Add new cfg module

As discussed on the mailing list and described here:

  http://wiki.openstack.org/CommonConfigModule

The module implements an API for defining configuration options and
reading values for those options that a user may have set in a config
file or on the command line.

The module will be part of openstack-common and glance will consume
it from there once openstack-common makes a release with an API
compatibility commitment.

Change-Id: Ib604c3de75d9066cd913c2de3007024b1f5ec9f8

3 files changed, 1935 insertions, 0 deletions

diff --git a/nova/common/__init__.py b/nova/common/__init__.py
new file mode 100644
index 000000000..0a3b98867
--- /dev/null
+++ b/nova/common/__init__.py
@@ -0,0 +1,15 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2011 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
diff --git a/nova/common/cfg.py b/nova/common/cfg.py
new file mode 100644
index 000000000..d0e7cc82c
--- /dev/null
+++ b/nova/common/cfg.py
@@ -0,0 +1,1126 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2011 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+r"""
+Configuration options which may be set on the command line or in config files.
+
+The schema for each option is defined using the Opt sub-classes e.g.
+
+    common_opts = [
+        cfg.StrOpt('bind_host',
+                   default='0.0.0.0',
+                   help='IP address to listen on'),
+        cfg.IntOpt('bind_port',
+                   default=9292,
+                   help='Port number to listen on')
+    ]
+
+Options can be strings, integers, floats, booleans, lists or 'multi strings':
+
+    enabled_apis_opt = \
+        cfg.ListOpt('enabled_apis',
+                    default=['ec2', 'osapi'],
+                    help='List of APIs to enable by default')
+
+    DEFAULT_EXTENSIONS = [
+        'nova.api.openstack.contrib.standard_extensions'
+    ]
+    osapi_extension_opt = \
+        cfg.MultiStrOpt('osapi_extension',
+                        default=DEFAULT_EXTENSIONS)
+
+Option schemas are registered with with the config manager at runtime, but
+before the option is referenced:
+
+    class ExtensionManager(object):
+
+        enabled_apis_opt = cfg.ListOpt(...)
+
+        def __init__(self, conf):
+            self.conf = conf
+            self.conf.register_opt(enabled_apis_opt)
+            ...
+
+        def _load_extensions(self):
+            for ext_factory in self.conf.osapi_extension:
+                ....
+
+A common usage pattern is for each option schema to be defined in the module or
+class which uses the option:
+
+    opts = ...
+
+    def add_common_opts(conf):
+        conf.register_opts(opts)
+
+    def get_bind_host(conf):
+        return conf.bind_host
+
+    def get_bind_port(conf):
+        return conf.bind_port
+
+An option may optionally be made available via the command line. Such options
+must registered with the config manager before the command line is parsed (for
+the purposes of --help and CLI arg validation):
+
+    cli_opts = [
+        cfg.BoolOpt('verbose',
+                    short='v',
+                    default=False,
+                    help='Print more verbose output'),
+        cfg.BoolOpt('debug',
+                    short='d',
+                    default=False,
+                    help='Print debugging output'),
+    ]
+
+    def add_common_opts(conf):
+        conf.register_cli_opts(cli_opts)
+
+The config manager has a single CLI option defined by default, --config-file:
+
+    class ConfigOpts(object):
+
+        config_file_opt = \
+            MultiStrOpt('config-file',
+                        ...
+
+        def __init__(self, ...):
+            ...
+            self.register_cli_opt(self.config_file_opt)
+
+Option values are parsed from any supplied config files using SafeConfigParser.
+If none are specified, a default set is used e.g. glance-api.conf and
+glance-common.conf:
+
+    glance-api.conf:
+      [DEFAULT]
+      bind_port = 9292
+
+    glance-common.conf:
+      [DEFAULT]
+      bind_host = 0.0.0.0
+
+Option values in config files override those on the command line. Config files
+are parsed in order, with values in later files overriding those in earlier
+files.
+
+The parsing of CLI args and config files is initiated by invoking the config
+manager e.g.
+
+    conf = ConfigOpts()
+    conf.register_opt(BoolOpt('verbose', ...))
+    conf(sys.argv[1:])
+    if conf.verbose:
+        ...
+
+Options can be registered as belonging to a group:
+
+    rabbit_group = cfg.OptionGroup(name='rabbit',
+                                   title='RabbitMQ options')
+
+    rabbit_host_opt = \
+        cfg.StrOpt('host',
+                   group='rabbit',
+                   default='localhost',
+                   help='IP/hostname to listen on'),
+    rabbit_port_opt = \
+        cfg.IntOpt('port',
+                   default=5672,
+                   help='Port number to listen on')
+    rabbit_ssl_opt = \
+        conf.BoolOpt('use_ssl',
+                     default=False,
+                     help='Whether to support SSL connections')
+
+    def register_rabbit_opts(conf):
+        conf.register_group(rabbit_group)
+        # options can be registered under a group in any of these ways:
+        conf.register_opt(rabbit_host_opt)
+        conf.register_opt(rabbit_port_opt, group='rabbit')
+        conf.register_opt(rabbit_ssl_opt, group=rabbit_group)
+
+If no group is specified, options belong to the 'DEFAULT' section of config
+files:
+
+    glance-api.conf:
+      [DEFAULT]
+      bind_port = 9292
+      ...
+
+      [rabbit]
+      host = localhost
+      port = 5672
+      use_ssl = False
+      userid = guest
+      password = guest
+      virtual_host = /
+
+Command-line options in a group are automatically prefixed with the group name:
+
+    --rabbit-host localhost --rabbit-use-ssl False
+
+Option values in the default group are referenced as attributes/properties on
+the config manager; groups are also attributes on the config manager, with
+attributes for each of the options associated with the group:
+
+    server.start(app, conf.bind_port, conf.bind_host, conf)
+
+    self.connection = kombu.connection.BrokerConnection(
+        hostname=conf.rabbit.host,
+        port=conf.rabbit.port,
+        ...)
+
+Option values may reference other values using PEP 292 string substitution:
+
+    opts = [
+        cfg.StrOpt('state_path',
+                   default=os.path.join(os.path.dirname(__file__), '../'),
+                   help='Top-level directory for maintaining nova state'),
+        cfg.StrOpt('sqlite_db',
+                   default='nova.sqlite',
+                   help='file name for sqlite'),
+        cfg.StrOpt('sql_connection',
+                   default='sqlite:///$state_path/$sqlite_db',
+                   help='connection string for sql database'),
+    ]
+
+Note that interpolation can be avoided by using '$$'.
+"""
+
+import sys
+import ConfigParser
+import copy
+import optparse
+import os
+import string
+
+
+class Error(Exception):
+    """Base class for cfg exceptions."""
+
+    def __init__(self, msg=None):
+        self.msg = msg
+
+    def __str__(self):
+        return self.msg
+
+
+class ArgsAlreadyParsedError(Error):
+    """Raised if a CLI opt is registered after parsing."""
+
+    def __str__(self):
+        ret = "arguments already parsed"
+        if self.msg:
+            ret += ": " + self.msg
+        return ret
+
+
+class NoSuchOptError(Error):
+    """Raised if an opt which doesn't exist is referenced."""
