systemctl: show reverse dependencies or before/after ordering

Also update completion scripts a bit.

man/systemctl.xml

@@ -142,6 +142,29 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>.
         </listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><option>--reverse</option></term>
+
+        <listitem>
+          <para>Show reverse dependencies between units with
+          <command>list-dependencies</command>, i.e. units with
+          dependencies of type <varname>Wants=</varname> or
+          <varname>Requires=</varname> on the given unit.
+          </para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><option>--after</option></term>
+        <term><option>--before</option></term>
+
+        <listitem>
+          <para>Show which units are started after, resp. before
+          with <command>list-dependencies</command>.
+          </para>
+        </listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><option>--failed</option></term>
 

shell-completion/bash/systemctl

@@ -70,7 +70,7 @@ _systemctl () {
         local i verb comps mode
 
         local -A OPTS=(
-               [STANDALONE]='--all -a --defaults --fail --ignore-dependencies --failed --force -f --full --global
+               [STANDALONE]='--all -a --reverse --after --before --defaults --fail --ignore-dependencies --failed --force -f --full --global
                              --help -h --no-ask-password --no-block --no-legend --no-pager --no-reload --no-wall
                              --quiet -q --privileged -P --system --user --version --runtime'
                       [ARG]='--host -H --kill-mode --kill-who --property -p --signal -s --type -t --root'
@@ -117,7 +117,7 @@ _systemctl () {
         fi
 
         local -A VERBS=(
-                [ALL_UNITS]='is-active is-failed is-enabled status show mask preset help'
+                [ALL_UNITS]='is-active is-failed is-enabled status show mask preset help list-dependencies'
             [ENABLED_UNITS]='disable'
            [DISABLED_UNITS]='enable'
         [REENABLABLE_UNITS]='reenable'

shell-completion/systemd-zsh-completion.zsh

@@ -12,6 +12,9 @@ _ctls()
                 {-t,--type=}'[List only units of a particular type]:unit type:(automount device mount path service snapshot socket swap target timer)' \
                 \*{-p,--property=}'[Show only properties by specific name]:unit property' \
                 {-a,--all}'[Show all units/properties, including dead/empty ones]' \
+                '--reverse[Show reverse dependencies]' \
+                '--after[Show units ordered after]' \
+                '--before[Show units ordered before]' \
                 '--failed[Show only failed units]' \
                 "--full[Don't ellipsize unit names on output]" \
                 '--fail[When queueing a new job, fail if conflicting jobs are pending]' \
@@ -348,6 +351,8 @@ _outputmodes() {
     "disable:Disable one or more unit files"
     "reenable:Reenable one or more unit files"
     "preset:Enable/disable one or more unit files based on preset configuration"
+    "help:Show documentation for specified units"
+    "list-dependencies:Show unit dependency tree"
     "mask:Mask one or more units"
     "unmask:Unmask one or more units"
     "link:Link one or more units files into the search path"
@@ -462,7 +467,7 @@ _systemctl_disabled_units(){_sys_disabled_units=($(__systemctl list-unit-files
 _systemctl_masked_units()  {_sys_masked_units=(  $(__systemctl list-unit-files     | { while read a b; do [[ $b == "masked" ]] && echo " $a"; done; }) )}
 
 # Completion functions for ALL_UNITS
-for fun in is-active is-failed is-enabled status show mask preset ; do
+for fun in is-active is-failed is-enabled status show mask preset help list-dependencies ; do
   (( $+functions[_systemctl_$fun] )) || _systemctl_$fun()
   {
     _systemctl_really_all_units

src/systemctl/systemctl.c

@@ -72,6 +72,12 @@ static char **arg_types = NULL;
 static char **arg_load_states = NULL;
 static char **arg_properties = NULL;
 static bool arg_all = false;
+static enum dependency {
+        DEPENDENCY_FORWARD,
+        DEPENDENCY_REVERSE,
+        DEPENDENCY_AFTER,
+        DEPENDENCY_BEFORE,
+} arg_dependency = DEPENDENCY_FORWARD;
 static const char *arg_job_mode = "replace";
 static UnitFileScope arg_scope = UNIT_FILE_SYSTEM;
 static bool arg_no_block = false;
@@ -979,12 +985,19 @@ static int list_dependencies_print(const char *name, int level, unsigned int bra
 }
 
