding customized value
    @rtype: dict
    @return: dict with the 'full' values

    """
    ret_dict = copy.deepcopy(defaults_dict)
    ret_dict.update(custom_dict)
    return ret_dict


def UpgradeGroupedParams(target, defaults):
  """Update all groups for the target parameter.

  @type target: dict of dicts
  @param target: {group: {parameter: value}}
  @type defaults: dict
  @param defaults: default parameter values

  """
  if target is None:
    target = {constants.PP_DEFAULT: defaults}
  else:
    for group in target:
      target[group] = FillDict(defaults, target[group])
  return target


class ConfigObject(object):
  """A generic config object.

  It has the following properties:

    - provides somewhat safe recursive unpickling and pickling for its classes
    - unset attributes which are defined in slots are always returned
      as None instead of raising an error

  Classes derived from this must always declare __slots__ (we use many
  config objects and the memory reduction is useful)

  """
  __slots__ = []

  def __init__(self, **kwargs):
    for k, v in kwargs.iteritems():
      setattr(self, k, v)
    self.UpgradeConfig()

  def __getattr__(self, name):
    if name not in self.__slots__:
      raise AttributeError("Invalid object attribute %s.%s" %
                           (type(self).__name__, name))
    return None

  def __setitem__(self, key, value):
    if key not in self.__slots__:
      raise KeyError(key)
    setattr(self, key, value)

  def __getstate__(self):
    state = {}
    for name in self.__slots__:
      if hasattr(self, name):
        state[name] = getattr(self, name)
    return state

  def __setstate__(self, state):
    for name in state:
      if name in self.__slots__:
        setattr(self, name, state[name])

  def ToDict(self):
    """Convert to a dict holding only standard python types.

    The generic routine just dumps all of this object's attributes in
    a dict. It does not work if the class has children who are
    ConfigObjects themselves (e.g. the nics list in an Instance), in
    which case the object should subclass the function in order to
    make sure all objects returned are only standard python types.

    """
    return dict([(k, getattr(self, k, None)) for k in self.__slots__])

  @classmethod
  def FromDict(cls, val):
    """Create an object from a dictionary.

    This generic routine takes a dict, instantiates a new instance of
    the given class, and sets attributes based on the dict content.

    As for `ToDict`, this does not work if the class has children
    who are ConfigObjects themselves (e.g. the nics list in an
    Instance), in which case the object should subclass the function
    and alter the objects.

    """
    if not isinstance(val, dict):
      raise errors.ConfigurationError("Invalid object passed to FromDict:"
                                      " expected dict, got %s" % type(val))
    val_str = dict([(str(k), v) for k, v in val.iteritems()])
    obj = cls(**val_str)
    return obj

  @staticmethod
  def _ContainerToDicts(container):
    """Convert the elements of a container to standard python types.

    This method converts a container with elements derived from
    ConfigData to standard python types. If the container is a dict,
    we don't touch the keys, only the values.

    """
    if isinstance(container, dict):
      ret = dict([(k, v.ToDict()) for k, v in container.iteritems()])
    elif isinstance(container, (list, tuple, set, frozenset)):
      ret = [elem.ToDict() for elem in container]
    else:
      raise TypeError("Invalid type %s passed to _ContainerToDicts" %
                      type(container))
    return ret

  @staticmethod
  def _ContainerFromDicts(source, c_type, e_type):
    """Convert a container from standard python types.

    This method converts a container with standard python types to
    ConfigData objects. If the container is a dict, we don't touch the
    keys, only the values.

    """
    if not isinstance(c_type, type):
      raise TypeError("Container type %s passed to _ContainerFromDicts is"
                      " not a type" % type(c_type))
    if c_type is dict:
      ret = dict([(k, e_type.FromDict(v)) for k, v in source.iteritems()])
    elif c_type in (list, tuple, set, frozenset):
      ret = c_type([e_type.FromDict(elem) for elem in source])
    else:
      raise TypeError("Invalid container type %s passed to"
                      " _ContainerFromDicts" % c_type)
    return ret

  def __repr__(self):
    """Implement __repr__ for ConfigObjects."""
    return repr(self.ToDict())

  def UpgradeConfig(self):
    """Fill defaults for missing configuration values.