+
+    def __init__(self, opt_name, group=None):
+        self.opt_name = opt_name
+        self.group = group
+
+    def __str__(self):
+        if self.group is None:
+            return "no such option: %s" % self.opt_name
+        else:
+            return "no such option in group %s: %s" % (self.group.name,
+                                                       self.opt_name)
+
+
+class NoSuchGroupError(Error):
+    """Raised if a group which doesn't exist is referenced."""
+
+    def __init__(self, group_name):
+        self.group_name = group_name
+
+    def __str__(self):
+        return "no such group: %s" % self.group_name
+
+
+class DuplicateOptError(Error):
+    """Raised if multiple opts with the same name are registered."""
+
+    def __init__(self, opt_name):
+        self.opt_name = opt_name
+
+    def __str__(self):
+        return "duplicate option: %s" % self.opt_name
+
+
+class TemplateSubstitutionError(Error):
+    """Raised if an error occurs substituting a variable in an opt value."""
+
+    def __str__(self):
+        return "template substitution error: %s" % self.msg
+
+
+class ConfigFilesNotFoundError(Error):
+    """Raised if one or more config files are not found."""
+
+    def __init__(self, config_files):
+        self.config_files = config_files
+
+    def __str__(self):
+        return 'Failed to read some config files: %s' % \
+            string.join(self.config_files, ',')
+
+
+class ConfigFileParseError(Error):
+    """Raised if there is an error parsing a config file."""
+
+    def __init__(self, config_file, msg):
+        self.config_file = config_file
+        self.msg = msg
+
+    def __str__(self):
+        return 'Failed to parse %s: %s' % (self.config_file, self.msg)
+
+
+class ConfigFileValueError(Error):
+    """Raised if a config file value does not match its opt type."""
+    pass
+
+
+def find_config_files(project=None, prog=None):
+    """Return a list of default configuration files.
+
+    We default to two config files: [${project}.conf, ${prog}.conf]
+
+    And we look for those config files in the following directories:
+
+      ~/.${project}/
+      ~/
+      /etc/${project}/
+      /etc/
+
+    We return an absolute path for (at most) one of each the default config
+    files, for the topmost directory it exists in.
+
+    For example, if project=foo, prog=bar and /etc/foo/foo.conf, /etc/bar.conf
+    and ~/.foo/bar.conf all exist, then we return ['/etc/foo/foo.conf',
+    '~/.foo/bar.conf']
+
+    If no project name is supplied, we only look for ${prog.conf}.
+
+    :param project: an optional project name
+    :param prog: the program name, defaulting to the basename of sys.argv[0]
+    """
+    if prog is None:
+        prog = os.path.basename(sys.argv[0])
+
+    fix_path = lambda p: os.path.abspath(os.path.expanduser(p))
+
+    cfg_dirs = [
+        fix_path(os.path.join('~', '.' + project)) if project else None,
+        fix_path('~'),
+        os.path.join('/etc', project) if project else None,
+        '/etc'
+        ]
+    cfg_dirs = filter(bool, cfg_dirs)
+
+    def search_dirs(dirs, basename):
+        for d in dirs:
+            path = os.path.join(d, basename)
+            if os.path.exists(path):
+                return path
+
+    config_files = []
+    if project:
+        config_files.append(search_dirs(cfg_dirs, '%s.conf' % project))
+    config_files.append(search_dirs(cfg_dirs, '%s.conf' % prog))
+
+    return filter(bool, config_files)
+
+
+def _is_opt_registered(opts, opt):
+    """Check whether an opt with the same name is already registered.
+
+    The same opt may be registered multiple times, with only the first
+    registration having any effect. However, it is an error to attempt
+    to register a different opt with the same name.
+
+    :param opts: the set of opts already registered
+    :param opt: the opt to be registered
+    :returns: True if the opt was previously registered, False otherwise
+    :raises: DuplicateOptError if a naming conflict is detected
+    """
+    if opt.dest in opts:
+        if opts[opt.dest]['opt'] is not opt:
+            raise DuplicateOptError(opt.name)
+        return True
+    else:
+        return False
+
+
+class Opt(object):
+
+    """Base class for all configuration options.
+
+    An Opt object has no public methods, but has a number of public string
+    properties:
+
+      name:
+        the name of the option, which may include hyphens
+      dest:
+        the (hyphen-less) ConfigOpts property which contains the option value
+      short:
+        a single character CLI option name
+      default:
+        the default value of the option
+      metavar:
+        the name shown as the argument to a CLI option in --help output
+      help:
+        an string explaining how the options value is used
+    """
+
+    def __init__(self, name, dest=None, short=None,
+                 default=None, metavar=None, help=None):
+        """Construct an Opt object.
+
+        The only required parameter is the option's name. However, it is
+        common to also supply a default and help string for all options.
+
+        :param name: the option's name
+        :param dest: the name of the corresponding ConfigOpts property
+        :param short: a single character CLI option name
+        :param default: the default value of the option
+        :param metavar: the option argument to show in --help
+        :param help: an explanation of how the option is used
+        """
+        self.name = name
+        if dest is None:
+            self.dest = self.name.replace('-', '_')
+        else:
+            self.dest = dest
+        self.short = short
+        self.default = default
+        self.metavar = metavar
+        self.help = help
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieves the option value from a ConfigParser object.
+
+        This is the method ConfigOpts uses to look up the option value from
+        config files. Most opt types override this method in order to perform
+        type appropriate conversion of the returned value.
+
+        :param cparser: a ConfigParser object
+        :param section: a section name
+        """
+        return cparser.get(section, self.dest)
+
+    def _add_to_cli(self, parser, group=None):
+        """Makes the option available in the command line interface.
+
+        This is the method ConfigOpts uses to add the opt to the CLI interface
+        as appropriate for the opt type. Some opt types may extend this method,
+        others may just extend the helper methods it uses.
+
+        :param parser: the CLI option parser
+        :param group: an optional OptGroup object
+        """
+        container = self._get_optparse_container(parser, group)
+        kwargs = self._get_optparse_kwargs(group)
+        prefix = self._get_optparse_prefix('', group)
+        self._add_to_optparse(container, self.name, self.short, kwargs, prefix)
+
+    def _add_to_optparse(self, container, name, short, kwargs, prefix=''):
+        """Add an option to an optparse parser or group.
+
+        :param container: an optparse.OptionContainer object
+        :param name: the opt name
+        :param short: the short opt name
+        :param kwargs: the keyword arguments for add_option()
+        :param prefix: an optional prefix to prepend to the opt name
+        :raises: DuplicateOptError if a naming confict is detected
+        """
+        args = ['--' + prefix + name]
+        if short:
+            args += ['-' + short]
+        for a in args:
+            if container.has_option(a):
+                raise DuplicateOptError(a)
+        container.add_option(*args, **kwargs)
+
+    def _get_optparse_container(self, parser, group):
+        """Returns an optparse.OptionContainer.
