1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 *	Routines to manage notifier chains for passing status changes to any
4 *	interested routines. We need this instead of hard coded call lists so
5 *	that modules can poke their nose into the innards. The network devices
6 *	needed them so here they are for the rest of you.
7 *
8 *				Alan Cox <Alan.Cox@linux.org>
9 */
10
11#ifndef _LINUX_NOTIFIER_H
12#define _LINUX_NOTIFIER_H
13#include <linux/errno.h>
14#include <linux/mutex.h>
15#include <linux/rwsem.h>
16#include <linux/srcu.h>
17
18/*
19 * Notifier chains are of four types:
20 *
21 *	Atomic notifier chains: Chain callbacks run in interrupt/atomic
22 *		context. Callouts are not allowed to block.
23 *	Blocking notifier chains: Chain callbacks run in process context.
24 *		Callouts are allowed to block.
25 *	Raw notifier chains: There are no restrictions on callbacks,
26 *		registration, or unregistration.  All locking and protection
27 *		must be provided by the caller.
28 *	SRCU notifier chains: A variant of blocking notifier chains, with
29 *		the same restrictions.
30 *
31 * atomic_notifier_chain_register() may be called from an atomic context,
32 * but blocking_notifier_chain_register() and srcu_notifier_chain_register()
33 * must be called from a process context.  Ditto for the corresponding
34 * _unregister() routines.
35 *
36 * atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
37 * and srcu_notifier_chain_unregister() _must not_ be called from within
38 * the call chain.
39 *
40 * SRCU notifier chains are an alternative form of blocking notifier chains.
41 * They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
42 * protection of the chain links.  This means there is _very_ low overhead
43 * in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
44 * As compensation, srcu_notifier_chain_unregister() is rather expensive.
45 * SRCU notifier chains should be used when the chain will be called very
46 * often but notifier_blocks will seldom be removed.
47 */
48
49struct notifier_block;
50
51typedef	int (*notifier_fn_t)(struct notifier_block *nb,
52			unsigned long action, void *data);
53
54struct notifier_block {
55	notifier_fn_t notifier_call;
56	struct notifier_block __rcu *next;
57	int priority;
58};
59
60struct atomic_notifier_head {
61	spinlock_t lock;
62	struct notifier_block __rcu *head;
63};
64
65struct blocking_notifier_head {
66	struct rw_semaphore rwsem;
67	struct notifier_block __rcu *head;
68};
69
70struct raw_notifier_head {
71	struct notifier_block __rcu *head;
72};
73
74struct srcu_notifier_head {
75	struct mutex mutex;
76	struct srcu_usage srcuu;
77	struct srcu_struct srcu;
78	struct notifier_block __rcu *head;
79};
80
81#define ATOMIC_INIT_NOTIFIER_HEAD(name) do {	\
82		spin_lock_init(&(name)->lock);	\
83		(name)->head = NULL;		\
84	} while (0)
85#define BLOCKING_INIT_NOTIFIER_HEAD(name) do {	\
86		init_rwsem(&(name)->rwsem);	\
87		(name)->head = NULL;		\
88	} while (0)
89#define RAW_INIT_NOTIFIER_HEAD(name) do {	\
90		(name)->head = NULL;		\
91	} while (0)
92
93/* srcu_notifier_heads must be cleaned up dynamically */
94extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
95#define srcu_cleanup_notifier_head(name)	\
96		cleanup_srcu_struct(&(name)->srcu);
97
98#define ATOMIC_NOTIFIER_INIT(name) {				\
99		.lock = __SPIN_LOCK_UNLOCKED(name.lock),	\
100		.head = NULL }
101#define BLOCKING_NOTIFIER_INIT(name) {				\
102		.rwsem = __RWSEM_INITIALIZER((name).rwsem),	\
103		.head = NULL }
104#define RAW_NOTIFIER_INIT(name)	{				\
105		.head = NULL }
106
107#define SRCU_NOTIFIER_INIT(name, pcpu)				\
108	{							\
109		.mutex = __MUTEX_INITIALIZER(name.mutex),	\
110		.head = NULL,					\
111		.srcuu = __SRCU_USAGE_INIT(name.srcuu),		\
112		.srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \
113	}
114
115#define ATOMIC_NOTIFIER_HEAD(name)				\
116	struct atomic_notifier_head name =			\
117		ATOMIC_NOTIFIER_INIT(name)
118#define BLOCKING_NOTIFIER_HEAD(name)				\
119	struct blocking_notifier_head name =			\
120		BLOCKING_NOTIFIER_INIT(name)
121#define RAW_NOTIFIER_HEAD(name)					\
122	struct raw_notifier_head name =				\
123		RAW_NOTIFIER_INIT(name)
124
125#ifdef CONFIG_TREE_SRCU
126#define _SRCU_NOTIFIER_HEAD(name, mod)				\
127	static DEFINE_PER_CPU(struct srcu_data, name##_head_srcu_data); \
128	mod struct srcu_notifier_head name =			\
