snapshot: Fix snapshots filling up the disk

- Snapper's cleanup algorithms don't apply limits unless they are specified in
the form of ranges. Changed all limit values in the configuration to ranges.
- Also, all MIN_AGE values have been set to 0 to avoid the disk space filling up
in case of a large number of snapshots generated in a very short amount of time.
- FREE_LIMIT has been increased to 30% from the default 20% since backup
archives also take up disk space on the root partition.

Fixes #1435

Signed-off-by: Joseph Nuthalapati <njoseph@thoughtworks.com>
Reviewed-by: Sunil Mohan Adapa <sunil@medhas.org>

actions/snapshot

@@ -39,6 +39,9 @@ def parse_arguments():
     subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
 
     subparsers.add_parser('setup', help='Configure snapper')
+    subparsers.add_parser(
+        'migrate',
+        help='Migrate existing user configuration to the new format')
     subparsers.add_parser('list', help='List snapshots')
     subparsers.add_parser('create', help='Create snapshot')
     subparsers.add_parser('get-config', help='Configurations of snapshot')
@@ -85,11 +88,20 @@ def subcommand_setup(_):
 
 def _set_default_config():
     command = [
-        'snapper', 'set-config', 'TIMELINE_CREATE=yes',
+        'snapper',
-        'TIMELINE_LIMIT_HOURLY=10', 'TIMELINE_LIMIT_MONTHLY=2',
+        'set-config',
-        'TIMELINE_LIMIT_WEEKLY=2', 'TIMELINE_LIMIT_YEARLY=0',
+        'TIMELINE_CREATE=yes',
-        'TIMELINE_LIMIT_DAILY=3', 'NUMBER_MIN_AGE=1296000', 'NUMBER_LIMIT=0',
+        'TIMELINE_MIN_AGE=0',
-        'NUMBER_LIMIT_IMPORTANT=4-10'
+        'TIMELINE_LIMIT_HOURLY=0-10',
+        'TIMELINE_LIMIT_DAILY=0-3',
+        'TIMELINE_LIMIT_WEEKLY=0-2',
+        'TIMELINE_LIMIT_MONTHLY=0-2',
+        'TIMELINE_LIMIT_YEARLY=0-0',
+        'NUMBER_MIN_AGE=0',
+        'NUMBER_LIMIT=0-100',
+        'NUMBER_LIMIT_IMPORTANT=0-20',
+        'EMPTY_PRE_POST_MIN_AGE=0',
+        'FREE_LIMIT=0.3',
     ]
     subprocess.run(command, check=True)
 
@@ -223,7 +235,7 @@ def subcommand_set_config(arguments):
     subprocess.run(command, check=True)
 
 
-def subcommand_get_config(_):
+def _get_config():
     command = ['snapper', 'get-config']
     process = subprocess.run(command, stdout=subprocess.PIPE, check=True)
     lines = process.stdout.decode().splitlines()
@@ -231,9 +243,45 @@ def subcommand_get_config(_):
     for line in lines[2:]:
         parts = [part.strip() for part in line.split('|')]
         config[parts[0]] = parts[1]
+    return config
+
+
+def subcommand_get_config(_):
+    config = _get_config()
     print(json.dumps(config))
 
 
+def subcommand_migrate(_):
+    """Migrate existing user configuration for snapshots
+    to the new configuration format.
+    Add in version 4 of the snapshots module.
+    This command will not check or perform first setup steps.
+    """
+    config = _get_config()
+
+    def convert_to_range(key):
+        value = config[key]
+        value = value if '-' in value else '0-{}'.format(value)
+        return '{}={}'.format(key, value)
+
+    command = [
+        'snapper',
+        'set-config',
+        'TIMELINE_MIN_AGE=0',
+        convert_to_range('TIMELINE_LIMIT_HOURLY'),
+        convert_to_range('TIMELINE_LIMIT_DAILY'),
+        convert_to_range('TIMELINE_LIMIT_WEEKLY'),
+        convert_to_range('TIMELINE_LIMIT_MONTHLY'),
+        convert_to_range('TIMELINE_LIMIT_YEARLY'),
+        'NUMBER_MIN_AGE=0',
+        'NUMBER_LIMIT=0-100',
+        'NUMBER_LIMIT_IMPORTANT=0-20',
+        'EMPTY_PRE_POST_MIN_AGE=0',
+        'FREE_LIMIT=0.3',
+    ]
+    subprocess.run(command, check=True)
+
+
 def subcommand_kill_daemon(_):
     """Kill the snapper daemon.
 

