containers: systemd exits with non-zero code

When a systemd service running in a container exits with a non-zero
code, it can be useful to terminate the container immediately and get
the exit code back to the host, when systemd-nspawn returns. This was
not possible to do. This patch adds the following to make it possible:

- Add a read-only "ExitCode" property on PID 1's "Manager" bus object.
  By default, it is 0 so the behaviour stays the same as previously.
- Add a method "SetExitCode" on the same object. The method fails when
  called on baremetal: it is only allowed in containers or in user
  session.
- Add support in systemctl to call "systemctl exit 42". It reuses the
  existing code for user session.
- Add exit.target and systemd-exit.service to the system instance.
- Change main() to actually call systemd-shutdown to exit() with the
  correct value.
- Add verb 'exit' in systemd-shutdown with parameter --exit-code
- Update systemctl manpage.

I used the following to test it:

| $ sudo rkt --debug --insecure-skip-verify run \
|            --mds-register=false --local docker://busybox \
|            --exec=/bin/chroot -- /proc/1/root \
|            systemctl --force exit 42
| ...
| Container rkt-895a0cba-5c66-4fa5-831c-e3f8ddc5810d failed with error code 42.
| $ echo $?
| 42

Fixes https://github.com/systemd/systemd/issues/1290

1 files changed, 14 insertions, 7 deletions

diff --git a/src/core/main.c b/src/core/main.c
index 200fe740da..9b59648279 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -1254,6 +1254,7 @@ int main(int argc, char *argv[]) {
         char *switch_root_dir = NULL, *switch_root_init = NULL;
         struct rlimit saved_rlimit_nofile = RLIMIT_MAKE_CONST(0);
         const char *error_message = NULL;
+        uint8_t shutdown_exit_code = 0;
 
 #ifdef HAVE_SYSV_COMPAT
         if (getpid() != 1 && strstr(program_invocation_short_name, "init")) {
@@ -1764,11 +1765,6 @@ int main(int argc, char *argv[]) {
 
                 switch (m->exit_code) {
 
-                case MANAGER_EXIT:
-                        retval = EXIT_SUCCESS;
-                        log_debug("Exit.");
-                        goto finish;
-
                 case MANAGER_RELOAD:
                         log_info("Reloading.");
 
@@ -1810,11 +1806,13 @@ int main(int argc, char *argv[]) {
                         log_notice("Switching root.");
                         goto finish;
 
+                case MANAGER_EXIT:
                 case MANAGER_REBOOT:
                 case MANAGER_POWEROFF:
                 case MANAGER_HALT:
                 case MANAGER_KEXEC: {
                         static const char * const table[_MANAGER_EXIT_CODE_MAX] = {
+                                [MANAGER_EXIT] = "exit",
                                 [MANAGER_REBOOT] = "reboot",
                                 [MANAGER_POWEROFF] = "poweroff",
                                 [MANAGER_HALT] = "halt",
@@ -1836,8 +1834,10 @@ int main(int argc, char *argv[]) {
 finish:
         pager_close();
 
-        if (m)
+        if (m) {
                 arg_shutdown_watchdog = m->shutdown_watchdog;
+                shutdown_exit_code = m->return_value;
+        }
         m = manager_free(m);
 
         for (j = 0; j < ELEMENTSOF(arg_default_rlimit); j++)
@@ -1978,7 +1978,8 @@ finish:
 
         if (shutdown_verb) {
                 char log_level[DECIMAL_STR_MAX(int) + 1];
-                const char* command_line[9] = {
+                char exit_code[DECIMAL_STR_MAX(uint8_t) + 1];
+                const char* command_line[11] = {
                         SYSTEMD_SHUTDOWN_BINARY_PATH,
                         shutdown_verb,
                         "--log-level", log_level,
@@ -2015,6 +2016,12 @@ finish:
                 if (log_get_show_location())
                         command_line[pos++] = "--log-location";
 
+                if (streq(shutdown_verb, "exit")) {
+                        command_line[pos++] = "--exit-code";
+                        command_line[pos++] = exit_code;
+                        xsprintf(exit_code, "%d", shutdown_exit_code);
+                }
+
                 assert(pos < ELEMENTSOF(command_line));
 
                 if (arm_reboot_watchdog && arg_shutdown_watchdog > 0) {