Store masked state to respect user’s maskingdebian/1.10

We cannot just unconditionally unmask services on installation time,
otherwise “systemctl mask” executed by the user will be reversed.

To that end, files in /var/lib/systemd/deb-systemd-helper-masked/ signal
that d-s-h masked the service and is allowed to unmask it.

3 files changed, 37 insertions, 6 deletions

diff --git a/debian/init-system-helpers.postinst b/debian/init-system-helpers.postinst
index cbea846..6afcaec 100644
--- a/debian/init-system-helpers.postinst
+++ b/debian/init-system-helpers.postinst
@@ -9,12 +9,6 @@ if dpkg --compare-versions "$2" lt "1.9"; then
     fi
 fi
 
-if dpkg --compare-versions "$2" lt "1.10"; then
-    if [ -d /var/lib/systemd/deb-systemd-helper-masked ]; then
-        rm -rf /var/lib/systemd/deb-systemd-helper-masked
-    fi
-fi
-
 #DEBHELPER#
 
 exit 0
diff --git a/script/deb-systemd-helper b/script/deb-systemd-helper
index 92290ae..3adcd9d 100755
--- a/script/deb-systemd-helper
+++ b/script/deb-systemd-helper
@@ -93,6 +93,7 @@ use Data::Dumper;
 
 my $quiet = 0;
 my $enabled_state_dir = '/var/lib/systemd/deb-systemd-helper-enabled';
+my $masked_state_dir = '/var/lib/systemd/deb-systemd-helper-masked';
 
 # Globals are bad, but in this specific case, it really makes things much
 # easier to write and understand.
@@ -386,6 +387,16 @@ sub mask_service {
     symlink('/dev/null', $mask_link) or
         error("unable to link $mask_link to /dev/null: $!");
     $changed_sth = 1;
+
+    my $statefile = $mask_link;
+    $statefile =~ s,^/etc/systemd/system/,$masked_state_dir/,;
+
+    # Store the fact that we masked this service, so that we can unmask it on
+    # installation time. We cannot unconditionally unmask because that would
+    # interfere with the user’s decision to mask a service.
+    make_path(dirname($statefile));
+    open(my $fh, '>>', $statefile);
+    close($fh);
 }
 
 sub unmask_service {
@@ -401,10 +412,19 @@ sub unmask_service {
         return;
     }
 
+    my $statefile = $mask_link;
+    $statefile =~ s,^/etc/systemd/system/,$masked_state_dir/,;
+
+    if (! -e $statefile) {
+        debug "Not unmasking $mask_link because the state file $statefile does not exist";
+        return;
+    }
+
     print STDERR "rm '$mask_link'\n" unless $quiet;
     unlink($mask_link) or
         error("unable to remove $mask_link: $!");
     $changed_sth = 1;
+    unlink($statefile);
 }
 
 my $result = GetOptions(
diff --git a/t/001-deb-systemd-helper.t b/t/001-deb-systemd-helper.t
index 5bb9ecd..4d814ea 100644
--- a/t/001-deb-systemd-helper.t
+++ b/t/001-deb-systemd-helper.t
@@ -191,4 +191,21 @@ is(readlink($mask_path), '/dev/null', 'service masked');
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh unmask $random_unit");
 ok(! -e $mask_path, 'symlink no longer exists');
 
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “mask”/unmask don’t do anything when the user already masked.      ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+ok(! -l $mask_path, 'mask link does not exist yet');
+symlink('/dev/null', $mask_path);
+ok(-l $mask_path, 'mask link exists');
+is(readlink($mask_path), '/dev/null', 'service masked');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh mask $random_unit");
+ok(-l $mask_path, 'mask link exists');
+is(readlink($mask_path), '/dev/null', 'service still masked');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh unmask $random_unit");
+ok(-l $mask_path, 'mask link exists');
+is(readlink($mask_path), '/dev/null', 'service still masked');
+
 done_testing;