+
+        :param parser: an optparse.OptionParser
+        :param group: an (optional) OptGroup object
+        :returns: an optparse.OptionGroup if a group is given, else the parser
+        """
+        if group is not None:
+            return group._get_optparse_group(parser)
+        else:
+            return parser
+
+    def _get_optparse_kwargs(self, group, **kwargs):
+        """Build a dict of keyword arguments for optparse's add_option().
+
+        Most opt types extend this method to customize the behaviour of the
+        options added to optparse.
+
+        :param group: an optional group
+        :param kwargs: optional keyword arguments to add to
+        :returns: a dict of keyword arguments
+        """
+        dest = self.dest
+        if group is not None:
+            dest = group.name + '_' + dest
+        kwargs.update({
+                'dest': dest,
+                'metavar': self.metavar,
+                'help': self.help,
+                })
+        return kwargs
+
+    def _get_optparse_prefix(self, prefix, group):
+        """Build a prefix for the CLI option name, if required.
+
+        CLI options in a group are prefixed with the group's name in order
+        to avoid conflicts between similarly named options in different
+        groups.
+
+        :param prefix: an existing prefix to append to (e.g. 'no' or '')
+        :param group: an optional OptGroup object
+        :returns: a CLI option prefix including the group name, if appropriate
+        """
+        if group is not None:
+            return group.name + '-' + prefix
+        else:
+            return prefix
+
+
+class StrOpt(Opt):
+    """
+    String opts do not have their values transformed and are returned as
+    str objects.
+    """
+    pass
+
+
+class BoolOpt(Opt):
+
+    """
+    Bool opts are set to True or False on the command line using --optname or
+    --noopttname respectively.
+
+    In config files, boolean values are case insensitive and can be set using
+    1/0, yes/no, true/false or on/off.
+    """
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieve the opt value as a boolean from ConfigParser."""
+        return cparser.getboolean(section, self.dest)
+
+    def _add_to_cli(self, parser, group=None):
+        """Extends the base class method to add the --nooptname option."""
+        super(BoolOpt, self)._add_to_cli(parser, group)
+        self._add_inverse_to_optparse(parser, group)
+
+    def _add_inverse_to_optparse(self, parser, group):
+        """Add the --nooptname option to the option parser."""
+        container = self._get_optparse_container(parser, group)
+        kwargs = self._get_optparse_kwargs(group, action='store_false')
+        prefix = self._get_optparse_prefix('no', group)
+        self._add_to_optparse(container, self.name, None, kwargs, prefix)
+
+    def _get_optparse_kwargs(self, group, action='store_true', **kwargs):
+        """Extends the base optparse keyword dict for boolean options."""
+        return super(BoolOpt,
+                     self)._get_optparse_kwargs(group, action=action, **kwargs)
+
+
+class IntOpt(Opt):
+
+    """Int opt values are converted to integers using the int() builtin."""
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieve the opt value as a integer from ConfigParser."""
+        return cparser.getint(section, self.dest)
+
+    def _get_optparse_kwargs(self, group, **kwargs):
+        """Extends the base optparse keyword dict for integer options."""
+        return super(IntOpt,
+                     self)._get_optparse_kwargs(group, type='int', **kwargs)
+
+
+class FloatOpt(Opt):
+
+    """Float opt values are converted to floats using the float() builtin."""
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieve the opt value as a float from ConfigParser."""
+        return cparser.getfloat(section, self.dest)
+
+    def _get_optparse_kwargs(self, group, **kwargs):
+        """Extends the base optparse keyword dict for float options."""
+        return super(FloatOpt,
+                     self)._get_optparse_kwargs(group, type='float', **kwargs)
+
+
+class ListOpt(Opt):
+
+    """
+    List opt values are simple string values separated by commas. The opt value
+    is a list containing these strings.
+    """
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieve the opt value as a list from ConfigParser."""
+        return cparser.get(section, self.dest).split(',')
+
+    def _get_optparse_kwargs(self, group, **kwargs):
+        """Extends the base optparse keyword dict for list options."""
+        return super(ListOpt,
+                     self)._get_optparse_kwargs(group,
+                                                type='string',
+                                                action='callback',
+                                                callback=self._parse_list,
+                                                **kwargs)
+
+    def _parse_list(self, option, opt, value, parser):
+        """An optparse callback for parsing an option value into a list."""
+        setattr(parser.values, self.dest, value.split(','))
+
+
+class MultiStrOpt(Opt):
+
+    """
+    Multistr opt values are string opts which may be specified multiple times.
+    The opt value is a list containing all the string values specified.
+    """
+
+    def _get_from_config_parser(self, cparser, section):
+        """Retrieve the opt value as a multistr from ConfigParser."""
+        # FIXME(markmc): values spread across the CLI and multiple
+        #                config files should be appended
+        value = \
+            super(MultiStrOpt, self)._get_from_config_parser(cparser, section)
+        return value if value is None else [value]
+
+    def _get_optparse_kwargs(self, group, **kwargs):
+        """Extends the base optparse keyword dict for multi str options."""
+        return super(MultiStrOpt,
+                     self)._get_optparse_kwargs(group, action='append')
+
+
+class OptGroup(object):
+
+    """
+    Represents a group of opts.
+
+    CLI opts in the group are automatically prefixed with the group name.
+
+    Each group corresponds to a section in config files.
+
+    An OptGroup object has no public methods, but has a number of public string
+    properties:
+
+      name:
+        the name of the group
+      title:
+        the group title as displayed in --help
+      help:
+        the group description as displayed in --help
+    """
+
+    def __init__(self, name, title=None, help=None):
+        """Constructs an OptGroup object.
+
+        :param name: the group name
+        :param title: the group title for --help
+        :param help: the group description for --help
+        """
+        self.name = name
+        if title is None:
+            self.title = "%s options" % title
+        else:
+            self.title = title
+        self.help = help
+
+        self._opts = {}  # dict of dicts of {opt:, override:, default:)
+        self._optparse_group = None
+
+    def _register_opt(self, opt):
+        """Add an opt to this group.
+
+        :param opt: an Opt object
+        :returns: False if previously registered, True otherwise
+        :raises: DuplicateOptError if a naming conflict is detected
+        """
+        if _is_opt_registered(self._opts, opt):
+            return False
+
+        self._opts[opt.dest] = {'opt': opt, 'override': None, 'default': None}
+
+        return True
+
+    def _get_optparse_group(self, parser):
+        """Build an optparse.OptionGroup for this group."""
+        if self._optparse_group is None:
+            self._optparse_group = \
+                optparse.OptionGroup(parser, self.title, self.help)
+        return self._optparse_group
+
+
+class ConfigOpts(object):
+
+    """
+    Config options which may be set on the command line or in config files.
+
+    ConfigOpts is a configuration option manager with APIs for registering
+    option schemas, grouping options, parsing option values and retrieving
+    the values of options.
+    """
+
+    def __init__(self,
+                 project=None,
+                 prog=None,
+                 version=None,
+                 usage=None,
+                 default_config_files=None):
+        """Construct a ConfigOpts object.
+
+        Automatically registers the --config-file option with either a supplied
+        list of default config files, or a list from find_config_files().
