Synnefo » snf-ganeti

#

#

# Copyright (C) 2012 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.

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# 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.

"""Module containing utilities for virtual clusters.

Most functions manipulate file system paths and are no-ops when the environment

variables C{GANETI_ROOTDIR} and C{GANETI_HOSTNAME} are not set. See the

functions' docstrings for details.

"""

import os

from ganeti import compat

ETC_HOSTS = "/etc/hosts"

_VIRT_PATH_PREFIX = "/###-VIRTUAL-PATH-###,"

_ROOTDIR_ENVNAME = "GANETI_ROOTDIR"

_HOSTNAME_ENVNAME = "GANETI_HOSTNAME"

#: List of paths which shouldn't be virtualized

_VPATH_WHITELIST = compat.UniqueFrozenset([

  ETC_HOSTS,

  ])

def _GetRootDirectory(envname):

  """Retrieves root directory from an environment variable.

  @type envname: string

  @param envname: Environment variable name

  @rtype: string

  @return: Root directory (can be empty)

  """

  path = os.getenv(envname)

  if path:

    if not os.path.isabs(path):

      raise RuntimeError("Root directory in '%s' must be absolute: %s" %

                         (envname, path))

    return os.path.normpath(path)

  return ""

def _GetHostname(envname):

  """Retrieves virtual hostname from an environment variable.

  @type envname: string

  @param envname: Environment variable name

  @rtype: string

  @return: Host name (can be empty)

  """

  return os.getenv(envname, default="")

def _CheckHostname(hostname):

  """Very basic check for hostnames.

  @type hostname: string

  @param hostname: Hostname

  """

  if os.path.basename(hostname) != hostname:

    raise RuntimeError("Hostname '%s' can not be used for a file system"

                       " path" % hostname)

def _PreparePaths(rootdir, hostname):

  """Checks if the root directory and hostname are acceptable.

  The (node-specific) root directory must have the hostname as its last

  component. The parent directory then becomes the cluster-wide root directory.

  This is necessary as some components must be able to predict the root path on

  a remote node (e.g. copying files via scp).

  @type rootdir: string

  @param rootdir: Root directory (from environment)

  @type hostname: string

  @param hostname: Hostname (from environment)

  @rtype: tuple; (string, string, string or None)

  @return: Tuple containing cluster-global root directory, node root directory

    and virtual hostname

  """

  if bool(rootdir) ^ bool(hostname):

    raise RuntimeError("Both root directory and hostname must be specified"

                       " using the environment variables %s and %s" %

                       (_ROOTDIR_ENVNAME, _HOSTNAME_ENVNAME))

  if rootdir:

    assert rootdir == os.path.normpath(rootdir)

    _CheckHostname(hostname)

    if os.path.basename(rootdir) != hostname:

      raise RuntimeError("Last component of root directory ('%s') must match"

                         " hostname ('%s')" % (rootdir, hostname))

    return (os.path.dirname(rootdir), rootdir, hostname)

  else:

    return ("", "", None)

(_VIRT_BASEDIR, _VIRT_NODEROOT, _VIRT_HOSTNAME) = \

  _PreparePaths(_GetRootDirectory(_ROOTDIR_ENVNAME),

                _GetHostname(_HOSTNAME_ENVNAME))

assert (compat.all([_VIRT_BASEDIR, _VIRT_NODEROOT, _VIRT_HOSTNAME]) or

        not compat.any([_VIRT_BASEDIR, _VIRT_NODEROOT, _VIRT_HOSTNAME]))

def GetVirtualHostname():

  """Returns the virtual hostname.

  @rtype: string or L{None}

  """

  return _VIRT_HOSTNAME

def MakeNodeRoot(base, node_name):

  """Appends a node name to the base directory.

  """

  _CheckHostname(node_name)

  return os.path.normpath("%s/%s" % (base, node_name))

def ExchangeNodeRoot(node_name, filename,

                     _basedir=_VIRT_BASEDIR, _noderoot=_VIRT_NODEROOT):

  """Replaces the node-specific root directory in a path.

  Replaces it with the root directory for another node. Assuming

  C{/tmp/vcluster/node1} is the root directory for C{node1}, the result will be

  C{/tmp/vcluster/node3} for C{node3} (as long as a root directory is specified

  in the environment).

  """

  if _basedir:

    pure = _RemoveNodePrefix(filename, _noderoot=_noderoot)

    result = "%s/%s" % (MakeNodeRoot(_basedir, node_name), pure)

  else:

    result = filename

  return os.path.normpath(result)

def EnvironmentForHost(hostname, _basedir=_VIRT_BASEDIR):

  """Returns the environment variables for a host.

  """

  if _basedir:

    return {

      _ROOTDIR_ENVNAME: MakeNodeRoot(_basedir, hostname),

      _HOSTNAME_ENVNAME: hostname,

      }

  else:

    return {}

def AddNodePrefix(path, _noderoot=_VIRT_NODEROOT):

  """Adds a node-specific prefix to a path in a virtual cluster.

  Returned path includes user-specified root directory if specified in

  environment. As an example, the path C{/var/lib/ganeti} becomes

  C{/tmp/vcluster/node1/var/lib/ganeti} if C{/tmp/vcluster/node1} is the root

  directory specified in the environment.

  """

  assert os.path.isabs(path)

  if _noderoot:

    result = "%s/%s" % (_noderoot, path)

  else:

    result = path

  assert os.path.isabs(result)

  return os.path.normpath(result)

def _RemoveNodePrefix(path, _noderoot=_VIRT_NODEROOT):

  """Removes the node-specific prefix from a path.

  This is the opposite of L{AddNodePrefix} and removes a node-local prefix

  path.

  """

  assert os.path.isabs(path)

  norm_path = os.path.normpath(path)

  if _noderoot:

    # Make sure path is actually below node root

    norm_root = os.path.normpath(_noderoot)

    root_with_sep = "%s%s" % (norm_root, os.sep)

    prefix = os.path.commonprefix([root_with_sep, norm_path])

    if prefix == root_with_sep:

      result = norm_path[len(norm_root):]

    else:

      raise RuntimeError("Path '%s' is not below node root '%s'" %

                         (path, _noderoot))

  else:

    result = norm_path

  assert os.path.isabs(result)

  return result

def MakeVirtualPath(path, _noderoot=_VIRT_NODEROOT):

  """Virtualizes a path.

  A path is "virtualized" by stripping it of its node-specific directory and

  prepending a prefix (L{_VIRT_PATH_PREFIX}). Use L{LocalizeVirtualPath} to

  undo the process. Virtual paths are meant to be transported via RPC.

  """

  assert os.path.isabs(path)

  if _noderoot and path not in _VPATH_WHITELIST:

    return _VIRT_PATH_PREFIX + _RemoveNodePrefix(path, _noderoot=_noderoot)

  else:

    return path

def LocalizeVirtualPath(path, _noderoot=_VIRT_NODEROOT):

  """Localizes a virtual path.

  A "virtualized" path consists of a prefix (L{LocalizeVirtualPath}) and a

  local path. This function adds the node-specific directory to the local path.

  Virtual paths are meant to be transported via RPC.

  """

  assert os.path.isabs(path)

  if _noderoot and path not in _VPATH_WHITELIST:

    if path.startswith(_VIRT_PATH_PREFIX):

      return AddNodePrefix(path[len(_VIRT_PATH_PREFIX):], _noderoot=_noderoot)

    else:

      raise RuntimeError("Path '%s' is not a virtual path" % path)

  else:

    return path