    This method will be called at object init time, and its implementation will
    be object dependent.

    """
    pass


class TaggableObject(ConfigObject):
  """An generic class supporting tags.

  """
  __slots__ = ConfigObject.__slots__ + ["tags"]

  @staticmethod
  def ValidateTag(tag):
    """Check if a tag is valid.

    If the tag is invalid, an errors.TagError will be raised. The
    function has no return value.

    """
    if not isinstance(tag, basestring):
      raise errors.TagError("Invalid tag type (not a string)")
    if len(tag) > constants.MAX_TAG_LEN:
      raise errors.TagError("Tag too long (>%d characters)" %
                            constants.MAX_TAG_LEN)
    if not tag:
      raise errors.TagError("Tags cannot be empty")
    if not re.match("^[\w.+*/:-]+$", tag):
      raise errors.TagError("Tag contains invalid characters")

  def GetTags(self):
    """Return the tags list.

    """
    tags = getattr(self, "tags", None)
    if tags is None:
      tags = self.tags = set()
    return tags

  def AddTag(self, tag):
    """Add a new tag.

    """
    self.ValidateTag(tag)
    tags = self.GetTags()
    if len(tags) >= constants.MAX_TAGS_PER_OBJ:
      raise errors.TagError("Too many tags")
    self.GetTags().add(tag)

  def RemoveTag(self, tag):
    """Remove a tag.

    """
    self.ValidateTag(tag)
    tags = self.GetTags()
    try:
      tags.remove(tag)
    except KeyError:
      raise errors.TagError("Tag not found")

  def ToDict(self):
    """Taggable-object-specific conversion to standard python types.

    This replaces the tags set with a list.

    """
    bo = super(TaggableObject, self).ToDict()

    tags = bo.get("tags", None)
    if isinstance(tags, set):
      bo["tags"] = list(tags)
    return bo

  @classmethod
  def FromDict(cls, val):
    """Custom function for instances.

    """
    obj = super(TaggableObject, cls).FromDict(val)
    if hasattr(obj, "tags") and isinstance(obj.tags, list):
      obj.tags = set(obj.tags)
    return obj


class ConfigData(ConfigObject):
  """Top-level config object."""
  __slots__ = ["version", "cluster", "nodes", "instances", "serial_no"]

  def ToDict(self):
    """Custom function for top-level config data.

    This just replaces the list of instances, nodes and the cluster
    with standard python types.

    """
    mydict = super(ConfigData, self).ToDict()
    mydict["cluster"] = mydict["cluster"].ToDict()
    for key in "nodes", "instances":
      mydict[key] = self._ContainerToDicts(mydict[key])

    return mydict

  @classmethod
  def FromDict(cls, val):
    """Custom function for top-level config data

    """
    obj = super(ConfigData, cls).FromDict(val)
    obj.cluster = Cluster.FromDict(obj.cluster)
    obj.nodes = cls._ContainerFromDicts(obj.nodes, dict, Node)
    obj.instances = cls._ContainerFromDicts(obj.instances, dict, Instance)
    return obj


class NIC(ConfigObject):
  """Config object representing a network card."""
  __slots__ = ["mac", "ip", "bridge", "nicparams"]

  @classmethod
  def CheckParameterSyntax(cls, nicparams):
    """Check the given parameters for validity.

    @type nicparams:  dict
    @param nicparams: dictionary with parameter names/value
    @raise errors.ConfigurationError: when a parameter is not valid

    """
    if nicparams[constants.NIC_MODE] not in constants.NIC_VALID_MODES:
      err = "Invalid nic mode: %s" % nicparams[constants.NIC_MODE]
      raise errors.ConfigurationError(err)

    if (nicparams[constants.NIC_MODE] is constants.NIC_MODE_BRIDGED and
        not nicparams[constants.NIC_LINK]):
      err = "Missing bridged nic link"
      raise errors.ConfigurationError(err)

  def UpgradeConfig(self):
    """Fill defaults for missing configuration values.