plinth/modules/snapshot/__init__.py

@@ -28,7 +28,7 @@ from plinth.menu import main_menu
 
 from .manifest import backup
 
-version = 3
+version = 4
 
 managed_packages = ['snapper']
 
@@ -67,13 +67,16 @@ def init():
 def setup(helper, old_version=None):
     """Install and configure the module."""
     helper.install(managed_packages)
+    if old_version:
+        helper.call('post', actions.superuser_run, 'snapshot', ['migrate'])
+    else:
         helper.call('post', actions.superuser_run, 'snapshot', ['setup'])
 
 
 def load_augeas():
     """Initialize Augeas."""
-    aug = augeas.Augeas(
+    aug = augeas.Augeas(flags=augeas.Augeas.NO_LOAD +
-        flags=augeas.Augeas.NO_LOAD + augeas.Augeas.NO_MODL_AUTOLOAD)
+                        augeas.Augeas.NO_MODL_AUTOLOAD)
 
     # shell-script config file lens
     aug.set('/augeas/load/Shellvars/lens', 'Shellvars.lns')
@@ -96,21 +99,24 @@ def get_configuration():
     def get_boolean_choice(status):
         return ('yes', 'Enabled') if status else ('no', 'Disabled')
 
+    def get_max_from_range(key):
+        return output[key].split('-')[-1]
+
     return {
         'enable_timeline_snapshots':
             get_boolean_choice(output['TIMELINE_CREATE'] == 'yes'),
         'enable_software_snapshots':
             get_boolean_choice(is_apt_snapshots_enabled(aug)),
         'hourly_limit':
-            output['TIMELINE_LIMIT_HOURLY'],
+            get_max_from_range('TIMELINE_LIMIT_HOURLY'),
         'daily_limit':
-            output['TIMELINE_LIMIT_DAILY'],
+            get_max_from_range('TIMELINE_LIMIT_DAILY'),
         'weekly_limit':
-            output['TIMELINE_LIMIT_WEEKLY'],
+            get_max_from_range('TIMELINE_LIMIT_WEEKLY'),
-        'yearly_limit':
-            output['TIMELINE_LIMIT_YEARLY'],
         'monthly_limit':
-            output['TIMELINE_LIMIT_MONTHLY'],
+            get_max_from_range('TIMELINE_LIMIT_MONTHLY'),
+        'yearly_limit':
+            get_max_from_range('TIMELINE_LIMIT_YEARLY'),
         'number_min_age':
             round(int(output['NUMBER_MIN_AGE']) / 86400),
     }

plinth/modules/snapshot/views.py

@@ -98,13 +98,17 @@ def update_configuration(request, old_status, new_status):
     def make_config(args):
         key, stamp = args[0], args[1]
         if old_status[key] != new_status[key]:
+            if 'limit' in key:
+                return stamp.format('0-{}'.format(new_status[key]))
+            else:
                 return stamp.format(new_status[key])
         else:
             return None
 
     new_status['number_min_age'] = int(new_status['number_min_age']) * 86400
 
-    config = filter(None,
+    config = filter(
+        None,
         map(make_config, [
             ('enable_timeline_snapshots', 'TIMELINE_CREATE={}'),
             ('hourly_limit', 'TIMELINE_LIMIT_HOURLY={}'),
@@ -115,8 +119,7 @@ def update_configuration(request, old_status, new_status):
             ('number_min_age', 'NUMBER_MIN_AGE={}'),
         ]))
 
-    if old_status['enable_software_snapshots'] != new_status[
+    if old_status['enable_software_snapshots'] != new_status['enable_software_snapshots']:
-            'enable_software_snapshots']:
         if new_status['enable_software_snapshots'] == 'yes':
             actions.superuser_run('snapshot', ['disable-apt-snapshot', 'no'])
         else: