d-s-h: implement mask and unmask commands

2 files changed, 112 insertions, 5 deletions

diff --git a/script/deb-systemd-helper b/script/deb-systemd-helper
index 62ffc79..ae83cfa 100755
--- a/script/deb-systemd-helper
+++ b/script/deb-systemd-helper
@@ -35,7 +35,7 @@ deb-systemd-helper - subset of systemctl for machines not running systemd
 
 =head1 SYNOPSIS
 
-B<deb-systemd-helper> enable|disable|is-enabled|was-enabled|debian-installed|update-state|reenable S<I<unit file> ...>
+B<deb-systemd-helper> enable|disable|mask|unmask|is-enabled|was-enabled|debian-installed|update-state|reenable S<I<unit file> ...>
 
 =head1 DESCRIPTION
 
@@ -47,6 +47,9 @@ package). On the first "enable", an state file is created which will be deleted
 upon "disable", but only when _DEB_SYSTEMD_HELPER_PURGE=1 to distinguish purge
 from remove.
 
+The "mask" action will keep state on whether the service was enabled/disabled
+before and will properly return to that state on "unmask".
+
 The "was-enabled" action is not present in systemctl, but is required in Debian
 so that we can figure out whether a service was enabled before we installed an
 updated service file. See http://bugs.debian.org/717603 for details.
@@ -89,7 +92,8 @@ use Getopt::Long; # in core since Perl 5
 use Data::Dumper;
 
 my $quiet = 0;
-my $state_dir = '/var/lib/systemd/deb-systemd-helper-enabled';
+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.
@@ -124,7 +128,7 @@ sub find_unit {
 
 sub dsh_state_path {
     my ($scriptname) = @_;
-    return $state_dir . '/' . basename($scriptname) . '.dsh-also';
+    return $enabled_state_dir . '/' . basename($scriptname) . '.dsh-also';
 }
 
 sub state_file_entries {
@@ -221,7 +225,7 @@ sub make_systemd_links {
         record_in_statefile($dsh_state, $service_link);
 
         my $statefile = $service_link;
-        $statefile =~ s,^/etc/systemd/system/,$state_dir/,;
+        $statefile =~ s,^/etc/systemd/system/,$enabled_state_dir/,;
         next if -e $statefile;
 
         if (! -l $service_link) {
@@ -321,7 +325,7 @@ sub remove_links {
         #   but not re-created when re-installing the package.
         if (is_purge() || -l $link) {
             my $link_state = $link;
-            $link_state =~ s,^/etc/systemd/system/,$state_dir/,;
+            $link_state =~ s,^/etc/systemd/system/,$enabled_state_dir/,;
             unlink($link_state);
         }
 
@@ -365,6 +369,66 @@ sub rmdir_if_empty {
     }
 }
 
+sub mask_service {
+    my ($scriptname, $service_path) = @_;
+
+    my @links = get_link_closure($scriptname, $service_path);
+    for my $link (@links) {
+        my $service_link = $link->{src};
+
+        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: $!");
+        $changed_sth = 1;
+
+        # Store the old destination of the symlink so that we can unmask
+        # properly later.
+        make_path(dirname($statefile));
+        open(my $fh, '>>', $statefile);
+        print $fh $old_dest if defined($old_dest);
+        close($fh);
+    }
+}
+
+sub unmask_service {
+    my ($scriptname, $service_path) = @_;
+
+    my @links = get_link_closure($scriptname, $service_path);
+    for my $link (@links) {
+        my $service_link = $link->{src};
+
+        my $statefile = $service_link;
+        $statefile =~ s,^/etc/systemd/system/,$masked_state_dir/,;
+        next if ! -e $statefile;
+
+        my @entries = state_file_entries($statefile);
+
+        unlink($service_link) if -l $service_link;
+
+        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: $!");
+            $changed_sth = 1;
+        }
+
+        unlink($statefile);
+    }
+}
+
 my $result = GetOptions(
     "quiet" => \$quiet,
 );
@@ -446,6 +510,14 @@ for my $scriptname (@ARGV) {
     if ($action eq 'enable') {
         make_systemd_links($scriptname, $service_path);
     }
+
+    if ($action eq 'mask') {
+        mask_service($scriptname, $service_path);
+    }
+
+    if ($action eq 'unmask') {
+        unmask_service($scriptname, $service_path);
+    }
 }
 
 # If we changed anything and this machine is running systemd, tell
diff --git a/t/001-deb-systemd-helper.t b/t/001-deb-systemd-helper.t
index c27408c..9c1773f 100644
--- a/t/001-deb-systemd-helper.t
+++ b/t/001-deb-systemd-helper.t
@@ -164,4 +164,39 @@ $retval = system("DPKG_MAINTSCRIPT_PACKAGE=test _DEB_SYSTEMD_HELPER_PURGE=1 $dsh
 
 isnt_enabled($random_unit);
 
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “enable” after purging does re-create the symlinks.                ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+ok(! -l $symlink_path, 'symlink does not exist yet');
+isnt_enabled($random_unit);
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh enable $random_unit");
+
+is_enabled($random_unit);
+is_debian_installed($random_unit);
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “mask” (when enabled) results in the symlink pointing to /dev/null ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh mask $random_unit");
+is(readlink($symlink_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');
+
+# ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+# ┃ Verify “mask” (when disabled) works the same way                          ┃
+# ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+
+$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');
+
+$retval = system("DPKG_MAINTSCRIPT_PACKAGE=test $dsh unmask $random_unit");
+ok(! -e $symlink_path, 'symlink no longer exists');
+
 done_testing;