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_struct srcu;
77 struct notifier_block __rcu *head;
78};
79
80#define ATOMIC_INIT_NOTIFIER_HEAD(name) do { \
81 spin_lock_init(&(name)->lock); \
82 (name)->head = NULL; \
83 } while (0)
84#define BLOCKING_INIT_NOTIFIER_HEAD(name) do { \
85 init_rwsem(&(name)->rwsem); \
86 (name)->head = NULL; \
87 } while (0)
88#define RAW_INIT_NOTIFIER_HEAD(name) do { \
89 (name)->head = NULL; \
90 } while (0)
91
92/* srcu_notifier_heads must be cleaned up dynamically */
93extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
94#define srcu_cleanup_notifier_head(name) \
95 cleanup_srcu_struct(&(name)->srcu);
96
97#define ATOMIC_NOTIFIER_INIT(name) { \
98 .lock = __SPIN_LOCK_UNLOCKED(name.lock), \
99 .head = NULL }
100#define BLOCKING_NOTIFIER_INIT(name) { \
101 .rwsem = __RWSEM_INITIALIZER((name).rwsem), \
102 .head = NULL }
103#define RAW_NOTIFIER_INIT(name) { \
104 .head = NULL }
105
106#define SRCU_NOTIFIER_INIT(name, pcpu) \
107 { \
108 .mutex = __MUTEX_INITIALIZER(name.mutex), \
109 .head = NULL, \
110 .srcu = __SRCU_STRUCT_INIT(name.srcu, pcpu), \
111 }
112
113#define ATOMIC_NOTIFIER_HEAD(name) \
114 struct atomic_notifier_head name = \
115 ATOMIC_NOTIFIER_INIT(name)
116#define BLOCKING_NOTIFIER_HEAD(name) \
117 struct blocking_notifier_head name = \
118 BLOCKING_NOTIFIER_INIT(name)
119#define RAW_NOTIFIER_HEAD(name) \
120 struct raw_notifier_head name = \
121 RAW_NOTIFIER_INIT(name)
122
123#ifdef CONFIG_TREE_SRCU
124#define _SRCU_NOTIFIER_HEAD(name, mod) \
125 static DEFINE_PER_CPU(struct srcu_data, name##_head_srcu_data); \
126 mod struct srcu_notifier_head name = \
127 SRCU_NOTIFIER_INIT(name, name##_head_srcu_data)
128
129#else
130#define _SRCU_NOTIFIER_HEAD(name, mod) \
131 mod struct srcu_notifier_head name = \
132 SRCU_NOTIFIER_INIT(name, name)
133
134#endif
135
136#define SRCU_NOTIFIER_HEAD(name) \
137 _SRCU_NOTIFIER_HEAD(name, /* not static */)
138
139#define SRCU_NOTIFIER_HEAD_STATIC(name) \
140 _SRCU_NOTIFIER_HEAD(name, static)
141
142#ifdef __KERNEL__
143
144extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
145 struct notifier_block *nb);
146extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
147 struct notifier_block *nb);
148extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
149 struct notifier_block *nb);
150extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
151 struct notifier_block *nb);
152
153extern int atomic_notifier_chain_register_unique_prio(
154 struct atomic_notifier_head *nh, struct notifier_block *nb);
155extern int blocking_notifier_chain_register_unique_prio(
156 struct blocking_notifier_head *nh, struct notifier_block *nb);
157
158extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
159 struct notifier_block *nb);
160extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
161 struct notifier_block *nb);
162extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
163 struct notifier_block *nb);
164extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
165 struct notifier_block *nb);
166
167extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
168 unsigned long val, void *v);
169extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
170 unsigned long val, void *v);
171extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
172 unsigned long val, void *v);
173extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
174 unsigned long val, void *v);
175
176extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
177 unsigned long val_up, unsigned long val_down, void *v);
178extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
179 unsigned long val_up, unsigned long val_down, void *v);
180
181extern bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh);
182
183#define NOTIFY_DONE 0x0000 /* Don't care */
184#define NOTIFY_OK 0x0001 /* Suits me */
185#define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
186#define NOTIFY_BAD (NOTIFY_STOP_MASK|0x0002)
187 /* Bad/Veto action */
188/*
189 * Clean way to return from the notifier and stop further calls.
190 */
191#define NOTIFY_STOP (NOTIFY_OK|NOTIFY_STOP_MASK)
192
193/* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
194static inline int notifier_from_errno(int err)
195{
196 if (err)
197 return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
198
199 return NOTIFY_OK;
200}
201
202/* Restore (negative) errno value from notify return value. */
203static inline int notifier_to_errno(int ret)
204{
205 ret &= ~NOTIFY_STOP_MASK;
206 return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
207}
208
209/*
210 * Declared notifiers so far. I can imagine quite a few more chains
211 * over time (eg laptop power reset chains, reboot chain (to clean
212 * device units up), device [un]mount chain, module load/unload chain,
213 * low memory chain, screenblank chain (for plug in modular screenblankers)
214 * VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
215 */
216
217/* CPU notfiers are defined in include/linux/cpu.h. */
218
219/* netdevice notifiers are defined in include/linux/netdevice.h */
220
221/* reboot notifiers are defined in include/linux/reboot.h. */
222
223/* Hibernation and suspend events are defined in include/linux/suspend.h. */
224
225/* Virtual Terminal events are defined in include/linux/vt.h. */
226
227#define NETLINK_URELEASE 0x0001 /* Unicast netlink socket released */
228
229/* Console keyboard events.
230 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
231 * KBD_KEYSYM. */
232#define KBD_KEYCODE 0x0001 /* Keyboard keycode, called before any other */
233#define KBD_UNBOUND_KEYCODE 0x0002 /* Keyboard keycode which is not bound to any other */
234#define KBD_UNICODE 0x0003 /* Keyboard unicode */
235#define KBD_KEYSYM 0x0004 /* Keyboard keysym */
236#define KBD_POST_KEYSYM 0x0005 /* Called after keyboard keysym interpretation */
237
238extern struct blocking_notifier_head reboot_notifier_list;
239
240#endif /* __KERNEL__ */
241#endif /* _LINUX_NOTIFIER_H */
242

source code of linux/include/linux/notifier.h