Fix mask/unmask implementation (Thanks Michael Biebl)

Turns out that I mistakenly linked the same symlinks to /dev/null that
one would normally link to the service file, but mask links are
orthogonal to that. As an example, for rsyslog.service, the mask link is
/etc/systemd/system/rsyslog.service -> /dev/null, not
/etc/systemd/system/mult-user.targe.wants/rsyslog.service

fixes #714903

2 files changed, 32 insertions, 55 deletions

diff --git a/script/deb-systemd-helper b/script/deb-systemd-helper
index c11f30f..92290ae 100755
--- a/script/deb-systemd-helper
+++ b/script/deb-systemd-helper
@@ -93,7 +93,6 @@ 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.
@@ -372,67 +371,40 @@ sub rmdir_if_empty {
 sub mask_service {
     my ($scriptname, $service_path) = @_;
 
-    my $dsh_state = dsh_state_path($service_path);
-    my @entries = state_file_entries($dsh_state);
-    debug "Contents: " . Dumper(\@entries);
+    my $mask_link = '/etc/systemd/system/' . basename($service_path);
 
-    for my $service_link (@entries) {
-        my $statefile = $service_link;
-        $statefile =~ s,^/etc/systemd/system/,$masked_state_dir/,;
-        next if -e $statefile;
-
-        my $old_dest;
-        if (-l $service_link) {
-            $old_dest = readlink($service_link);
-            unlink($service_link);
-        } else {
-            make_path(dirname($service_link));
-        }
-        print STDERR "ln -s '/dev/null' '$service_link'\n" unless $quiet;
-        symlink('/dev/null', $service_link) or
-            error("unable to link $service_link to /dev/null: $!");
-        $changed_sth = 1;
+    if (-e $mask_link) {
+        # If the link already exists, don’t do anything.
+        return if -l $mask_link && readlink($mask_link) eq '/dev/null';
 
-        # Store the old destination of the symlink so that we can unmask
-        # properly later.
-        make_path(dirname($statefile));
-        open(my $fh, '>>', $statefile);
-        print $fh $old_dest if defined($old_dest);
-        close($fh);
+        # Otherwise, error out.
+        error("$mask_link already exists");
     }
+
+    make_path(dirname($mask_link));
+    print STDERR "ln -s '/dev/null' '$mask_link'\n" unless $quiet;
+    symlink('/dev/null', $mask_link) or
+        error("unable to link $mask_link to /dev/null: $!");
+    $changed_sth = 1;
 }
 
 sub unmask_service {
     my ($scriptname, $service_path) = @_;
 
-    my $dsh_state = dsh_state_path($service_path);
-    my @entries = state_file_entries($dsh_state);
-    debug "Contents: " . Dumper(\@entries);
-
-    for my $service_link (@entries) {
-        my $statefile = $service_link;
-        $statefile =~ s,^/etc/systemd/system/,$masked_state_dir/,;
-        next if ! -e $statefile;
-
-        my @entries = state_file_entries($statefile);
-
-        if (! -l $service_link || readlink($service_link) ne '/dev/null') {
-            debug "Not unmasking $service_link because it is not a link to /dev/null";
-            next;
-        }
-        unlink($service_link);
+    my $mask_link = '/etc/systemd/system/' . basename($service_path);
 
-        if (@entries > 0) {
-            my $service_path = $entries[0];
-            make_path(dirname($service_link));
-            print STDERR "ln -s '$service_path' '$service_link'\n" unless $quiet;
-            symlink($service_path, $service_link) or
-                error("unable to link $service_link to $service_path: $!");
-            $changed_sth = 1;
-        }
+    # Not masked? Nothing to do.
+    return unless -e $mask_link;
 
-        unlink($statefile);
+    if (! -l $mask_link || readlink($mask_link) ne '/dev/null') {
+        debug "Not unmasking $mask_link because it is not a link to /dev/null";
+        return;
     }
+
+    print STDERR "rm '$mask_link'\n" unless $quiet;
+    unlink($mask_link) or
+        error("unable to remove $mask_link: $!");
+    $changed_sth = 1;
 }
 
 my $result = GetOptions(
diff --git a/t/001-deb-systemd-helper.t b/t/001-deb-systemd-helper.t
index 9c1773f..3d9c3b3 100644
--- a/t/001-deb-systemd-helper.t
+++ b/t/001-deb-systemd-helper.t
@@ -180,11 +180,15 @@ is_debian_installed($random_unit);
 # ┃ Verify “mask” (when enabled) results in the symlink pointing to /dev/null ┃
 # ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
+my $mask_path = "/etc/systemd/system/$random_unit";
+ok(! -l $mask_path, 'mask link does not exist yet');
+
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh mask $random_unit");
-is(readlink($symlink_path), '/dev/null', 'service masked');
+ok(-l $mask_path, 'mask link exists');
+is(readlink($mask_path), '/dev/null', 'service masked');
 
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh unmask $random_unit");
-isnt(readlink($symlink_path), '/dev/null', 'service no longer masked');
+ok(! -e $mask_path, 'mask link does not exist anymore');
 
 # ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
 # ┃ Verify “mask” (when disabled) works the same way                          ┃
@@ -194,9 +198,10 @@ $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh disable $random_unit");
 ok(! -e $symlink_path, 'symlink no longer exists');
 
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh mask $random_unit");
-is(readlink($symlink_path), '/dev/null', 'service masked');
+ok(-l $mask_path, 'mask link exists');
+is(readlink($mask_path), '/dev/null', 'service masked');
 
 $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh unmask $random_unit");
-ok(! -e $symlink_path, 'symlink no longer exists');
+ok(! -e $mask_path, 'symlink no longer exists');
 
 done_testing;