shutdown: convert to VERB_COMMAND and add --introspect-cli

systemd-shutdown parsed a bunch of options, but had no way to print
them. Add the standard --help and --version options and the CLI
introspection.

parse_argv() is moved before the PID 1 check, so that the new options
also work when the binary is invoked manually. As PID 1 we can never
return from main() (the kernel would panic), so in that case parse
errors still freeze(), and the help output is followed by a freeze()
too. Ctrl-Alt-Delete and console reopening are re-enabled before
freezing, so that the freeze can be escaped through the kernel and the
error is visible, as before.

The --help/--version/introspect-cli option names are already listed in
the kernel command line exclusion list in proc-cmdline.c.

src/shutdown/shutdown.c

@@ -16,6 +16,7 @@
 #include "alloc-util.h"
 #include "async.h"
 #include "binfmt-util.h"
+#include "build.h"
 #include "cgroup-setup.h"
 #include "cgroup-util.h"
 #include "constants.h"
@@ -49,6 +50,7 @@
 #include "terminal-util.h"
 #include "time-util.h"
 #include "umount.h"
+#include "verbs.h"
 #include "virt.h"
 #include "watchdog.h"
 
@@ -60,6 +62,13 @@ static const char *arg_verb = NULL;
 static uint8_t arg_exit_code = 0;
 static usec_t arg_timeout = DEFAULT_TIMEOUT_USEC;
 
+COMMAND(
+        "systemd-shutdown\0",
+        "Execute the final phase of system shutdown.",
+        .argspec = "reboot|poweroff|halt|kexec|exit\0",
+        .man_pages = "systemd-shutdown.8\0",
+);
+
 static int parse_argv(int argc, char *argv[]) {
         assert(argc >= 1);
         assert(argv);
@@ -75,6 +84,15 @@ static int parse_argv(int argc, char *argv[]) {
         FOREACH_OPTION_OR_RETURN(c, &opts)
                 switch (c) {
 
+                OPTION_COMMON_HELP:
+                        return command_print_help();
+
+                OPTION_COMMON_VERSION:
+                        return version();
+
+                OPTION_COMMON_INTROSPECT_CLI:
+                        return introspect_cli(SD_JSON_FORMAT_OFF);
+
                 OPTION_COMMON_LOG_LEVEL:
                         r = log_set_max_level_from_string(opts.arg);
                         if (r < 0)
@@ -149,7 +167,7 @@ static int parse_argv(int argc, char *argv[]) {
         if (!arg_verb)
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Verb argument missing.");
 
-        return 0;
+        return 1; /* Further action */
 }
 
 static int switch_root_initramfs(void) {
@@ -403,9 +421,17 @@ static int run(int argc, char *argv[]) {
         log_set_prohibit_ipc(true);
         log_parse_environment();
 
-        if (getpid_cached() != 1)
+        r = parse_argv(argc, argv);
+        if (getpid_cached() != 1) {
+                /* If we're a normal user space process, our work is done. Either we hit an error, or were
+                 * called with --help, --version, or another option that was handled by parse_argv(), or it
+                 * looks like we're being asked to do some real work, but we should do that only as part of
+                 * the real shutdown sequence. */
+                if (r <= 0)
+                        return r;
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                        "Not executed by init (PID 1). Refusing to operate.");
+        }
 
         log_set_always_reopen_console(true);
 
@@ -414,8 +440,7 @@ static int run(int argc, char *argv[]) {
          * through kernel. */
         (void) reboot(RB_ENABLE_CAD);
 
-        r = parse_argv(argc, argv);
-        if (r < 0)
+        if (r <= 0)
                 goto error;
 
         log_open();
@@ -711,9 +736,14 @@ static int run(int argc, char *argv[]) {
         r = log_error_errno(errno, "Failed to invoke reboot(): %m");
 
 error:
-        log_struct_errno(LOG_EMERG, r,
-                         LOG_MESSAGE("Critical error while doing system shutdown: %m"),
-                         LOG_MESSAGE_ID(SD_MESSAGE_SHUTDOWN_ERROR_STR));
+        if (r == 0)
+                log_struct(LOG_EMERG,
+                           LOG_MESSAGE("Non-shutdown operation requested, cannot operate."),
+                           LOG_MESSAGE_ID(SD_MESSAGE_SHUTDOWN_ERROR_STR));
+        else
+                log_struct_errno(LOG_EMERG, r,
+                                 LOG_MESSAGE("Critical error while doing system shutdown: %m"),
+                                 LOG_MESSAGE_ID(SD_MESSAGE_SHUTDOWN_ERROR_STR));
         freeze();
 }
 

test/units/TEST-74-AUX-UTILS.introspect-cli.sh

@@ -115,6 +115,7 @@ INTROSPECTABLE=(
     systemd-resolved
     systemd-run
     systemd-sbsign
+    systemd-shutdown
     systemd-sleep
     systemd-socket-activate
     systemd-socket-proxyd