pid1: add new mode systemd.show-status=error and use it when 'quiet' is passed

systemd.show-status=error is useful for the case where people care about errors
only.

If people want to have a quiet boot, they most likely don't want to see all
status output even if there is a delay in boot, so make "quiet" imply
systemd.show-status=error instead of systemd.show-status=auto.

Fixes #14976.

src/core/main.c

@@ -494,7 +494,7 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
         } else if (streq(key, "quiet") && !value) {
 
                 if (arg_show_status == _SHOW_STATUS_INVALID)
-                        arg_show_status = SHOW_STATUS_AUTO;
+                        arg_show_status = SHOW_STATUS_ERROR;
 
         } else if (streq(key, "debug") && !value) {
 

src/core/manager.c

@@ -4085,7 +4085,7 @@ void manager_recheck_journal(Manager *m) {
 
 void manager_set_show_status(Manager *m, ShowStatus mode, const char *reason) {
         assert(m);
-        assert(IN_SET(mode, SHOW_STATUS_AUTO, SHOW_STATUS_NO, SHOW_STATUS_YES, SHOW_STATUS_TEMPORARY));
+        assert(mode >= 0 && mode < _SHOW_STATUS_MAX);
 
         if (!MANAGER_IS_SYSTEM(m))
                 return;

src/core/show-status.c

@@ -16,6 +16,7 @@
 
 static const char* const show_status_table[_SHOW_STATUS_MAX] = {
         [SHOW_STATUS_NO]        = "no",
+        [SHOW_STATUS_ERROR]     = "error",
         [SHOW_STATUS_AUTO]      = "auto",
         [SHOW_STATUS_TEMPORARY] = "temporary",
         [SHOW_STATUS_YES]       = "yes",

src/core/show-status.h

@@ -9,6 +9,7 @@
 
 typedef enum ShowStatus {
         SHOW_STATUS_NO,         /* printing of status is disabled */
+        SHOW_STATUS_ERROR,      /* only print errors */
         SHOW_STATUS_AUTO,       /* disabled but may flip to _TEMPORARY */
         SHOW_STATUS_TEMPORARY,  /* enabled temporarily, may flip back to _AUTO */
         SHOW_STATUS_YES,        /* printing of status is enabled */