    """
    if self.nicparams is None:
      self.nicparams = {}
      if self.bridge is not None:
        self.nicparams[constants.NIC_MODE] = constants.NIC_MODE_BRIDGED
        self.nicparams[constants.NIC_LINK] = self.bridge
    # bridge is no longer used it 2.1. The slot is left there to support
    # upgrading, but will be removed in 2.2
    if self.bridge is not None:
      self.bridge = None


class Disk(ConfigObject):
  """Config object representing a block device."""
  __slots__ = ["dev_type", "logical_id", "physical_id",
               "children", "iv_name", "size", "mode"]

  def CreateOnSecondary(self):
    """Test if this device needs to be created on a secondary node."""
    return self.dev_type in (constants.LD_DRBD8, constants.LD_LV)

  def AssembleOnSecondary(self):
    """Test if this device needs to be assembled on a secondary node."""
    return self.dev_type in (constants.LD_DRBD8, constants.LD_LV)

  def OpenOnSecondary(self):
    """Test if this device needs to be opened on a secondary node."""
    return self.dev_type in (constants.LD_LV,)

  def StaticDevPath(self):
    """Return the device path if this device type has a static one.

    Some devices (LVM for example) live always at the same /dev/ path,
    irrespective of their status. For such devices, we return this
    path, for others we return None.

    """
    if self.dev_type == constants.LD_LV:
      return "/dev/%s/%s" % (self.logical_id[0], self.logical_id[1])
    return None

  def ChildrenNeeded(self):
    """Compute the needed number of children for activation.

    This method will return either -1 (all children) or a positive
    number denoting the minimum number of children needed for
    activation (only mirrored devices will usually return >=0).

    Currently, only DRBD8 supports diskless activation (therefore we
    return 0), for all other we keep the previous semantics and return
    -1.

    """
    if self.dev_type == constants.LD_DRBD8:
      return 0
    return -1

  def GetNodes(self, node):
    """This function returns the nodes this device lives on.

    Given the node on which the parent of the device lives on (or, in
    case of a top-level device, the primary node of the devices'
    instance), this function will return a list of nodes on which this
    devices needs to (or can) be assembled.

    """
    if self.dev_type in [constants.LD_LV, constants.LD_FILE]:
      result = [node]
    elif self.dev_type in constants.LDS_DRBD:
      result = [self.logical_id[0], self.logical_id[1]]
      if node not in result:
        raise errors.ConfigurationError("DRBD device passed unknown node")
    else:
      raise errors.ProgrammerError("Unhandled device type %s" % self.dev_type)
    return result

  def ComputeNodeTree(self, parent_node):
    """Compute the node/disk tree for this disk and its children.

    This method, given the node on which the parent disk lives, will
    return the list of all (node, disk) pairs which describe the disk
    tree in the most compact way. For example, a drbd/lvm stack
    will be returned as (primary_node, drbd) and (secondary_node, drbd)
    which represents all the top-level devices on the nodes.

    """
    my_nodes = self.GetNodes(parent_node)
    result = [(node, self) for node in my_nodes]
    if not self.children:
      # leaf device
      return result
    for node in my_nodes:
      for child in self.children:
        child_result = child.ComputeNodeTree(node)
        if len(child_result) == 1:
          # child (and all its descendants) is simple, doesn't split
          # over multiple hosts, so we don't need to describe it, our
          # own entry for this node describes it completely
          continue
        else:
          # check if child nodes differ from my nodes; note that
          # subdisk can differ from the child itself, and be instead
          # one of its descendants
          for subnode, subdisk in child_result:
            if subnode not in my_nodes:
              result.append((subnode, subdisk))
            # otherwise child is under our own node, so we ignore this
            # entry (but probably the other results in the list will
            # be different)
    return result

  def RecordGrow(self, amount):
    """Update the size of this disk after growth.

    This method recurses over the disks's children and updates their
    size correspondigly. The method needs to be kept in sync with the
    actual algorithms from bdev.

    """
    if self.dev_type == constants.LD_LV:
      self.size += amount
    elif self.dev_type == constants.LD_DRBD8:
      if self.children:
        self.children[0].RecordGrow(amount)
      self.size += amount
    else:
      raise errors.ProgrammerError("Disk.RecordGrow called for unsupported"
                                   " disk type %s" % self.dev_type)

  def SetPhysicalID(self, target_node, nodes_ip):
    """Convert the logical ID to the physical ID.

    This is used only for drbd, which needs ip/port configuration.

