minidlna: Move sysctl config to /etc/sysctl.d/50-freedombox.conf

/etc/sysctl.conf is owned by procps package.

Test: Run minidlna install on fresh image.
- /etc/sysctl.conf is not modified.
- /etc/sysctl.d/50-freedombox.conf has the expected content.
- /proc/sys/fs/inotify/max_user_watches contains 100000.

- Running with these changes upgrades app version and triggers a setup. Changes
in /etc/sysctl.conf are removed. After undoing the changes /etc/sysctl.conf is
identical to pristine version installed from procps package. This can be
obtained by running; rm -f /etc/sysctl.conf ; apt install --reinstall procps -o
Dpkg::Options::=--force-confmiss

Closes #1802.

Signed-off-by: James Valleroy <jvalleroy@mailbox.org>
[sunil: Undo changes done in /etc/sysctl.conf in older versions]
[sunil: Increment app version to trigger configuration migration]
[sunil: Ensure that app is not re-enabled during migration]
Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

actions/minidlna

@@ -15,6 +15,11 @@ from plinth.utils import grep
 
 CONFIG_PATH = '/etc/minidlna.conf'
 
+SYSCTL_CONF = '''# This file is managed and overwritten by FreedomBox.
+# Helps minidlna monitor changes in large media directories
+fs.inotify.max_user_watches = 100000
+'''
+
 
 def parse_arguments():
     """Return parsed command line arguments as dictionary."""
@@ -33,19 +38,34 @@ def parse_arguments():
     return parser.parse_args()
 
 
+def _undo_old_configuration_changes():
+    """Restore /etc/sysctl.conf to before our changes.
+
+    Older version of minidlna app in FreedomBox < 20.9 wrote to
+    /etc/sysctl.conf directly. This will cause conffile prompt during upgrade
+    of procps package. Undo the changes so that upgrade can happen smoothly.
+
+    """
+    aug = augeas.Augeas(flags=augeas.Augeas.NO_LOAD +
+                        augeas.Augeas.NO_MODL_AUTOLOAD)
+    aug.set('/augeas/load/Sysctl/lens', 'Sysctl.lns')
+    aug.set('/augeas/load/Sysctl/incl[last() + 1]', '/etc/sysctl.conf')
+    aug.load()
+
+    key_path = '/files/etc/sysctl.conf/fs.inotify.max_user_watches'
+    if aug.get(key_path) == '100000':
+        aug.remove(key_path)
+        aug.save()
+
+
 def subcommand_setup(arguments):
     """
     Increase inotify watches per folder to allow minidlna to
     monitor changes in large media-dirs.
     """
-    aug = augeas.Augeas(
-        flags=augeas.Augeas.NO_LOAD + augeas.Augeas.NO_MODL_AUTOLOAD)
-    aug.set('/augeas/load/Sysctl/lens', 'Sysctl.lns')
-    aug.set('/augeas/load/Sysctl/incl[last() + 1]', '/etc/sysctl.conf')
-    aug.load()
-
-    aug.set('/files/etc/sysctl.conf/fs.inotify.max_user_watches', '100000')
-    aug.save()
+    _undo_old_configuration_changes()
+    with open('/etc/sysctl.d/50-freedombox-minidlna.conf', 'w') as conf:
+        conf.write(SYSCTL_CONF)
 
     subprocess.run(['systemctl', 'restart', 'systemd-sysctl'], check=True)
 

plinth/modules/minidlna/__init__.py

@@ -13,7 +13,7 @@ from plinth.modules.users.components import UsersAndGroups
 
 from .manifest import backup, clients  # noqa
 
-version = 1
+version = 2
 
 managed_packages = ['minidlna']
 
@@ -94,4 +94,5 @@ def setup(helper, old_version=None):
     """Install and configure the package"""
     helper.install(managed_packages)
     helper.call('post', actions.superuser_run, 'minidlna', ['setup'])
-    helper.call('post', app.enable)
+    if not old_version:
+        helper.call('post', app.enable)