upgrades: Check for held freedombox package daily

Guard against removing a hold while the package manager is busy.

Test:
1. Place hold on freedombox package.
2. Wait 3 minutes in development mode.
   - Package is held.
3. Touch /var/lib/freedombox/package-held.
4. Wait 3 minutes in development mode.
   - Package is not held.
   - Flag is removed.

Signed-off-by: James Valleroy <jvalleroy@mailbox.org>

actions/packages

@@ -18,9 +18,8 @@ import apt.cache
 import apt_inst
 import apt_pkg
 from plinth import cfg
-from plinth.action_utils import apt_hold_freedombox, run_apt_command
-
-LOCK_FILE = '/var/lib/dpkg/lock'
+from plinth.action_utils import (apt_hold_freedombox, is_package_manager_busy,
+                                 run_apt_command)
 
 logger = logging.getLogger(__name__)
 
@@ -115,12 +114,10 @@ def _assert_managed_packages(module, packages):
 
 
 def subcommand_is_package_manager_busy(_):
-    """Return whether package manager is busy.
-    This command uses the `lsof` command to check whether the dpkg lock file
-    is open which indicates that the package manager is busy"""
-    try:
-        subprocess.check_output(['lsof', LOCK_FILE])
-    except subprocess.CalledProcessError:
+    """Check whether package manager is busy.
+
+    An exit code of zero indicates that package manager is busy."""
+    if not is_package_manager_busy():
         sys.exit(-1)
 
 

actions/upgrades

@@ -16,8 +16,8 @@ import time
 
 from plinth.action_utils import (apt_hold, apt_hold_flag, apt_hold_freedombox,
                                  apt_unhold_freedombox, debconf_set_selections,
-                                 run_apt_command, service_daemon_reload,
-                                 service_restart)
+                                 is_package_manager_busy, run_apt_command,
+                                 service_daemon_reload, service_restart)
 from plinth.modules.apache.components import check_url
 from plinth.modules.snapshot import (is_apt_snapshots_enabled, is_supported as
                                      snapshot_is_supported, load_augeas as
@@ -145,7 +145,7 @@ def _run():
 
     # In case freedombox package was left in held state by an
     # interrupted process, release it.
-    if apt_hold_flag.exists():
+    if apt_hold_flag.exists() and not is_package_manager_busy():
         apt_unhold_freedombox()
 
     subprocess.Popen(['systemctl', 'start', 'freedombox-manual-upgrade'],
@@ -538,6 +538,11 @@ def subcommand_start_dist_upgrade(arguments):
     Check if a new stable release is available, and start dist-upgrade process
     if updates are enabled.
     """
+    # In case freedombox package was left in held state by an
+    # interrupted process, release it.
+    if apt_hold_flag.exists() and not is_package_manager_busy():
+        apt_unhold_freedombox()
+
     upgrade_ready, reason = _check_dist_upgrade(arguments.test)
     if upgrade_ready:
         with open(DIST_UPGRADE_SERVICE_PATH, 'w') as service_file:

plinth/action_utils.py

@@ -460,3 +460,15 @@ def apt_unhold_freedombox():
     subprocess.check_call(['apt-mark', 'unhold', 'freedombox'])
     if apt_hold_flag.exists():
         apt_hold_flag.unlink()
+
+
+def is_package_manager_busy():
+    """Return whether package manager is busy.
+    This command uses the `lsof` command to check whether the dpkg lock file
+    is open which indicates that the package manager is busy"""
+    LOCK_FILE = '/var/lib/dpkg/lock'
+    try:
+        subprocess.check_output(['lsof', LOCK_FILE])
+        return True
+    except subprocess.CalledProcessError:
+        return False