    The routine descends down and updates its children also, because
    this helps when the only the top device is passed to the remote
    node.

    Arguments:
      - target_node: the node we wish to configure for
      - nodes_ip: a mapping of node name to ip

    The target_node must exist in in nodes_ip, and must be one of the
    nodes in the logical ID for each of the DRBD devices encountered
    in the disk tree.

    """
    if self.children:
      for child in self.children:
        child.SetPhysicalID(target_node, nodes_ip)

    if self.logical_id is None and self.physical_id is not None:
      return
    if self.dev_type in constants.LDS_DRBD:
      pnode, snode, port, pminor, sminor, secret = self.logical_id
      if target_node not in (pnode, snode):
        raise errors.ConfigurationError("DRBD device not knowing node %s" %
                                        target_node)
      pnode_ip = nodes_ip.get(pnode, None)
      snode_ip = nodes_ip.get(snode, None)
      if pnode_ip is None or snode_ip is None:
        raise errors.ConfigurationError("Can't find primary or secondary node"
                                        " for %s" % str(self))
      p_data = (pnode_ip, port)
      s_data = (snode_ip, port)
      if pnode == target_node:
        self.physical_id = p_data + s_data + (pminor, secret)
      else: # it must be secondary, we tested above
        self.physical_id = s_data + p_data + (sminor, secret)
    else:
      self.physical_id = self.logical_id
    return

  def ToDict(self):
    """Disk-specific conversion to standard python types.

    This replaces the children lists of objects with lists of
    standard python types.

    """
    bo = super(Disk, self).ToDict()

    for attr in ("children",):
      alist = bo.get(attr, None)
      if alist:
        bo[attr] = self._ContainerToDicts(alist)
    return bo

  @classmethod
  def FromDict(cls, val):
    """Custom function for Disks

    """
    obj = super(Disk, cls).FromDict(val)
    if obj.children:
      obj.children = cls._ContainerFromDicts(obj.children, list, Disk)
    if obj.logical_id and isinstance(obj.logical_id, list):
      obj.logical_id = tuple(obj.logical_id)
    if obj.physical_id and isinstance(obj.physical_id, list):
      obj.physical_id = tuple(obj.physical_id)
    if obj.dev_type in constants.LDS_DRBD:
      # we need a tuple of length six here
      if len(obj.logical_id) < 6:
        obj.logical_id += (None,) * (6 - len(obj.logical_id))
    return obj

  def __str__(self):
    """Custom str() formatter for disks.

    """
    if self.dev_type == constants.LD_LV:
      val =  "<LogicalVolume(/dev/%s/%s" % self.logical_id
    elif self.dev_type in constants.LDS_DRBD:
      node_a, node_b, port, minor_a, minor_b = self.logical_id[:5]
      val = "<DRBD8("
      if self.physical_id is None:
        phy = "unconfigured"
      else:
        phy = ("configured as %s:%s %s:%s" %
               (self.physical_id[0], self.physical_id[1],
                self.physical_id[2], self.physical_id[3]))

      val += ("hosts=%s/%d-%s/%d, port=%s, %s, " %
              (node_a, minor_a, node_b, minor_b, port, phy))
      if self.children and self.children.count(None) == 0:
        val += "backend=%s, metadev=%s" % (self.children[0], self.children[1])
      else:
        val += "no local storage"
    else:
      val = ("<Disk(type=%s, logical_id=%s, physical_id=%s, children=%s" %
             (self.dev_type, self.logical_id, self.physical_id, self.children))
    if self.iv_name is None:
      val += ", not visible"
    else:
      val += ", visible as /dev/%s" % self.iv_name
    if isinstance(self.size, int):
      val += ", size=%dm)>" % self.size
    else:
      val += ", size='%s')>" % (self.size,)
    return val

  def Verify(self):
    """Checks that this disk is correctly configured.

    """
    errors = []
    if self.mode not in constants.DISK_ACCESS_SET:
      errors.append("Disk access mode '%s' is invalid" % (self.mode, ))
    return errors


class Instance(TaggableObject):
  """Config object representing an instance."""
  __slots__ = TaggableObject.__slots__ + [
    "name",
    "primary_node",
    "os",
    "hypervisor",
    "hvparams",
    "beparams",
    "admin_up",
    "nics",
    "disks",
    "disk_template",
    "network_port",
    "serial_no",
    ]

  def _ComputeSecondaryNodes(self):
    """Compute the list of secondary nodes.