+
+        :param project: the toplevel project name, used to locate config files
+        :param prog: the name of the program (defaults to sys.argv[0] basename)
+        :param version: the program version (for --version)
+        :param usage: a usage string (%prog will be expanded)
+        :param default_config_files: config files to use by default
+        """
+        if prog is None:
+            prog = os.path.basename(sys.argv[0])
+
+        if default_config_files is None:
+            default_config_files = find_config_files(project, prog)
+
+        self.project = project
+        self.prog = prog
+        self.version = version
+        self.usage = usage
+        self.default_config_files = default_config_files
+
+        self._opts = {}  # dict of dicts of (opt:, override:, default:)
+        self._groups = {}
+
+        self._args = None
+        self._cli_values = {}
+
+        self._oparser = optparse.OptionParser(prog=self.prog,
+                                              version=self.version,
+                                              usage=self.usage)
+        self._cparser = None
+
+        self.register_cli_opt(\
+            MultiStrOpt('config-file',
+                        default=self.default_config_files,
+                        metavar='PATH',
+                        help='Path to a config file to use. Multiple config '
+                             'files can be specified, with values in later '
+                             'files taking precedence. The default files used '
+                             'are: %s' % (self.default_config_files, )))
+
+    def __call__(self, args=None):
+        """Parse command line arguments and config files.
+
+        Calling a ConfigOpts object causes the supplied command line arguments
+        and config files to be parsed, causing opt values to be made available
+        as attributes of the object.
+
+        The object may be called multiple times, each time causing the previous
+        set of values to be overwritten.
+
+        :params args: command line arguments (defaults to sys.argv[1:])
+        :returns: the list of arguments left over after parsing options
+        :raises: SystemExit, ConfigFilesNotFoundError, ConfigFileParseError
+        """
+        self.reset()
+
+        self._args = args
+
+        (values, args) = self._oparser.parse_args(self._args)
+
+        self._cli_values = vars(values)
+
+        if self.config_file:
+            self._parse_config_files(self.config_file)
+
+        return args
+
+    def __getattr__(self, name):
+        """Look up an option value and perform string substitution.
+
+        :param name: the opt name (or 'dest', more precisely)
+        :returns: the option value (after string subsititution) or a GroupAttr
+        :raises: NoSuchOptError,ConfigFileValueError,TemplateSubstitutionError
+        """
+        return self._substitute(self._get(name))
+
+    def reset(self):
+        """Reset the state of the object to before it was called."""
+        self._args = None
+        self._cli_values = None
+        self._cparser = None
+
+    def register_opt(self, opt, group=None):
+        """Register an option schema.
+
+        Registering an option schema makes any option value which is previously
+        or subsequently parsed from the command line or config files available
+        as an attribute of this object.
+
+        :param opt: an instance of an Opt sub-class
+        :param group: an optional OptGroup object or group name
+        :return: False if the opt was already register, True otherwise
+        :raises: DuplicateOptError
+        """
+        if group is not None:
+            return self._get_group(group)._register_opt(opt)
+
+        if _is_opt_registered(self._opts, opt):
+            return False
+
+        self._opts[opt.dest] = {'opt': opt, 'override': None, 'default': None}
+
+        return True
+
+    def register_opts(self, opts, group=None):
+        """Register multiple option schemas at once."""
+        for opt in opts:
+            self.register_opt(opt, group)
+
+    def register_cli_opt(self, opt, group=None):
+        """Register a CLI option schema.
+
+        CLI option schemas must be registered before the command line and
+        config files are parsed. This is to ensure that all CLI options are
+        show in --help and option validation works as expected.
+
+        :param opt: an instance of an Opt sub-class
+        :param group: an optional OptGroup object or group name
+        :return: False if the opt was already register, True otherwise
+        :raises: DuplicateOptError, ArgsAlreadyParsedError
+        """
+        if self._args != None:
+            raise ArgsAlreadyParsedError("cannot register CLI option")
+
+        if not self.register_opt(opt, group):
+            return False
+
+        if group is not None:
+            group = self._get_group(group)
+
+        opt._add_to_cli(self._oparser, group)
+
+        return True
+
+    def register_cli_opts(self, opts, group=None):
+        """Register multiple CLI option schemas at once."""
+        for opt in opts:
+            self.register_cli_opt(opt, group)
+
+    def register_group(self, group):
+        """Register an option group.
+
+        An option group must be registered before options can be registered
+        with the group.
+
+        :param group: an OptGroup object
+        """
+        if group.name in self._groups:
+            return
+
+        self._groups[group.name] = copy.copy(group)
+
+    def set_override(self, name, override, group=None):
+        """Override an opt value.
+
+        Override the command line, config file and default values of a
+        given option.
+
+        :param name: the name/dest of the opt
+        :param override: the override value
+        :param group: an option OptGroup object or group name
+        :raises: NoSuchOptError, NoSuchGroupError
+        """
+        opt_info = self._get_opt_info(name, group)
+        opt_info['override'] = override
+
+    def set_default(self, name, default, group=None):
+        """Override an opt's default value.
+
+        Override the default value of given option. A command line or
+        config file value will still take precedence over this default.
+
+        :param name: the name/dest of the opt
+        :param default: the default value
+        :param group: an option OptGroup object or group name
+        :raises: NoSuchOptError, NoSuchGroupError
+        """
+        opt_info = self._get_opt_info(name, group)
+        opt_info['default'] = default
+
+    def log_opt_values(self, logger, lvl):
+        """Log the value of all registered opts.
+
+        It's often useful for an app to log its configuration to a log file at
+        startup for debugging. This method dumps to the entire config state to
+        the supplied logger at a given log level.
+
+        :param logger: a logging.Logger object
+        :param lvl: the log level (e.g. logging.DEBUG) arg to logger.log()
+        """
+        logger.log(lvl, "*" * 80)
+        logger.log(lvl, "Configuration options gathered from:")
+        logger.log(lvl, "command line args: %s", self._args)
+        logger.log(lvl, "config files: %s", self.config_file)
+        logger.log(lvl, "=" * 80)
+
+        for opt_name in sorted(self._opts):
+            logger.log(lvl, "%-30s = %s", opt_name, getattr(self, opt_name))
+
+        for group_name in self._groups:
+            group_attr = self.GroupAttr(self, group_name)
+            for opt_name in sorted(self._groups[group_name]._opts):
+                logger.log(lvl, "%-30s = %s",
+                           "%s.%s" % (group_name, opt_name),
+                           getattr(group_attr, opt_name))
+
+        logger.log(lvl, "*" * 80)
+
+    def print_usage(self, file=None):
+        """Print the usage message for the current program."""
+        self._oparser.print_usage(file)
+
+    def _get(self, name, group=None):
+        """Look up an option value.
