From ae12603a54610248b25dd74cf2d544c0a9d741fa Mon Sep 17 00:00:00 2001
From: Sascha Wildner <saw@online.de>
Date: Mon, 14 Jan 2019 18:59:58 +0100
Subject: [PATCH] kernel: Hide the sysctl.debug sysctl in the SYSCTL_DEBUG
 kernel option.

The output is quite excessive and was previously too easily triggered,
like with "sysctl name=value" (instead of just "name=value") in
/etc/sysctl.conf.

Taken-from: FreeBSD
---
 sys/conf/options       | 3 +++
 sys/config/LINT64      | 8 ++++++++
 sys/kern/kern_sysctl.c | 4 ++++
 3 files changed, 15 insertions(+)

diff --git a/sys/conf/options b/sys/conf/options
index 2a8228d7fd..75c7b63a5d 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -673,6 +673,9 @@ PANIC_REBOOT_WAIT_TIME	opt_panic.h
 EVDEV_SUPPORT		opt_evdev.h
 EVDEV_DEBUG		opt_evdev.h
 
+# Sysctl debugging
+SYSCTL_DEBUG		opt_sysctl.h
+
 # Obsolete options (will be removed in the future)
 #
 FAST_IPSEC		opt_dontuse.h
diff --git a/sys/config/LINT64 b/sys/config/LINT64
index 51a6184914..c1db0db7ea 100644
--- a/sys/config/LINT64
+++ b/sys/config/LINT64
@@ -199,6 +199,14 @@ options 	INVARIANTS
 #
 options 	DIAGNOSTIC
 
+#
+# 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 console output that can
+# interfere with serial console operation.
+#
+options 	SYSCTL_DEBUG
+
 #
 # This option let some drivers co-exist that can't co-exist in a running
 # system.  This is used to be able to compile all kernel code in one go for
diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index da0692ffc3..6d261003e0 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -51,6 +51,8 @@
 #include <vm/vm.h>
 #include <vm/vm_extern.h>
 
+#include "opt_sysctl.h"
+
 static MALLOC_DEFINE(M_SYSCTL, "sysctl", "sysctl internal magic");
 static MALLOC_DEFINE(M_SYSCTLOID, "sysctloid", "sysctl dynamic oids");
 
@@ -524,6 +526,7 @@ sysctl_register_all(void *arg)
 }
 SYSINIT(sysctl, SI_BOOT1_POST, SI_ORDER_ANY, sysctl_register_all, 0);
 
+#ifdef SYSCTL_DEBUG
 /*
  * "Staff-functions"
  *
@@ -605,6 +608,7 @@ sysctl_sysctl_debug(SYSCTL_HANDLER_ARGS)
 
 SYSCTL_PROC(_sysctl, 0, debug, CTLTYPE_STRING | CTLFLAG_RD,
 	    0, 0, sysctl_sysctl_debug, "-", "");
+#endif /* SYSCTL_DEBUG */
 
 static int
 sysctl_sysctl_name(SYSCTL_HANDLER_ARGS)
-- 
2.41.0