Add new module freezer

Sometimes we need to have a static picture of the repositories
and packages installed in a system, so we can install new transient
packages (and the dependencies) and be able to go back to a previous
state where those packages are not there anymore.

This module allows the user to take this picture, and revert all
the changes done after this picture. We can remove package,
reinstall packages that are missing, and do the same for repositories.

salt/modules/freezer.py

@@ -0,0 +1,294 @@
+# -*- coding: utf-8 -*-
+#
+# Author: Alberto Planas <aplanas@suse.com>
+#
+# Copyright 2018 SUSE LINUX GmbH, Nuernberg, Germany.
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+'''
+:maintainer:    Alberto Planas <aplanas@suse.com>
+:maturity:      new
+:depends:       None
+:platform:      Linux
+'''
+from __future__ import absolute_import, print_function, unicode_literals
+import logging
+import os
+
+from salt.exceptions import CommandExecutionError
+from salt.utils.args import clean_kwargs
+from salt.utils.files import fopen
+import salt.utils.json as json
+from salt.ext.six.moves import zip
+
+log = logging.getLogger(__name__)
+
+__func_alias__ = {
+    'list_': 'list',
+}
+
+
+def __virtual__():
+    '''
+    Freezer is based on top of the pkg module.
+
+    Return True as pkg is going to be there, so we can avoid of
+    loading all modules.
+
+    '''
+    return True
+
+
+def _states_path():
+    '''
+    Return the path where we will store the states.
+    '''
+    return os.path.join(__opts__['cachedir'], 'freezer')
+
+
+def _paths(name=None):
+    '''
+    Return the full path for the packages and repository freezer
+    files.
+
+    '''
+    name = 'freezer' if not name else name
+    states_path = _states_path()
+    return (
+        os.path.join(states_path, '{}-pkgs.yml'.format(name)),
+        os.path.join(states_path, '{}-reps.yml'.format(name)),
+    )
+
+
+def status(name=None):
+    '''
+    Return True if there is already a frozen state.
+
+    A frozen state is merely a list of packages (including the
+    version) in a specific time. This information can be used to
+    compare with the current list of packages, and revert the
+    installation of some extra packages that are in the system.
+
+    name
+        Name of the frozen state. Optional.
+
+    CLI Example:
+
+    .. code-block:: bash
+
+        salt '*' freezer.status
+        salt '*' freezer.status pre_install
+
+    '''
+    name = 'freezer' if not name else name
+    return all(os.path.isfile(i) for i in _paths(name))
+
+
+def list_():
+    '''
+    Return the list of frozen states.
+
+    CLI Example:
+
+    .. code-block:: bash
+
+        salt '*' freezer.list
+
+    '''
+    ret = []
+    states_path = _states_path()
+    if not os.path.isdir(states_path):
+        return ret
+
+    for state in os.listdir(states_path):
+        if state.endswith(('-pkgs.yml', '-reps.yml')):
+            # Remove the suffix, as both share the same size
+            ret.append(state[:-9])
+    return sorted(set(ret))
+
+
+def freeze(name=None, force=False, **kwargs):
+    '''
+    Save the list of package and repos in a freeze file.
+
+    As this module is build on top of the pkg module, the user can
+    send extra attributes to the underlying pkg module via kwargs.
+    This function will call ``pkg.list_pkgs`` and ``pkg.list_repos``,
+    and any additional arguments will be passed through to those
+    functions.
+
+    name
+        Name of the frozen state. Optional.
+
+    force
+        If true, overwrite the state. Optional.
+
+    CLI Example:
+
+    .. code-block:: bash
+
+        salt '*' freezer.freeze
+        salt '*' freezer.freeze pre_install
+        salt '*' freezer.freeze force=True root=/chroot
+
+    '''
+    states_path = _states_path()
+
+    try:
+        os.makedirs(states_path)
+    except OSError as e:
+        msg = 'Error when trying to create the freezer storage %s: %s'
+        log.error(msg, states_path, e)
+        raise CommandExecutionError(msg % (states_path, e))
+
+    if status(name) and not force:
+        raise CommandExecutionError('The state is already present. Use '
+                                    'force parameter to overwrite.')
+    safe_kwargs = clean_kwargs(**kwargs)
+    pkgs = __salt__['pkg.list_pkgs'](**safe_kwargs)
+    repos = __salt__['pkg.list_repos'](**safe_kwargs)
+    for name, content in zip(_paths(name), (pkgs, repos)):
+        with fopen(name, 'w') as fp:
+            json.dump(content, fp)
+    return True
+
+
+def restore(name=None, **kwargs):
