Introduce a snapper plugin for yum

Provides automatic pre/post snapshots for each yum transaction,
just like the official plugin for zypper (SUSE systems).

Related: rockstor#1432

base-buildout.cfg

@@ -230,8 +230,9 @@ input = ${buildout:directory}/conf/settings.conf.in
 
 [snapper-conf]
 recipe = plone.recipe.command
-location = /etc/snapper/config-templates/default
 command =
-    cp ${buildout:directory}/conf/snapper-default-config ${:location}
+    cp -f ${buildout:directory}/conf/snapper-default-config /etc/snapper/config-templates/default
     [ -f /etc/snapper/configs/root ] || snapper create-config /
+    cp -f ${buildout:directory}/conf/yum_snapper.py /usr/lib/yum-plugins
+    cp -f ${buildout:directory}/conf/yum_snapper.conf /etc/yum/pluginconf.d
 update-command = ${:command}

conf/yum_snapper.conf

@@ -0,0 +1,5 @@
+[main]
+enabled=1
+# Transactions starting with these patterns will have their snapshots marked
+# as important
+important=kernel-,dracut,glibc,systemd,udev,snapper

conf/yum_snapper.py

@@ -0,0 +1,89 @@
+"""
+This plugin creates snapper pre and post snapshots upon modifications by yum.
+"""
+
+from os import readlink, getppid
+from os.path import basename
+from dbus import SystemBus, Interface, DBusException
+from yum.plugins import PluginYumExit, TYPE_CORE
+import logging
+
+"""
+Copyright (c) 2016 RockStor, Inc. <http://rockstor.com>
+This file is part of RockStor.
+
+RockStor 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.
+
+RockStor 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, see <http://www.gnu.org/licenses/>.
+"""
+
+# Yum
+requires_api_version = '2.7'
+plugin_type = (TYPE_CORE,)
+
+# Own global variables
+snapper = None
+description = ''
+pre_number = None
+important = []
+cleanup = 'number'
+userdata = {'important': 'no'}
+
+
+def init_hook(conduit):
+    """Set up global settings for the other hooks.
+    """
+    global important, description, snapper
+    important = conduit.confList('main', 'important', [])
+    description = 'yum(%s)' % basename(readlink('/proc/%d/exe' % getppid()))
+    try:
+        bus = SystemBus()
+        snapper = Interface(bus.get_object('org.opensuse.Snapper',
+                                           '/org/opensuse/Snapper'),
+                            dbus_interface='org.opensuse.Snapper')
+    except DBusException as e:
+        message = 'Could not connect to snapperd:\n  %s' % e
+        raise PluginYumExit(message)
+
+
+def pretrans_hook(conduit):
+    """Take a snapper pre snapshot, which is marked as important depending on
+    patterns specified in yum_snapper.conf.
+    """
+    global userdata, pre_number
+    transaction = conduit.getTsInfo()
+    for name in {item.name for item in transaction}:
+        if any(name.startswith(item) for item in important):
+            userdata['important'] = 'yes'
+            break
+    try:
+        logging.info('Creating pre snapshot')
+        pre_number = snapper.CreatePreSnapshot('root', description, cleanup,
+                                               userdata)
+        logging.debug('Created pre snapshot %d' % pre_number)
+    except DBusException as e:
+        logging.error('Pre snapshot creation failed:')
+        logging.error(' %s' % e)
+
+
+def posttrans_hook(conduit):
+    """Take a snapper post snapshot if the pre snapshot exists.
+    """
+    if pre_number:
+        try:
+            logging.info('Creating post snapshot')
+            post_number = snapper.CreatePostSnapshot('root', pre_number, '',
+                                                     cleanup, userdata)
+            logging.debug('Created post snapshot %d' % post_number)
+        except DBusException as e:
+            logging.error('Post snapshot creation failed:')
+            logging.error(' %s' % e)