    This is a simple wrapper over _ComputeAllNodes.

    """
    all_nodes = set(self._ComputeAllNodes())
    all_nodes.discard(self.primary_node)
    return tuple(all_nodes)

  secondary_nodes = property(_ComputeSecondaryNodes, None, None,
                             "List of secondary nodes")

  def _ComputeAllNodes(self):
    """Compute the list of all nodes.

    Since the data is already there (in the drbd disks), keeping it as
    a separate normal attribute is redundant and if not properly
    synchronised can cause problems. Thus it's better to compute it
    dynamically.

    """
    def _Helper(nodes, device):
      """Recursively computes nodes given a top device."""
      if device.dev_type in constants.LDS_DRBD:
        nodea, nodeb = device.logical_id[:2]
        nodes.add(nodea)
        nodes.add(nodeb)
      if device.children:
        for child in device.children:
          _Helper(nodes, child)

    all_nodes = set()
    all_nodes.add(self.primary_node)
    for device in self.disks:
      _Helper(all_nodes, device)
    return tuple(all_nodes)

  all_nodes = property(_ComputeAllNodes, None, None,
                       "List of all nodes of the instance")

  def MapLVsByNode(self, lvmap=None, devs=None, node=None):
    """Provide a mapping of nodes to LVs this instance owns.

    This function figures out what logical volumes should belong on
    which nodes, recursing through a device tree.

    @param lvmap: optional dictionary to receive the
        'node' : ['lv', ...] data.

    @return: None if lvmap arg is given, otherwise, a dictionary
        of the form { 'nodename' : ['volume1', 'volume2', ...], ... }

    """
    if node == None:
      node = self.primary_node

    if lvmap is None:
      lvmap = { node : [] }
      ret = lvmap
    else:
      if not node in lvmap:
        lvmap[node] = []
      ret = None

    if not devs:
      devs = self.disks

    for dev in devs:
      if dev.dev_type == constants.LD_LV:
        lvmap[node].append(dev.logical_id[1])

      elif dev.dev_type in constants.LDS_DRBD:
        if dev.children:
          self.MapLVsByNode(lvmap, dev.children, dev.logical_id[0])
          self.MapLVsByNode(lvmap, dev.children, dev.logical_id[1])

      elif dev.children:
        self.MapLVsByNode(lvmap, dev.children, node)

    return ret

  def FindDisk(self, idx):
    """Find a disk given having a specified index.

    This is just a wrapper that does validation of the index.

    @type idx: int
    @param idx: the disk index
    @rtype: L{Disk}
    @return: the corresponding disk
    @raise errors.OpPrereqError: when the given index is not valid

    """
    try:
      idx = int(idx)
      return self.disks[idx]
    except ValueError, err:
      raise errors.OpPrereqError("Invalid disk index: '%s'" % str(err))
    except IndexError:
      raise errors.OpPrereqError("Invalid disk index: %d (instace has disks"
                                 " 0 to %d" % (idx, len(self.disks)))

  def ToDict(self):
    """Instance-specific conversion to standard python types.

    This replaces the children lists of objects with lists of standard
    python types.

    """
    bo = super(Instance, self).ToDict()

    for attr in "nics", "disks":
      alist = bo.get(attr, None)
      if alist:
        nlist = self._ContainerToDicts(alist)
      else:
        nlist = []
      bo[attr] = nlist
    return bo

  @classmethod
  def FromDict(cls, val):
    """Custom function for instances.

    """
    obj = super(Instance, cls).FromDict(val)
    obj.nics = cls._ContainerFromDicts(obj.nics, list, NIC)
    obj.disks = cls._ContainerFromDicts(obj.disks, list, Disk)
    return obj


class OS(ConfigObject):
  """Config object representing an operating system."""
  __slots__ = [
    "name",
    "path",
    "status",
    "api_versions",
    "create_script",
    "export_script",
    "import_script",
    "rename_script",
    ]

  @classmethod
  def FromInvalidOS(cls, err):
    """Create an OS from an InvalidOS error.