+    '''
+    Make sure that the system contains the packages and repos from a
+    frozen state.
+
+    Read the list of packages and repositories from the freeze file,
+    and compare it with the current list of packages and repos. If
+    there is any difference, all the missing packages are repos will
+    be installed, and all the extra packages and repos will be
+    removed.
+
+    As this module is build on top of the pkg module, the user can
+    send extra attributes to the underlying pkg module via kwargs.
+    This function will call ``pkg.list_repos``, ``pkg.mod_repo``,
+    ``pkg.list_pkgs``, ``pkg.install``, ``pkg.remove`` and
+    ``pkg.del_repo``, and any additional arguments will be passed
+    through to those functions.
+
+    name
+        Name of the frozen state. Optional.
+
+    CLI Example:
+
+    .. code-block:: bash
+
+        salt '*' freezer.restore
+        salt '*' freezer.restore root=/chroot
+
+    '''
+    if not status(name):
+        raise CommandExecutionError('Frozen state not found.')
+
+    frozen_pkgs = {}
+    frozen_repos = {}
+    for name, content in zip(_paths(name), (frozen_pkgs, frozen_repos)):
+        with fopen(name) as fp:
+            content.update(json.load(fp))
+
+    # The ordering of removing or adding packages and repos can be
+    # relevant, as maybe some missing package comes from a repo that
+    # is also missing, so it cannot be installed. But can also happend
+    # that a missing package comes from a repo that is present, but
+    # will be removed.
+    #
+    # So the proposed order is;
+    #   - Add missing repos
+    #   - Add missing packages
+    #   - Remove extra packages
+    #   - Remove extra repos
+
+    safe_kwargs = clean_kwargs(**kwargs)
+
+    # Note that we expect that the information stored in list_XXX
+    # match with the mod_XXX counterpart. If this is not the case the
+    # recovery will be partial.
+
+    res = {
+        'pkgs': {'add': [], 'remove': []},
+        'repos': {'add': [], 'remove': []},
+        'comment': [],
+    }
+
+    # Add missing repositories
+    repos = __salt__['pkg.list_repos'](**safe_kwargs)
+    missing_repos = set(frozen_repos) - set(repos)
+    for repo in missing_repos:
+        try:
+            # In Python 2 we cannot do advance destructuring, so we
+            # need to create a temporary dictionary that will merge
+            # all the parameters
+            _tmp_kwargs = frozen_repos[repo].copy()
+            _tmp_kwargs.update(safe_kwargs)
+            __salt__['pkg.mod_repo'](repo, **_tmp_kwargs)
+            res['repos']['add'].append(repo)
+            log.info('Added missing repository %s', repo)
+        except Exception as e:
+            msg = 'Error adding %s repository: %s'
+            log.error(msg, repo, e)
+            res['comment'].append(msg % (repo, e))
+
+    # Add missing packages
+    # NOTE: we can remove the `for` using `pkgs`. This will improve
+    # performance, but I want to have a more detalied report of what
+    # packages are installed or failled.
+    pkgs = __salt__['pkg.list_pkgs'](**safe_kwargs)
+    missing_pkgs = set(frozen_pkgs) - set(pkgs)
+    for pkg in missing_pkgs:
+        try:
+            __salt__['pkg.install'](name=pkg, **safe_kwargs)
+            res['pkgs']['add'].append(pkg)
+            log.info('Added missing package %s', pkg)
+        except Exception as e:
+            msg = 'Error adding %s package: %s'
+            log.error(msg, pkg, e)
+            res['comment'].append(msg % (pkg, e))
+
+    # Remove extra packages
+    pkgs = __salt__['pkg.list_pkgs'](**safe_kwargs)
+    extra_pkgs = set(pkgs) - set(frozen_pkgs)
+    for pkg in extra_pkgs:
+        try:
+            __salt__['pkg.remove'](name=pkg, **safe_kwargs)
+            res['pkgs']['remove'].append(pkg)
+            log.info('Removed extra package %s', pkg)
+        except Exception as e:
+            msg = 'Error removing %s package: %s'
+            log.error(msg, pkg, e)
+            res['comment'].append(msg % (pkg, e))
+
+    # Remove extra repositories
+    repos = __salt__['pkg.list_repos'](**safe_kwargs)
+    extra_repos = set(repos) - set(frozen_repos)
+    for repo in extra_repos:
+        try:
+            __salt__['pkg.del_repo'](repo, **safe_kwargs)
+            res['repos']['remove'].append(repo)
+            log.info('Removed extra repository %s', repo)
+        except Exception as e:
+            msg = 'Error removing %s repository: %s'
+            log.error(msg, repo, e)
+            res['comment'].append(msg % (repo, e))
+
+    return res