logind: add Halt() and CanHalt() APIs

This adds new method calls Halt() and CanHalt() to the logind bus APIs.
They aren't overly useful (as the whole concept of halting isn't really
too useful), however they clean up one major asymmetry: currently, using
the "shutdown" legacy commands it is possibly to enqueue a "halt"
operation through logind, while logind officially doesn't actually
support this. Moreover, the path through "shutdown" currently ultimately
fails, since the referenced "halt" action isn't actually defined in
PolicyKit.

Finally, the current logic results in an unexpected asymmetry in
systemctl: "systemctl poweroff", "systemctl reboot" are currently
asynchronous (due to the logind involvement) while "systemctl halt"
isnt. Let's clean this up, and make all three APIs implemented by
logind natively, and all three hence asynchronous in "systemctl".

Moreover, let's add the missing PK action.

Fixes: #6957

src/login/logind-dbus.c

@@ -1409,12 +1409,12 @@ static int bus_manager_log_shutdown(
         if (streq(unit_name, SPECIAL_POWEROFF_TARGET)) {
                 p = "MESSAGE=System is powering down";
                 q = "SHUTDOWN=power-off";
-        } else if (streq(unit_name, SPECIAL_HALT_TARGET)) {
-                p = "MESSAGE=System is halting";
-                q = "SHUTDOWN=halt";
         } else if (streq(unit_name, SPECIAL_REBOOT_TARGET)) {
                 p = "MESSAGE=System is rebooting";
                 q = "SHUTDOWN=reboot";
+        } else if (streq(unit_name, SPECIAL_HALT_TARGET)) {
+                p = "MESSAGE=System is halting";
+                q = "SHUTDOWN=halt";
         } else if (streq(unit_name, SPECIAL_KEXEC_TARGET)) {
                 p = "MESSAGE=System is rebooting with kexec";
                 q = "SHUTDOWN=kexec";
@@ -1822,6 +1822,20 @@ static int method_reboot(sd_bus_message *message, void *userdata, sd_bus_error *
                         error);
 }
 
+static int method_halt(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Manager *m = userdata;
+
+        return method_do_shutdown_or_sleep(
+                        m, message,
+                        SPECIAL_HALT_TARGET,
+                        INHIBIT_SHUTDOWN,
+                        "org.freedesktop.login1.halt",
+                        "org.freedesktop.login1.halt-multiple-sessions",
+                        "org.freedesktop.login1.halt-ignore-inhibit",
+                        NULL,
+                        error);
+}
+
 static int method_suspend(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         Manager *m = userdata;
 
@@ -1911,9 +1925,12 @@ fail:
 }
 
 static void reset_scheduled_shutdown(Manager *m) {
+        assert(m);
+
         m->scheduled_shutdown_timeout_source = sd_event_source_unref(m->scheduled_shutdown_timeout_source);
         m->wall_message_timeout_source = sd_event_source_unref(m->wall_message_timeout_source);
         m->nologin_timeout_source = sd_event_source_unref(m->nologin_timeout_source);
+
         m->scheduled_shutdown_type = mfree(m->scheduled_shutdown_type);
         m->scheduled_shutdown_timeout = 0;
         m->shutdown_dry_run = false;
@@ -1922,6 +1939,7 @@ static void reset_scheduled_shutdown(Manager *m) {
                 (void) unlink("/run/nologin");
                 m->unlink_nologin = false;
         }
+
         (void) unlink("/run/systemd/shutdown/scheduled");
 }
 
@@ -1940,12 +1958,14 @@ static int manager_scheduled_shutdown_handler(
         if (isempty(m->scheduled_shutdown_type))
                 return 0;
 
-        if (streq(m->scheduled_shutdown_type, "halt"))
-                target = SPECIAL_HALT_TARGET;
-        else if (streq(m->scheduled_shutdown_type, "poweroff"))
+        if (streq(m->scheduled_shutdown_type, "poweroff"))
                 target = SPECIAL_POWEROFF_TARGET;
-        else
+        else if (streq(m->scheduled_shutdown_type, "reboot"))
                 target = SPECIAL_REBOOT_TARGET;
+        else if (streq(m->scheduled_shutdown_type, "halt"))
+                target = SPECIAL_HALT_TARGET;
+        else
+                assert_not_reached("unexpected shutdown type");
 
