Move the 'debug' sysctl tree under options SYSCTL_DEBUG. It generates

an inordinate amount of synchronous console output that is fairly
undesirable on slower serial console.  It's easily hit by accident
when frobbing other sysctls late at night.

sys/conf/NOTES

@@ -299,6 +299,14 @@ options 	DDB_NUMSYM
 #
 options 	GDB
 
+#
+# SYSCTL_DEBUG enables a 'sysctl' debug tree that can be used to dump the
+# contents of the registered sysctl nodes on the console.  It is disabled by
+# default because it generates excessively verbose consol output that can
+# interfere with serial console operation.
+#
+options 	SYSCTL_DEBUG
+
 #
 # KTRACE enables the system-call tracing facility ktrace(2).  To be more
 # SMP-friendly, KTRACE uses a worker thread to process most trace events

sys/conf/options

@@ -54,6 +54,7 @@ GDBSPEED	opt_gdb.h
 KDB		opt_global.h
 KDB_TRACE	opt_kdb.h
 KDB_UNATTENDED	opt_kdb.h
+SYSCTL_DEBUG	opt_sysctl.h
 
 # Miscellaneous options.
 ADAPTIVE_GIANT	opt_adaptive_mutexes.h

sys/kern/kern_sysctl.c

@@ -466,6 +466,7 @@ SYSINIT(sysctl, SI_SUB_KMEM, SI_ORDER_ANY, sysctl_register_all, 0);
  * {0,5,...}	return the description the "..." OID.
  */
 
+#ifdef SYSCTL_DEBUG
 static void
 sysctl_sysctl_debug_dump_node(struct sysctl_oid_list *l, int i)
 {
@@ -518,6 +519,7 @@ sysctl_sysctl_debug(SYSCTL_HANDLER_ARGS)
 
 SYSCTL_PROC(_sysctl, 0, debug, CTLTYPE_STRING|CTLFLAG_RD,
 	0, 0, sysctl_sysctl_debug, "-", "");
+#endif
 
 static int
 sysctl_sysctl_name(SYSCTL_HANDLER_ARGS)