+
+        :param name: the opt name (or 'dest', more precisely)
+        :param group: an option OptGroup
+        :returns: the option value, or a GroupAttr object
+        :raises: NoSuchOptError, NoSuchGroupError, ConfigFileValueError,
+                 TemplateSubstitutionError
+        """
+        if group is None and name in self._groups:
+            return self.GroupAttr(self, name)
+
+        if group is not None:
+            group = self._get_group(group)
+
+        info = self._get_opt_info(name, group)
+        default, opt, override = map(lambda k: info[k], sorted(info.keys()))
+
+        if override is not None:
+            return override
+
+        if self._cparser is not None:
+            section = group.name if group is not None else 'DEFAULT'
+            try:
+                return opt._get_from_config_parser(self._cparser, section)
+            except (ConfigParser.NoOptionError,
+                    ConfigParser.NoSectionError):
+                pass
+            except ValueError, ve:
+                raise ConfigFileValueError(str(ve))
+
+        name = name if group is None else group.name + '_' + name
+        value = self._cli_values.get(name, None)
+        if value is not None:
+            return value
+
+        if default is not None:
+            return default
+
+        return opt.default
+
+    def _substitute(self, value):
+        """Perform string template substitution.
+
+        Substititue any template variables (e.g. $foo, ${bar}) in the supplied
+        string value(s) with opt values.
+
+        :param value: the string value, or list of string values
+        :returns: the substituted string(s)
+        """
+        if type(value) is list:
+            return [self._substitute(i) for i in value]
+        elif type(value) is str:
+            tmpl = string.Template(value)
+            return tmpl.safe_substitute(self.StrSubWrapper(self))
+        else:
+            return value
+
+    def _get_group(self, group_or_name):
+        """Looks up a OptGroup object.
+
+        Helper function to return an OptGroup given a parameter which can
+        either be the group's name or an OptGroup object.
+
+        The OptGroup object returned is from the internal dict of OptGroup
+        objects, which will be a copy of any OptGroup object that users of
+        the API have access to.
+
+        :param group_or_name: the group's name or the OptGroup object itself
+        :raises: NoSuchGroupError
+        """
+        if isinstance(group_or_name, OptGroup):
+            group_name = group_or_name.name
+        else:
+            group_name = group_or_name
+
+        if not group_name in self._groups:
+            raise NoSuchGroupError(group_name)
+
+        return self._groups[group_name]
+
+    def _get_opt_info(self, opt_name, group=None):
+        """Return the (opt, override, default) dict for an opt.
+
+        :param opt_name: an opt name/dest
+        :param group: an optional group name or OptGroup object
+        :raises: NoSuchOptError, NoSuchGroupError
+        """
+        if group is None:
+            opts = self._opts
+        else:
+            group = self._get_group(group)
+            opts = group._opts
+
+        if not opt_name in opts:
+            raise NoSuchOptError(opt_name, group)
+
+        return opts[opt_name]
+
+    def _parse_config_files(self, config_files):
+        """Parse the supplied configuration files.
+
+        :raises: ConfigFilesNotFoundError, ConfigFileParseError
+        """
+        self._cparser = ConfigParser.SafeConfigParser(allow_no_value=True)
+
+        try:
+            read_ok = self._cparser.read(config_files)
+        except ConfigParser.ParsingError, cpe:
+            raise ConfigFileParseError(cpe.filename, cpe.message)
+
+        if read_ok != config_files:
+            not_read_ok = filter(lambda f: f not in read_ok, config_files)
+            raise ConfigFilesNotFoundError(not_read_ok)
+
+    class GroupAttr(object):
+
+        """
+        A helper class representing the option values of a group as attributes.
+        """
+
+        def __init__(self, conf, group):
+            """Construct a GroupAttr object.
+
+            :param conf: a ConfigOpts object
+            :param group: a group name or OptGroup object
+            """
+            self.conf = conf
+            self.group = group
+
+        def __getattr__(self, name):
+            """Look up an option value and perform template substitution."""
+            return self.conf._substitute(self.conf._get(name, self.group))
+
+    class StrSubWrapper(object):
+
+        """
+        A helper class exposing opt values as a dict for string substitution.
+        """
+
+        def __init__(self, conf):
+            """Construct a StrSubWrapper object.
+
+            :param conf: a ConfigOpts object
+            """
+            self.conf = conf
+
+        def __getitem__(self, key):
+            """Look up an opt value from the ConfigOpts object.
+
+            :param key: an opt name
+            :returns: an opt value
+            :raises: TemplateSubstitutionError if attribute is a group
+            """
+            value = getattr(self.conf, key)
+            if isinstance(value, self.conf.GroupAttr):
+                raise TemplateSubstitutionError(
+                    'substituting group %s not supported' % key)
+            return value
+
+
+class CommonConfigOpts(ConfigOpts):
+
+    DEFAULT_LOG_FORMAT = "%(asctime)s %(levelname)8s [%(name)s] %(message)s"
+    DEFAULT_LOG_DATE_FORMAT = "%Y-%m-%d %H:%M:%S"
+
+    common_cli_opts = [
+        BoolOpt('debug',
+                short='d',
+                default=False,
+                help='Print debugging output'),
+        BoolOpt('verbose',
+                short='v',
+                default=False,
+                help='Print more verbose output'),
+        ]
+
+    logging_cli_opts = [
+        StrOpt('log-config',
+               metavar='PATH',
+               help='If this option is specified, the logging configuration '
+                    'file specified is used and overrides any other logging '
+                    'options specified. Please see the Python logging module '
+                    'documentation for details on logging configuration '
+                    'files.'),
+        StrOpt('log-format',
+               default=DEFAULT_LOG_FORMAT,
+               metavar='FORMAT',
+               help='A logging.Formatter log message format string which may '
+                    'use any of the available logging.LogRecord attributes. '
+                    'Default: %default'),
+        StrOpt('log-date-format',
+               default=DEFAULT_LOG_DATE_FORMAT,
+               metavar='DATE_FORMAT',
+               help='Format string for %(asctime)s in log records. '
+                    'Default: %default'),
+        StrOpt('log-file',
+               metavar='PATH',
+               help='(Optional) Name of log file to output to. '
+                    'If not set, logging will go to stdout.'),
+        StrOpt('log-dir',
+               help='(Optional) The directory to keep log files in '
+                    '(will be prepended to --logfile)'),
+        BoolOpt('use-syslog',
+                default=False,
+                help='Use syslog for logging.'),
+        ]
+
+    def __init__(self, **kwargs):
+        super(CommonConfigOpts, self).__init__(**kwargs)
+        self.register_cli_opts(self.common_cli_opts)
+        self.register_cli_opts(self.logging_cli_opts)