         /* Don't allow multiple jobs being executed at the same time */
         if (m->action_what) {
@@ -2002,7 +2022,11 @@ static int method_schedule_shutdown(sd_bus_message *message, void *userdata, sd_
                 m->shutdown_dry_run = true;
         }
 
-        if (streq(type, "reboot")) {
+        if (streq(type, "poweroff")) {
+                action = "org.freedesktop.login1.power-off";
+                action_multiple_sessions = "org.freedesktop.login1.power-off-multiple-sessions";
+                action_ignore_inhibit = "org.freedesktop.login1.power-off-ignore-inhibit";
+        } else if (streq(type, "reboot")) {
                 action = "org.freedesktop.login1.reboot";
                 action_multiple_sessions = "org.freedesktop.login1.reboot-multiple-sessions";
                 action_ignore_inhibit = "org.freedesktop.login1.reboot-ignore-inhibit";
@@ -2010,10 +2034,6 @@ static int method_schedule_shutdown(sd_bus_message *message, void *userdata, sd_
                 action = "org.freedesktop.login1.halt";
                 action_multiple_sessions = "org.freedesktop.login1.halt-multiple-sessions";
                 action_ignore_inhibit = "org.freedesktop.login1.halt-ignore-inhibit";
-        } else if (streq(type, "poweroff")) {
-                action = "org.freedesktop.login1.power-off";
-                action_multiple_sessions = "org.freedesktop.login1.power-off-multiple-sessions";
-                action_ignore_inhibit = "org.freedesktop.login1.power-off-ignore-inhibit";
         } else
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Unsupported shutdown type");
 
@@ -2260,6 +2280,19 @@ static int method_can_reboot(sd_bus_message *message, void *userdata, sd_bus_err
                         error);
 }
 
+static int method_can_halt(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Manager *m = userdata;
+
+        return method_can_shutdown_or_sleep(
+                        m, message,
+                        INHIBIT_SHUTDOWN,
+                        "org.freedesktop.login1.halt",
+                        "org.freedesktop.login1.halt-multiple-sessions",
+                        "org.freedesktop.login1.halt-ignore-inhibit",
+                        NULL,
+                        error);
+}
+
 static int method_can_suspend(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         Manager *m = userdata;
 
@@ -2612,11 +2645,13 @@ const sd_bus_vtable manager_vtable[] = {
         SD_BUS_METHOD("FlushDevices", "b", NULL, method_flush_devices, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("PowerOff", "b", NULL, method_poweroff, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("Reboot", "b", NULL, method_reboot, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("Halt", "b", NULL, method_halt, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("Suspend", "b", NULL, method_suspend, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("Hibernate", "b", NULL, method_hibernate, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("HybridSleep", "b", NULL, method_hybrid_sleep, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CanPowerOff", NULL, "s", method_can_poweroff, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CanReboot", NULL, "s", method_can_reboot, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("CanHalt", NULL, "s", method_can_halt, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CanSuspend", NULL, "s", method_can_suspend, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CanHibernate", NULL, "s", method_can_hibernate, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("CanHybridSleep", NULL, "s", method_can_hybrid_sleep, SD_BUS_VTABLE_UNPRIVILEGED),

src/login/org.freedesktop.login1.conf

@@ -132,6 +132,10 @@
                        send_interface="org.freedesktop.login1.Manager"
                        send_member="Reboot"/>
 
+                <allow send_destination="org.freedesktop.login1"
+                       send_interface="org.freedesktop.login1.Manager"
+                       send_member="Halt"/>
+
                 <allow send_destination="org.freedesktop.login1"
                        send_interface="org.freedesktop.login1.Manager"
                        send_member="Suspend"/>
@@ -152,6 +156,10 @@
                        send_interface="org.freedesktop.login1.Manager"
                        send_member="CanReboot"/>
 
