From 45a1a30ecec2c0e3bb0bb1b93a0608e1ffcdf9c4 Mon Sep 17 00:00:00 2001
From: robert <robert@openbsd.org>
Date: Mon, 7 Nov 2022 14:25:44 +0000
Subject: [PATCH] introduce a new kern.autoconf_serial sysctl that can be used
 by userland to monitor state changes of the kernel device tree

input from dnd ok dlg@, deraadt@
---
 sys/kern/kern_sysctl.c   | 4 +++-
 sys/kern/subr_autoconf.c | 9 ++++++++-
 sys/sys/sysctl.h         | 6 ++++--
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index abf9cf0ded7..ff42ebb5129 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sysctl.c,v 1.407 2022/11/05 19:29:46 cheloha Exp $	*/
+/*	$OpenBSD: kern_sysctl.c,v 1.408 2022/11/07 14:25:44 robert Exp $	*/
 /*	$NetBSD: kern_sysctl.c,v 1.17 1996/05/20 17:49:05 mrg Exp $	*/
 
 /*-
@@ -126,6 +126,7 @@ extern long numvnodes;
 extern int allowdt;
 extern int audio_record_enable;
 extern int video_record_enable;
+extern int autoconf_serial;
 
 int allowkmem;
 
@@ -341,6 +342,7 @@ const struct sysctl_bounded_args kern_vars[] = {
 #ifdef PTRACE
 	{KERN_GLOBAL_PTRACE, &global_ptrace, 0, 1},
 #endif
+	{KERN_AUTOCONF_SERIAL, &autoconf_serial, SYSCTL_INT_READONLY},
 };
 
 int
diff --git a/sys/kern/subr_autoconf.c b/sys/kern/subr_autoconf.c
index a35b2224724..41633140dc6 100644
--- a/sys/kern/subr_autoconf.c
+++ b/sys/kern/subr_autoconf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_autoconf.c,v 1.96 2022/04/07 09:37:32 tb Exp $	*/
+/*	$OpenBSD: subr_autoconf.c,v 1.97 2022/11/07 14:25:44 robert Exp $	*/
 /*	$NetBSD: subr_autoconf.c,v 1.21 1996/04/04 06:06:18 cgd Exp $	*/
 
 /*
@@ -106,6 +106,11 @@ struct mutex autoconf_attdet_mtx = MUTEX_INITIALIZER(IPL_HIGH);
  */
 int	autoconf_attdet;
 
+/*
+ * Versioned state of the devices tree so that changes can be detected.
+ */
+unsigned int autoconf_serial = 0;
+
 /*
  * Initialize autoconfiguration data structures.  This occurs before console
  * initialization as that might require use of this subsystem.  Furthermore
@@ -419,6 +424,7 @@ config_attach(struct device *parent, void *match, void *aux, cfprint_t print)
 	mtx_enter(&autoconf_attdet_mtx);
 	if (--autoconf_attdet == 0)
 		wakeup(&autoconf_attdet);
+	autoconf_serial++;
 	mtx_leave(&autoconf_attdet_mtx);
 	return (dev);
 }
@@ -642,6 +648,7 @@ done:
 	mtx_enter(&autoconf_attdet_mtx);
 	if (++autoconf_attdet == 0)
 		wakeup(&autoconf_attdet);
+	autoconf_serial++;
 	mtx_leave(&autoconf_attdet_mtx);
 	return (rv);
 }
diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index 84564782931..4fa5afdf6c8 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sysctl.h,v 1.230 2022/11/05 19:29:46 cheloha Exp $	*/
+/*	$OpenBSD: sysctl.h,v 1.231 2022/11/07 14:25:44 robert Exp $	*/
 /*	$NetBSD: sysctl.h,v 1.16 1996/04/09 20:55:36 cgd Exp $	*/
 
 /*
@@ -192,7 +192,8 @@ struct ctlname {
 #define	KERN_UTC_OFFSET		88	/* int: adjust RTC time to UTC */
 #define	KERN_VIDEO		89	/* struct: video properties */
 #define	KERN_CLOCKINTR		90	/* node: clockintr */
-#define	KERN_MAXID		91	/* number of valid kern ids */
+#define	KERN_AUTOCONF_SERIAL	91	/* int: kernel device tree state serial */
+#define	KERN_MAXID		92	/* number of valid kern ids */
 
 #define	CTL_KERN_NAMES { \
 	{ 0, 0 }, \
@@ -286,6 +287,7 @@ struct ctlname {
 	{ "utc_offset", CTLTYPE_INT }, \
 	{ "video", CTLTYPE_STRUCT }, \
  	{ "clockintr", CTLTYPE_NODE }, \
+	{ "autoconf_serial", CTLTYPE_INT }, \
 }
 
 /*
-- 
2.20.1