diff --git a/nova/tests/test_cfg.py b/nova/tests/test_cfg.py
new file mode 100644
index 000000000..90147f589
--- /dev/null
+++ b/nova/tests/test_cfg.py
@@ -0,0 +1,794 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2011 Red Hat, Inc.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import os
+import sys
+import StringIO
+import tempfile
+import unittest
+
+import stubout
+
+from nova import test
+from nova.common.cfg import *
+
+
+class BaseTestCase(test.TestCase):
+
+    def setUp(self):
+        self.conf = ConfigOpts(prog='test',
+                               version='1.0',
+                               usage='%prog FOO BAR',
+                               default_config_files=[])
+        self.tempfiles = []
+        self.stubs = stubout.StubOutForTesting()
+
+    def tearDown(self):
+        self.remove_tempfiles()
+        self.stubs.UnsetAll()
+
+    def create_tempfiles(self, files):
+        for (basename, contents) in files:
+            (fd, path) = tempfile.mkstemp(prefix=basename)
+            self.tempfiles.append(path)
+            try:
+                os.write(fd, contents)
+            finally:
+                os.close(fd)
+        return self.tempfiles[-len(files):]
+
+    def remove_tempfiles(self):
+        for p in self.tempfiles:
+            os.remove(p)
+
+
+class LeftoversTestCase(BaseTestCase):
+
+    def test_leftovers(self):
+        self.conf.register_cli_opt(StrOpt('foo'))
+        self.conf.register_cli_opt(StrOpt('bar'))
+
+        leftovers = self.conf(['those', '--foo', 'this',
+                               'thems', '--bar', 'that', 'these'])
+
+        self.assertEquals(leftovers, ['those', 'thems', 'these'])
+
+
+class FindConfigFilesTestCase(BaseTestCase):
+
+    def test_find_config_files(self):
+        config_files = \
+            [os.path.expanduser('~/.blaa/blaa.conf'), '/etc/foo.conf']
+
+        self.stubs.Set(os.path, 'exists', lambda p: p in config_files)
+
+        self.assertEquals(find_config_files(project='blaa', prog='foo'),
+                          config_files)
+
+
+class CliOptsTestCase(BaseTestCase):
+
+    def _do_cli_test(self, opt_class, default, cli_args, value):
+        self.conf.register_cli_opt(opt_class('foo', default=default))
+
+        self.conf(cli_args)
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, value)
+
+    def test_str_default(self):
+        self._do_cli_test(StrOpt, None, [], None)
+
+    def test_str_arg(self):
+        self._do_cli_test(StrOpt, None, ['--foo', 'bar'], 'bar')
+
+    def test_bool_default(self):
+        self._do_cli_test(BoolOpt, False, [], False)
+
+    def test_bool_arg(self):
+        self._do_cli_test(BoolOpt, None, ['--foo'], True)
+
+    def test_bool_arg_inverse(self):
+        self._do_cli_test(BoolOpt, None, ['--foo', '--nofoo'], False)
+
+    def test_int_default(self):
+        self._do_cli_test(IntOpt, 10, [], 10)
+
+    def test_int_arg(self):
+        self._do_cli_test(IntOpt, None, ['--foo=20'], 20)
+
+    def test_float_default(self):
+        self._do_cli_test(FloatOpt, 1.0, [], 1.0)
+
+    def test_float_arg(self):
+        self._do_cli_test(FloatOpt, None, ['--foo', '2.0'], 2.0)
+
+    def test_list_default(self):
+        self._do_cli_test(ListOpt, ['bar'], [], ['bar'])
+
+    def test_list_arg(self):
+        self._do_cli_test(ListOpt, None,
+                          ['--foo', 'blaa,bar'], ['blaa', 'bar'])
+
+    def test_multistr_default(self):
+        self._do_cli_test(MultiStrOpt, ['bar'], [], ['bar'])
+
+    def test_multistr_arg(self):
+        self._do_cli_test(MultiStrOpt, None,
+                          ['--foo', 'blaa', '--foo', 'bar'], ['blaa', 'bar'])
+
+    def test_help(self):
+        self.stubs.Set(sys, 'stdout', StringIO.StringIO())
+        self.assertRaisesRegexp(SystemExit, '0', self.conf, ['--help'])
+        self.assertIn('FOO BAR', sys.stdout.getvalue())
+        self.assertIn('--version', sys.stdout.getvalue())
+        self.assertIn('--help', sys.stdout.getvalue())
+        self.assertIn('--config-file=PATH', sys.stdout.getvalue())
+
+    def test_version(self):
+        self.stubs.Set(sys, 'stdout', StringIO.StringIO())
+        self.assertRaisesRegexp(SystemExit, '0', self.conf, ['--version'])
+        self.assertIn('1.0', sys.stdout.getvalue())
+
+    def test_config_file(self):
+        paths = self.create_tempfiles([('1.conf', '[DEFAULT]'),
+                                       ('2.conf', '[DEFAULT]')])
+
+        self.conf(['--config-file', paths[0], '--config-file', paths[1]])
+
+        self.assertEquals(self.conf.config_file, paths)
+
+
+class ConfigFileOptsTestCase(BaseTestCase):
+
+    def test_str_default(self):
+        self.conf.register_opt(StrOpt('foo', default='bar'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 'bar')
+
+    def test_str_value(self):
+        self.conf.register_opt(StrOpt('foo'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 'bar')
+
+    def test_str_value_override(self):
+        self.conf.register_cli_opt(StrOpt('foo'))
+
+        paths = self.create_tempfiles([('1.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = baar\n'),
+                                       ('2.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = baaar\n')])
+
+        self.conf(['--foo', 'bar',
+                   '--config-file', paths[0],
+                   '--config-file', paths[1]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 'baaar')
+
+    def test_int_default(self):
+        self.conf.register_opt(IntOpt('foo', default=666))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 666)
+
+    def test_int_value(self):
+        self.conf.register_opt(IntOpt('foo'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 666\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 666)
+
+    def test_int_value_override(self):
+        self.conf.register_cli_opt(IntOpt('foo'))
+
+        paths = self.create_tempfiles([('1.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 66\n'),
+                                       ('2.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 666\n')])
+
+        self.conf(['--foo', '6',
+                   '--config-file', paths[0],
+                   '--config-file', paths[1]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 666)
+
+    def test_float_default(self):
+        self.conf.register_opt(FloatOpt('foo', default=6.66))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 6.66)
+
+    def test_float_value(self):
+        self.conf.register_opt(FloatOpt('foo'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 6.66\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 6.66)
+
+    def test_float_value_override(self):
+        self.conf.register_cli_opt(FloatOpt('foo'))
+
+        paths = self.create_tempfiles([('1.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 6.6\n'),
+                                       ('2.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = 6.66\n')])
+
+        self.conf(['--foo', '6',
+                   '--config-file', paths[0],
+                   '--config-file', paths[1]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, 6.66)
+
+    def test_list_default(self):
+        self.conf.register_opt(ListOpt('foo', default=['bar']))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['bar'])
+
+    def test_list_value(self):
+        self.conf.register_opt(ListOpt('foo'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['bar'])
+
+    def test_list_value_override(self):
+        self.conf.register_cli_opt(ListOpt('foo'))
+
