Index: sys/conf/options
===================================================================
--- sys/conf/options
+++ sys/conf/options
@@ -178,6 +178,7 @@
 NO_ADAPTIVE_RWLOCKS
 NO_ADAPTIVE_SX
 NO_EVENTTIMERS		opt_timer.h
+NO_OBSOLETE_CODE	opt_global.h
 NO_SYSCTL_DESCR	opt_global.h
 NSWBUF_MIN	opt_swap.h
 MBUF_PACKET_ZONE_DISABLE	opt_global.h
Index: sys/kern/subr_bus.c
===================================================================
--- sys/kern/subr_bus.c
+++ sys/kern/subr_bus.c
@@ -5604,6 +5604,56 @@
 	    UID_ROOT, GID_WHEEL, 0600, "devctl2");
 }
 
+/*
+ * Obsolete management stuff.
+ */
+static int obsolete_panic = 0;
+/* 0 - don't panic, 1 - panic if already obsolete, 2 - panic if deprecated */
+static void
+gone_panic(int major, int running, const char *msg)
+{
+
+	switch (obsolete_panic)
+	{
+	case 0:
+		return;
+	case 1:
+		if (running < major)
+			return;
+		/* FALLTHROUGH */
+	default:
+		panic("%s", msg);
+	}
+}
+
+void
+_gone_in(int major, const char *msg)
+{
+	int m = __FreeBSD_version / 100000;
+
+	gone_panic(major, m, msg);
+	if (m >= major)
+		printf("Obsolete code running to be removed soon: %s\n", msg);
+	else if (m + 1 == major)
+		printf("Deprecated code (to be removed in FreeBSD %d): %s\n",
+		    major, msg);
+}
+
+void
+_gone_in_dev(device_t dev, int major, const char *msg)
+{
+	int m = __FreeBSD_version / 100000;
+
+	gone_panic(major, m, msg);
+	if (m >= major)
+		device_printf(dev,
+		    "Obsolete code running to be removed soon: %s\n", msg);
+	else if (m + 1 == major)
+		device_printf(dev,
+		    "Deprecated code (to be removed in FreeBSD %d): %s\n",
+		    major, msg);
+}
+
 #ifdef DDB
 DB_SHOW_COMMAND(device, db_show_device)
 {
Index: sys/sys/systm.h
===================================================================
--- sys/sys/systm.h
+++ sys/sys/systm.h
@@ -464,6 +464,22 @@
 
 void counted_warning(unsigned *counter, const char *msg);
 
+/*
+ * Obsolete management API.
+ */
+struct device;
+void _gone_in(int major, const char *msg);
+void _gone_in_dev(struct device *dev, int major, const char *msg);
+#ifdef NO_OBSOLETE_CODE
+#define __gone_ok(m, msg)					 \
+	_Static_assert(m < (__FreeBSD_version / 100000),	 \
+	    "Obsolete code" msg);
+#else
+#define	__gone_ok(m, msg)
+#endif
+#define gone_in(major, msg)		__gone_ok(major, msg) _gone_in(major, msg)
+#define gone_in_dev(dev, major, msg)	__gone_ok(major, msg) _gone_in_dev(dev, major, msg)
+
 __NULLABILITY_PRAGMA_POP
 
 #endif /* !_SYS_SYSTM_H_ */