From 7faed6e3e94d7ec03443f27426bebbd5face1957 Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Mon, 29 Jan 2018 00:14:39 +0000
Subject: [PATCH] Create deprecation management functions.

gone_in(majar, msg);	If we're running in FreeBSD major, tell
			the user this code may be deleted soon.
			If we're running in FreeBSD major - 1,
			the the user is deprecated and will
			be gone in major.
			Otherwise say nothing.

gone_in_dev(dev, major, msg) Just like gone_in, except use device_printf.

New tunable / sysctl debug.oboslete_panic: 0 - don't panic,
	1 - panic in major or newer , 2 - panic in major - 1 or newer
	default: 0

if NO_OBSOLETE_CODE is defined, then both of these turn into compile
time errors when building for major. Add options NO_OBSOLETE_CODE to
kernel build system.

This lets us tag code that's going away so users know it will be gone,
as well as automatically manage things.

Differential Review: https://reviews.freebsd.org/D13818
---
 sys/conf/options    |  1 +
 sys/kern/subr_bus.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
 sys/sys/systm.h     | 16 +++++++++++++++
 3 files changed, 67 insertions(+)

diff --git a/sys/conf/options b/sys/conf/options
index 83505ef3982..b784079e231 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -177,6 +177,7 @@ NO_ADAPTIVE_MUTEXES	opt_adaptive_mutexes.h
 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
diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index 0151cd5e863..beb5ddfae44 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -5605,6 +5605,56 @@ devctl2_init(void)
 	    UID_ROOT, GID_WHEEL, 0600, "devctl2");
 }
 
+/*
+ * APIs to manage deprecation and obsolescence.
+ */
+static int obsolete_panic = 0;
+SYSCTL_INT(_debug, OID_AUTO, obsolete_panic, CTLFLAG_RWTUN, &obsolete_panic, 0,
+    "Bus debug level");
+/* 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)
+{
+
+	gone_panic(major, P_OSREL_MAJOR(__FreeBSD_version), msg);
+	if (P_OSREL_MAJOR(__FreeBSD_version) >= major)
+		printf("Obsolete code will removed soon: %s\n", msg);
+	else if (P_OSREL_MAJOR(__FreeBSD_version) + 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)
+{
+
+	gone_panic(major, P_OSREL_MAJOR(__FreeBSD_version), msg);
+	if (P_OSREL_MAJOR(__FreeBSD_version) >= major)
+		device_printf(dev,
+		    "Obsolete code will removed soon: %s\n", msg);
+	else if (P_OSREL_MAJOR(__FreeBSD_version) + 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)
 {
diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index a732cfc304c..051b80d84fd 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -464,6 +464,22 @@ void	intr_prof_stack_use(struct thread *td, struct trapframe *frame);
 
 void counted_warning(unsigned *counter, const char *msg);
 
+/*
+ * APIs to manage deprecation and obsolescence.
+ */
+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 < P_OSREL_MAJOR(__FreeBSD_version)),	 \
+	    "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_ */