+        paths = self.create_tempfiles([('1.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar,bar\n'),
+                                       ('2.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = b,a,r\n')])
+
+        self.conf(['--foo', 'bar',
+                   '--config-file', paths[0],
+                   '--config-file', paths[1]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['b', 'a', 'r'])
+
+    def test_multistr_default(self):
+        self.conf.register_opt(MultiStrOpt('foo', default=['bar']))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['bar'])
+
+    def test_multistr_value(self):
+        self.conf.register_opt(MultiStrOpt('foo'))
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['bar'])
+
+    @unittest.skip('FIXME(markmc): values spread across the CLI and multiple '
+                   'config files should be appended')
+    def test_multistr_values_append(self):
+        self.conf.register_cli_opt(ListOpt('foo'))
+
+        paths = self.create_tempfiles([('1.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar\n'),
+                                       ('2.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = bar\n')])
+
+        self.conf(['--foo', 'bar',
+                   '--config-file', paths[0],
+                   '--config-file', paths[1]])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, ['bar', 'bar', 'bar'])
+
+
+class OptGroupsTestCase(BaseTestCase):
+
+    def test_arg_group(self):
+        blaa_group = OptGroup('blaa')
+        self.conf.register_group(blaa_group)
+        self.conf.register_cli_opt(StrOpt('foo'), group=blaa_group)
+
+        self.conf(['--blaa-foo', 'bar'])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+    def test_arg_group_by_name(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_cli_opt(StrOpt('foo'), group='blaa')
+
+        self.conf(['--blaa-foo', 'bar'])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+    def test_arg_group_with_default(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_cli_opt(StrOpt('foo', default='bar'), group='blaa')
+
+        self.conf([])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+    def test_arg_group_in_config_file(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_opt(StrOpt('foo'), group='blaa')
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[blaa]\n'
+                                        'foo = bar\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+
+class TemplateSubstitutionTestCase(BaseTestCase):
+
+    def _prep_test_str_sub(self, foo_default=None, bar_default=None):
+        self.conf.register_cli_opt(StrOpt('foo', default=foo_default))
+        self.conf.register_cli_opt(StrOpt('bar', default=bar_default))
+
+    def _assert_str_sub(self):
+        self.assertTrue(hasattr(self.conf, 'bar'))
+        self.assertEquals(self.conf.bar, 'blaa')
+
+    def test_str_sub_default_from_default(self):
+        self._prep_test_str_sub(foo_default='blaa', bar_default='$foo')
+
+        self.conf([])
+
+        self._assert_str_sub()
+
+    def test_str_sub_default_from_arg(self):
+        self._prep_test_str_sub(bar_default='$foo')
+
+        self.conf(['--foo', 'blaa'])
+
+        self._assert_str_sub()
+
+    def test_str_sub_default_from_config_file(self):
+        self._prep_test_str_sub(bar_default='$foo')
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = blaa\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self._assert_str_sub()
+
+    def test_str_sub_arg_from_default(self):
+        self._prep_test_str_sub(foo_default='blaa')
+
+        self.conf(['--bar', '$foo'])
+
+        self._assert_str_sub()
+
+    def test_str_sub_arg_from_arg(self):
+        self._prep_test_str_sub()
+
+        self.conf(['--foo', 'blaa', '--bar', '$foo'])
+
+        self._assert_str_sub()
+
+    def test_str_sub_arg_from_config_file(self):
+        self._prep_test_str_sub()
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'foo = blaa\n')])
+
+        self.conf(['--config-file', paths[0], '--bar=$foo'])
+
+        self._assert_str_sub()
+
+    def test_str_sub_config_file_from_default(self):
+        self._prep_test_str_sub(foo_default='blaa')
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'bar = $foo\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self._assert_str_sub()
+
+    def test_str_sub_config_file_from_arg(self):
+        self._prep_test_str_sub()
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'bar = $foo\n')])
+
+        self.conf(['--config-file', paths[0], '--foo=blaa'])
+
+        self._assert_str_sub()
+
+    def test_str_sub_config_file_from_config_file(self):
+        self._prep_test_str_sub()
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[DEFAULT]\n'
+                                        'bar = $foo\n'
+                                        'foo = blaa\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self._assert_str_sub()
+
+    def test_str_sub_group_from_default(self):
+        self.conf.register_cli_opt(StrOpt('foo', default='blaa'))
+        self.conf.register_group(OptGroup('ba'))
+        self.conf.register_cli_opt(StrOpt('r', default='$foo'), group='ba')
+
+        self.conf([])
+
+        self.assertTrue(hasattr(self.conf, 'ba'))
+        self.assertTrue(hasattr(self.conf.ba, 'r'))
+        self.assertEquals(self.conf.ba.r, 'blaa')
+
+
+class ReparseTestCase(BaseTestCase):
+
+    def test_reparse(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_cli_opt(StrOpt('foo', default='r'), group='blaa')
+
+        paths = self.create_tempfiles([('test.conf',
+                                        '[blaa]\n'
+                                        'foo = b\n')])
+
+        self.conf(['--config-file', paths[0]])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'b')
+
+        self.conf(['--blaa-foo', 'a'])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'a')
+
+        self.conf([])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertTrue(hasattr(self.conf.blaa, 'foo'))
+        self.assertEquals(self.conf.blaa.foo, 'r')
+
+
+class OverridesTestCase(BaseTestCase):
+
+    def test_no_default_override(self):
+        self.conf.register_opt(StrOpt('foo'))
+        self.conf([])
+        self.assertEquals(self.conf.foo, None)
+        self.conf.set_default('foo', 'bar')
+        self.assertEquals(self.conf.foo, 'bar')
+
+    def test_default_override(self):
+        self.conf.register_opt(StrOpt('foo', default='foo'))
+        self.conf([])
+        self.assertEquals(self.conf.foo, 'foo')
+        self.conf.set_default('foo', 'bar')
+        self.assertEquals(self.conf.foo, 'bar')
+        self.conf.set_default('foo', None)
+        self.assertEquals(self.conf.foo, 'foo')
+
+    def test_override(self):
+        self.conf.register_opt(StrOpt('foo'))
+        self.conf.set_override('foo', 'bar')
+        self.conf([])
+        self.assertEquals(self.conf.foo, 'bar')
+
+    def test_group_no_default_override(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_opt(StrOpt('foo'), group='blaa')
+        self.conf([])
+        self.assertEquals(self.conf.blaa.foo, None)
+        self.conf.set_default('foo', 'bar', group='blaa')
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+    def test_default_override(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_opt(StrOpt('foo', default='foo'), group='blaa')
+        self.conf([])
+        self.assertEquals(self.conf.blaa.foo, 'foo')
+        self.conf.set_default('foo', 'bar', group='blaa')
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+        self.conf.set_default('foo', None, group='blaa')
