systemctl: automatically softreboot/kexec if set up on reboot

Automatically softreboot if the nextroot has been set up with an OS
tree, or automatically kexec if a kernel has been loaded with kexec
--load.

Add SYSTEMCTL_SKIP_AUTO_KEXEC and SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT to
skip the automated switchover.

src/systemctl/systemctl-logind.c

@@ -80,7 +80,12 @@ int logind_reboot(enum action a) {
                 return 0;
 
         SET_FLAG(flags, SD_LOGIND_ROOT_CHECK_INHIBITORS, arg_check_inhibitors > 0);
-        SET_FLAG(flags, SD_LOGIND_REBOOT_VIA_KEXEC, a == ACTION_KEXEC);
+        SET_FLAG(flags,
+                 SD_LOGIND_REBOOT_VIA_KEXEC,
+                 a == ACTION_KEXEC || (a == ACTION_REBOOT && getenv_bool("SYSTEMCTL_SKIP_AUTO_KEXEC") <= 0));
+        SET_FLAG(flags,
+                 SD_LOGIND_SOFT_REBOOT_IF_NEXTROOT_SET_UP,
+                 a == ACTION_REBOOT && getenv_bool("SYSTEMCTL_SKIP_AUTO_SOFT_REBOOT") <= 0);
         SET_FLAG(flags, SD_LOGIND_SOFT_REBOOT, a == ACTION_SOFT_REBOOT);
 
         r = bus_call_method(bus, bus_login_mgr, method_with_flags, &error, NULL, "t", flags);

src/systemctl/systemctl.c

@@ -1090,10 +1090,7 @@ int systemctl_dispatch_parse_argv(int argc, char *argv[]) {
                 return halt_parse_argv(argc, argv);
 
         } else if (invoked_as(argv, "reboot")) {
-                if (kexec_loaded())
-                        arg_action = ACTION_KEXEC;
-                else
-                        arg_action = ACTION_REBOOT;
+                arg_action = ACTION_REBOOT;
                 return halt_parse_argv(argc, argv);
 
         } else if (invoked_as(argv, "shutdown")) {