 static int list_dependencies_get_dependencies(DBusConnection *bus, const char *name, char ***deps) {
-        static const char dependencies[] =
-                "Requires\0"
-                "RequiresOverridable\0"
-                "Requisite\0"
-                "RequisiteOverridable\0"
-                "Wants\0";
+        static const char *dependencies[] = {
+                [DEPENDENCY_FORWARD] = "Requires\0"
+                                       "RequiresOverridable\0"
+                                       "Requisite\0"
+                                       "RequisiteOverridable\0"
+                                       "Wants\0",
+                [DEPENDENCY_REVERSE] = "RequiredBy\0"
+                                       "RequiredByOverridable\0"
+                                       "WantedBy\0"
+                                       "PartOf\0",
+                [DEPENDENCY_AFTER]   = "After\0",
+                [DEPENDENCY_BEFORE]  = "Before\0",
+        };
 
         _cleanup_free_ char *path;
         const char *interface = "org.freedesktop.systemd1.Unit";
@@ -1049,7 +1062,8 @@ static int list_dependencies_get_dependencies(DBusConnection *bus, const char *n
                 dbus_message_iter_recurse(&sub2, &sub3);
                 dbus_message_iter_next(&sub);
 
-                if (!nulstr_contains(dependencies, prop))
+                assert(arg_dependency < ELEMENTSOF(dependencies));
+                if (!nulstr_contains(dependencies[arg_dependency], prop))
                         continue;
 
                 if (dbus_message_iter_get_arg_type(&sub3) == DBUS_TYPE_ARRAY) {
@@ -4479,6 +4493,7 @@ static int systemctl_help(void) {
                "  -a --all            Show all loaded units/properties, including dead/empty\n"
                "                      ones. To list all units installed on the system, use\n"
                "                      the 'list-unit-files' command instead.\n"
+               "     --reverse        Show reverse dependencies with 'list-dependencies'\n"
                "     --failed         Show only failed units\n"
                "     --full           Don't ellipsize unit names on output\n"
                "     --fail           When queueing a new job, fail if conflicting jobs are\n"
@@ -4544,7 +4559,8 @@ static int systemctl_help(void) {
                "  unset-cgroup [NAME] [CGROUP...] Remove unit from a control group\n"
                "  load [NAME...]                  Load one or more units\n"
                "  list-dependencies [NAME]        Recursively show units which are required\n"
-               "                                  or wanted by this unit\n\n"
+               "                                  or wanted by this unit or by which this\n"
+               "                                  unit is required or wanted\n\n"
                "Unit File Commands:\n"
                "  list-unit-files                 List installed unit files\n"
                "  enable [NAME...]                Enable one or more unit files\n"
@@ -4680,6 +4696,9 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
 
         enum {
                 ARG_FAIL = 0x100,
+                ARG_REVERSE,
+                ARG_AFTER,
+                ARG_BEFORE,
                 ARG_SHOW_TYPES,
                 ARG_IRREVERSIBLE,
                 ARG_IGNORE_DEPENDENCIES,
@@ -4707,6 +4726,9 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                 { "type",      required_argument, NULL, 't'           },
                 { "property",  required_argument, NULL, 'p'           },
                 { "all",       no_argument,       NULL, 'a'           },
+                { "reverse",   no_argument,       NULL, ARG_REVERSE   },
+                { "after",     no_argument,       NULL, ARG_AFTER     },
+                { "before",    no_argument,       NULL, ARG_BEFORE    },
                 { "show-types", no_argument,      NULL, ARG_SHOW_TYPES },
                 { "failed",    no_argument,       NULL, ARG_FAILED    },
                 { "full",      no_argument,       NULL, ARG_FULL      },
@@ -4829,6 +4851,18 @@ static int systemctl_parse_argv(int argc, char *argv[]) {
                         arg_all = true;
                         break;
 
+                case ARG_REVERSE:
+                        arg_dependency = DEPENDENCY_REVERSE;
+                        break;
+
+                case ARG_AFTER:
+                        arg_dependency = DEPENDENCY_AFTER;
+                        break;
+
+                case ARG_BEFORE:
+                        arg_dependency = DEPENDENCY_BEFORE;
+                        break;
+
                 case ARG_SHOW_TYPES:
                         arg_show_types = true;
                         break;