129			SRCU_NOTIFIER_INIT(name, name##_head_srcu_data)
130
131#else
132#define _SRCU_NOTIFIER_HEAD(name, mod)				\
133	mod struct srcu_notifier_head name =			\
134			SRCU_NOTIFIER_INIT(name, name)
135
136#endif
137
138#define SRCU_NOTIFIER_HEAD(name)				\
139	_SRCU_NOTIFIER_HEAD(name, /* not static */)
140
141#define SRCU_NOTIFIER_HEAD_STATIC(name)				\
142	_SRCU_NOTIFIER_HEAD(name, static)
143
144#ifdef __KERNEL__
145
146extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
147		struct notifier_block *nb);
148extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
149		struct notifier_block *nb);
150extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
151		struct notifier_block *nb);
152extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
153		struct notifier_block *nb);
154
155extern int atomic_notifier_chain_register_unique_prio(
156		struct atomic_notifier_head *nh, struct notifier_block *nb);
157extern int blocking_notifier_chain_register_unique_prio(
158		struct blocking_notifier_head *nh, struct notifier_block *nb);
159
160extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
161		struct notifier_block *nb);
162extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
163		struct notifier_block *nb);
164extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
165		struct notifier_block *nb);
166extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
167		struct notifier_block *nb);
168
169extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
170		unsigned long val, void *v);
171extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
172		unsigned long val, void *v);
173extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
174		unsigned long val, void *v);
175extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
176		unsigned long val, void *v);
177
178extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
179		unsigned long val_up, unsigned long val_down, void *v);
180extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
181		unsigned long val_up, unsigned long val_down, void *v);
182
183extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
184
185#define NOTIFY_DONE		0x0000		/* Don't care */
186#define NOTIFY_OK		0x0001		/* Suits me */
187#define NOTIFY_STOP_MASK	0x8000		/* Don't call further */
188#define NOTIFY_BAD		(NOTIFY_STOP_MASK|0x0002)
189						/* Bad/Veto action */
190/*
191 * Clean way to return from the notifier and stop further calls.
192 */
193#define NOTIFY_STOP		(NOTIFY_OK|NOTIFY_STOP_MASK)
194
195/* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
196static inline int notifier_from_errno(int err)
197{
198	if (err)
199		return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
200
201	return NOTIFY_OK;
202}
203
204/* Restore (negative) errno value from notify return value. */
205static inline int notifier_to_errno(int ret)
206{
207	ret &= ~NOTIFY_STOP_MASK;
208	return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
209}
210
211/*
212 *	Declared notifiers so far. I can imagine quite a few more chains
213 *	over time (eg laptop power reset chains, reboot chain (to clean
214 *	device units up), device [un]mount chain, module load/unload chain,
215 *	low memory chain, screenblank chain (for plug in modular screenblankers)
216 *	VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
217 */
218
219/* CPU notfiers are defined in include/linux/cpu.h. */
220
221/* netdevice notifiers are defined in include/linux/netdevice.h */
222
223/* reboot notifiers are defined in include/linux/reboot.h. */
224
225/* Hibernation and suspend events are defined in include/linux/suspend.h. */
226
227/* Virtual Terminal events are defined in include/linux/vt.h. */
228
229#define NETLINK_URELEASE	0x0001	/* Unicast netlink socket released */
230
231/* Console keyboard events.
232 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
233 * KBD_KEYSYM. */
234#define KBD_KEYCODE		0x0001 /* Keyboard keycode, called before any other */
235#define KBD_UNBOUND_KEYCODE	0x0002 /* Keyboard keycode which is not bound to any other */
236#define KBD_UNICODE		0x0003 /* Keyboard unicode */
237#define KBD_KEYSYM		0x0004 /* Keyboard keysym */
238#define KBD_POST_KEYSYM		0x0005 /* Called after keyboard keysym interpretation */
239
240extern struct blocking_notifier_head reboot_notifier_list;
241
242#endif /* __KERNEL__ */
243#endif /* _LINUX_NOTIFIER_H */
244