+        self.assertEquals(self.conf.blaa.foo, 'foo')
+
+    def test_override(self):
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_opt(StrOpt('foo'), group='blaa')
+        self.conf.set_override('foo', 'bar', group='blaa')
+        self.conf([])
+        self.assertEquals(self.conf.blaa.foo, 'bar')
+
+
+class SadPathTestCase(BaseTestCase):
+
+    def test_unknown_attr(self):
+        self.conf([])
+        self.assertFalse(hasattr(self.conf, 'foo'))
+        self.assertRaisesRegexp(NoSuchOptError, 'foo',
+                                getattr, self.conf, 'foo')
+
+    def test_unknown_group_attr(self):
+        self.conf.register_group(OptGroup('blaa'))
+
+        self.conf([])
+
+        self.assertTrue(hasattr(self.conf, 'blaa'))
+        self.assertFalse(hasattr(self.conf.blaa, 'foo'))
+        self.assertRaisesRegexp(NoSuchOptError, 'blaa.*foo',
+                                getattr, self.conf.blaa, 'foo')
+
+    def test_ok_duplicate(self):
+        opt = StrOpt('foo')
+        self.conf.register_cli_opt(opt)
+        self.conf.register_cli_opt(opt)
+
+        self.conf([])
+
+        self.assertTrue(hasattr(self.conf, 'foo'))
+        self.assertEquals(self.conf.foo, None)
+
+    def test_error_duplicate(self):
+        self.conf.register_cli_opt(StrOpt('foo'))
+        self.assertRaisesRegexp(DuplicateOptError, 'foo',
+                                self.conf.register_cli_opt,
+                                StrOpt('foo'))
+
+    def test_error_duplicate_with_different_dest(self):
+        self.conf.register_cli_opt(StrOpt('foo', dest='f'))
+        self.assertRaisesRegexp(DuplicateOptError, 'foo',
+                                self.conf.register_cli_opt,
+                                StrOpt('foo'))
+
+    def test_error_duplicate_short(self):
+        self.conf.register_cli_opt(StrOpt('foo', short='f'))
+        self.assertRaises(DuplicateOptError,
+                          self.conf.register_cli_opt,
+                          StrOpt('bar', short='f'))
+
+    def test_no_such_group(self):
+        self.assertRaisesRegexp(NoSuchGroupError, 'blaa',
+                                self.conf.register_cli_opt,
+                                StrOpt('foo'), group='blaa')
+
+    def test_already_parsed(self):
+        self.conf([])
+
+        self.assertRaises(ArgsAlreadyParsedError,
+                          self.conf.register_cli_opt, StrOpt('foo'))
+
+    def test_bad_cli_arg(self):
+        self.stubs.Set(sys, 'stderr', StringIO.StringIO())
+
+        self.assertRaisesRegexp(SystemExit, '2', self.conf, ['--foo'])
+
+        self.assertIn('error', sys.stderr.getvalue())
+        self.assertIn('--foo', sys.stderr.getvalue())
+
+    def _do_test_bad_cli_value(self, opt_class):
+        self.conf.register_cli_opt(opt_class('foo'))
+
+        self.stubs.Set(sys, 'stderr', StringIO.StringIO())
+
+        self.assertRaisesRegexp(SystemExit, '2', self.conf, ['--foo', 'bar'])
+
+        self.assertIn('foo', sys.stderr.getvalue())
+        self.assertIn('bar', sys.stderr.getvalue())
+
+    def test_bad_int_arg(self):
+        self._do_test_bad_cli_value(IntOpt)
+
+    def test_bad_float_arg(self):
+        self._do_test_bad_cli_value(FloatOpt)
+
+    def test_conf_file_not_found(self):
+        paths = self.create_tempfiles([('test.conf', '')])
+        os.remove(paths[0])
+        self.tempfiles.remove(paths[0])
+
+        self.assertRaisesRegexp(ConfigFilesNotFoundError, paths[0],
+                                self.conf, ['--config-file', paths[0]])
+
+    def test_conf_file_not_found(self):
+        paths = self.create_tempfiles([('test.conf', 'foo')])
+
+        self.assertRaisesRegexp(ConfigFileParseError, paths[0],
+                                self.conf, ['--config-file', paths[0]])
+
+    def _do_test_conf_file_bad_value(self, opt_class):
+        self.conf.register_opt(opt_class('foo'))
+
+    def test_conf_file_bad_bool(self):
+        self._do_test_conf_file_bad_value(BoolOpt)
+
+    def test_conf_file_bad_int(self):
+        self._do_test_conf_file_bad_value(IntOpt)
+
+    def test_conf_file_bad_float(self):
+        self._do_test_conf_file_bad_value(FloatOpt)
+
+    def test_str_sub_from_group(self):
+        self.conf.register_group(OptGroup('f'))
+        self.conf.register_cli_opt(StrOpt('oo', default='blaa'), group='f')
+        self.conf.register_cli_opt(StrOpt('bar', default='$f.oo'))
+
+        self.conf([])
+
+        self.assertFalse(hasattr(self.conf, 'bar'))
+        self.assertRaises(TemplateSubstitutionError, getattr, self.conf, 'bar')
+
+    def test_set_default_unknown_attr(self):
+        self.conf([])
+        self.assertRaisesRegexp(NoSuchOptError, 'foo',
+                                self.conf.set_default, 'foo', 'bar')
+
+    def test_set_default_unknown_group(self):
+        self.conf([])
+        self.assertRaisesRegexp(NoSuchGroupError, 'blaa',
+                                self.conf.set_default,
+                                'foo', 'bar', group='blaa')
+
+    def test_set_override_unknown_attr(self):
+        self.conf([])
+        self.assertRaisesRegexp(NoSuchOptError, 'foo',
+                                self.conf.set_override, 'foo', 'bar')
+
+    def test_set_override_unknown_group(self):
+        self.conf([])
+        self.assertRaisesRegexp(NoSuchGroupError, 'blaa',
+                                self.conf.set_override,
+                                'foo', 'bar', group='blaa')
+
+
+class OptDumpingTestCase(BaseTestCase):
+
+    class FakeLogger:
+
+        def __init__(self, test_case, expected_lvl):
+            self.test_case = test_case
+            self.expected_lvl = expected_lvl
+            self.logged = []
+
+        def log(self, lvl, fmt, *args):
+            self.test_case.assertEquals(lvl, self.expected_lvl)
+            self.logged.append(fmt % args)
+
+    def test_log_opt_values(self):
+        self.conf.register_cli_opt(StrOpt('foo'))
+        self.conf.register_group(OptGroup('blaa'))
+        self.conf.register_cli_opt(StrOpt('bar'), 'blaa')
+
+        self.conf(['--foo', 'this', '--blaa-bar', 'that'])
+
+        logger = self.FakeLogger(self, 666)
+
+        self.conf.log_opt_values(logger, 666)
+
+        self.assertEquals(logger.logged, [
+                "*" * 80,
+                "Configuration options gathered from:",
+                "command line args: ['--foo', 'this', '--blaa-bar', 'that']",
+                "config files: []",
+                "=" * 80,
+                "config_file                    = []",
+                "foo                            = this",
+                "blaa.bar                       = that",
+                "*" * 80,
+                ])
+
+
+class CommonOptsTestCase(BaseTestCase):
+
+    def setUp(self):
+        super(CommonOptsTestCase, self).setUp()
+        self.conf = CommonConfigOpts()
+
+    def test_debug_verbose(self):
+        self.conf(['--debug', '--verbose'])
+
+        self.assertEquals(self.conf.debug, True)
+        self.assertEquals(self.conf.verbose, True)
+
+    def test_logging_opts(self):
+        self.conf([])
+
+        self.assertIsNone(self.conf.log_config)
+        self.assertIsNone(self.conf.log_file)
+        self.assertIsNone(self.conf.log_dir)
+
+        self.assertEquals(self.conf.log_format,
+                          CommonConfigOpts.DEFAULT_LOG_FORMAT)
+        self.assertEquals(self.conf.log_date_format,
+                          CommonConfigOpts.DEFAULT_LOG_DATE_FORMAT)
+
+        self.assertEquals(self.conf.use_syslog, False)