+                <allow send_destination="org.freedesktop.login1"
+                       send_interface="org.freedesktop.login1.Manager"
+                       send_member="CanHalt"/>
+
                 <allow send_destination="org.freedesktop.login1"
                        send_interface="org.freedesktop.login1.Manager"
                        send_member="CanSuspend"/>

src/login/org.freedesktop.login1.policy.in

@@ -218,6 +218,39 @@
                 <annotate key="org.freedesktop.policykit.imply">org.freedesktop.login1.reboot</annotate>
         </action>
 
+        <action id="org.freedesktop.login1.halt">
+                <_description>Halt the system</_description>
+                <_message>Authentication is required for halting the system.</_message>
+                <defaults>
+                        <allow_any>auth_admin_keep</allow_any>
+                        <allow_inactive>auth_admin_keep</allow_inactive>
+                        <allow_active>auth_admin_keep</allow_active>
+                </defaults>
+                <annotate key="org.freedesktop.policykit.imply">org.freedesktop.login1.set-wall-message</annotate>
+        </action>
+
+        <action id="org.freedesktop.login1.halt-multiple-sessions">
+                <_description>Halt the system while other users are logged in</_description>
+                <_message>Authentication is required for halting the system while other users are logged in.</_message>
+                <defaults>
+                        <allow_any>auth_admin_keep</allow_any>
+                        <allow_inactive>auth_admin_keep</allow_inactive>
+                        <allow_active>auth_admin_keep</allow_active>
+                </defaults>
+                <annotate key="org.freedesktop.policykit.imply">org.freedesktop.login1.halt</annotate>
+        </action>
+
+        <action id="org.freedesktop.login1.halt-ignore-inhibit">
+                <_description>Halt the system while an application asked to inhibit it</_description>
+                <_message>Authentication is required for halting the system while an application asked to inhibit it.</_message>
+                <defaults>
+                        <allow_any>auth_admin_keep</allow_any>
+                        <allow_inactive>auth_admin_keep</allow_inactive>
+                        <allow_active>auth_admin_keep</allow_active>
+                </defaults>
+                <annotate key="org.freedesktop.policykit.imply">org.freedesktop.login1.halt</annotate>
+        </action>
+
         <action id="org.freedesktop.login1.suspend">
                 <_description>Suspend the system</_description>
                 <_message>Authentication is required for suspending the system.</_message>

src/systemctl/systemctl.c

@@ -3267,14 +3267,19 @@ static int logind_reboot(enum action a) {
 
         switch (a) {
 
+        case ACTION_POWEROFF:
+                method = "PowerOff";
+                description = "power off system";
+                break;
+
         case ACTION_REBOOT:
                 method = "Reboot";
                 description = "reboot system";
                 break;
 
-        case ACTION_POWEROFF:
-                method = "PowerOff";
-                description = "power off system";
+        case ACTION_HALT:
+                method = "Halt";
+                description = "halt system";
                 break;
 
         case ACTION_SUSPEND:
@@ -3568,6 +3573,7 @@ static int start_special(int argc, char *argv[], void *userdata) {
                 if (IN_SET(a,
                            ACTION_POWEROFF,
                            ACTION_REBOOT,
+                           ACTION_HALT,
                            ACTION_SUSPEND,
                            ACTION_HIBERNATE,
                            ACTION_HYBRID_SLEEP)) {
@@ -8503,7 +8509,7 @@ static int halt_main(void) {
                 /* Try logind if we are a normal user and no special
                  * mode applies. Maybe PolicyKit allows us to shutdown
                  * the machine. */
-                if (IN_SET(arg_action, ACTION_POWEROFF, ACTION_REBOOT)) {
+                if (IN_SET(arg_action, ACTION_POWEROFF, ACTION_REBOOT, ACTION_HALT)) {
                         r = logind_reboot(arg_action);
                         if (r >= 0)
                                 return r;