    This routine knows how to convert an InvalidOS error to an OS
    object representing the broken OS with a meaningful error message.

    """
    if not isinstance(err, errors.InvalidOS):
      raise errors.ProgrammerError("Trying to initialize an OS from an"
                                   " invalid object of type %s" % type(err))

    return cls(name=err.args[0], path=err.args[1], status=err.args[2])

  def __nonzero__(self):
    return self.status == constants.OS_VALID_STATUS

  __bool__ = __nonzero__


class Node(TaggableObject):
  """Config object representing a node."""
  __slots__ = TaggableObject.__slots__ + [
    "name",
    "primary_ip",
    "secondary_ip",
    "serial_no",
    "master_candidate",
    "offline",
    "drained",
    ]


class Cluster(TaggableObject):
  """Config object representing the cluster."""
  __slots__ = TaggableObject.__slots__ + [
    "serial_no",
    "rsahostkeypub",
    "highest_used_port",
    "tcpudp_port_pool",
    "mac_prefix",
    "volume_group_name",
    "default_bridge",
    "default_hypervisor",
    "master_node",
    "master_ip",
    "master_netdev",
    "cluster_name",
    "file_storage_dir",
    "enabled_hypervisors",
    "hvparams",
    "beparams",
    "nicparams",
    "candidate_pool_size",
    "modify_etc_hosts",
    ]

  def UpgradeConfig(self):
    """Fill defaults for missing configuration values.

    """
    if self.hvparams is None:
      self.hvparams = constants.HVC_DEFAULTS
    else:
      for hypervisor in self.hvparams:
        self.hvparams[hypervisor] = FillDict(
            constants.HVC_DEFAULTS[hypervisor], self.hvparams[hypervisor])

    self.beparams = UpgradeGroupedParams(self.beparams,
                                         constants.BEC_DEFAULTS)
    migrate_default_bridge = not self.nicparams
    self.nicparams = UpgradeGroupedParams(self.nicparams,
                                          constants.NICC_DEFAULTS)
    if migrate_default_bridge:
      self.nicparams[constants.PP_DEFAULT][constants.NIC_LINK] = \
        self.default_bridge

    if self.modify_etc_hosts is None:
      self.modify_etc_hosts = True

    # default_bridge is no longer used it 2.1. The slot is left there to
    # support auto-upgrading, but will be removed in 2.2
    if self.default_bridge is not None:
      self.default_bridge = None

  def ToDict(self):
    """Custom function for cluster.

    """
    mydict = super(Cluster, self).ToDict()
    mydict["tcpudp_port_pool"] = list(self.tcpudp_port_pool)
    return mydict

  @classmethod
  def FromDict(cls, val):
    """Custom function for cluster.

    """
    obj = super(Cluster, cls).FromDict(val)
    if not isinstance(obj.tcpudp_port_pool, set):
      obj.tcpudp_port_pool = set(obj.tcpudp_port_pool)
    return obj

  def FillHV(self, instance):
    """Fill an instance's hvparams dict.

    @type instance: object
    @param instance: the instance parameter to fill
    @rtype: dict
    @return: a copy of the instance's hvparams with missing keys filled from
        the cluster defaults

    """
    return FillDict(self.hvparams.get(instance.hypervisor, {}),
                         instance.hvparams)

  def FillBE(self, instance):
    """Fill an instance's beparams dict.

    @type instance: object
    @param instance: the instance parameter to fill
    @rtype: dict
    @return: a copy of the instance's beparams with missing keys filled from
        the cluster defaults

    """
    return FillDict(self.beparams.get(constants.PP_DEFAULT, {}),
                          instance.beparams)


class SerializableConfigParser(ConfigParser.SafeConfigParser):
  """Simple wrapper over ConfigParse that allows serialization.

  This class is basically ConfigParser.SafeConfigParser with two
  additional methods that allow it to serialize/unserialize to/from a
  buffer.

  """
  def Dumps(self):
    """Dump this instance and return the string representation."""
    buf = StringIO()
    self.write(buf)
    return buf.getvalue()

  @staticmethod
  def Loads(data):
    """Load data from a string."""
    buf = StringIO(data)
    cfp = SerializableConfigParser()
    cfp.readfp(buf)
    return cfp