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. Also, SRCU notifier
47 * chains are slightly more difficult to use because they require special
48 * runtime initialization.
49 */
50
51 struct notifier_block;
52
53 typedef int (*notifier_fn_t)(struct notifier_block *nb,
54 unsigned long action, void *data);
55
56 struct notifier_block {
57 notifier_fn_t notifier_call;
58 struct notifier_block __rcu *next;
59 int priority;
60 };
61
62 struct atomic_notifier_head {
63 spinlock_t lock;
64 struct notifier_block __rcu *head;
65 };
66
67 struct blocking_notifier_head {
68 struct rw_semaphore rwsem;
69 struct notifier_block __rcu *head;
70 };
71
72 struct raw_notifier_head {
73 struct notifier_block __rcu *head;
74 };
75
76 struct srcu_notifier_head {
77 struct mutex mutex;
78 struct srcu_struct srcu;
79 struct notifier_block __rcu *head;
80 };
81
82 #define ATOMIC_INIT_NOTIFIER_HEAD(name) do { \
83 spin_lock_init(&(name)->lock); \
84 (name)->head = NULL; \
85 } while (0)
86 #define BLOCKING_INIT_NOTIFIER_HEAD(name) do { \
87 init_rwsem(&(name)->rwsem); \
88 (name)->head = NULL; \
89 } while (0)
90 #define RAW_INIT_NOTIFIER_HEAD(name) do { \
91 (name)->head = NULL; \
92 } while (0)
93
94 /* srcu_notifier_heads must be initialized and cleaned up dynamically */
95 extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
96 #define srcu_cleanup_notifier_head(name) \
97 cleanup_srcu_struct(&(name)->srcu);
98
99 #define ATOMIC_NOTIFIER_INIT(name) { \
100 .lock = __SPIN_LOCK_UNLOCKED(name.lock), \
101 .head = NULL }
102 #define BLOCKING_NOTIFIER_INIT(name) { \
103 .rwsem = __RWSEM_INITIALIZER((name).rwsem), \
104 .head = NULL }
105 #define RAW_NOTIFIER_INIT(name) { \
106 .head = NULL }
107 /* srcu_notifier_heads cannot be initialized statically */
108
109 #define ATOMIC_NOTIFIER_HEAD(name) \
110 struct atomic_notifier_head name = \
111 ATOMIC_NOTIFIER_INIT(name)
112 #define BLOCKING_NOTIFIER_HEAD(name) \
113 struct blocking_notifier_head name = \
114 BLOCKING_NOTIFIER_INIT(name)
115 #define RAW_NOTIFIER_HEAD(name) \
116 struct raw_notifier_head name = \
117 RAW_NOTIFIER_INIT(name)
118
119 #ifdef __KERNEL__
120
121 extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
122 struct notifier_block *nb);
123 extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
124 struct notifier_block *nb);
125 extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
126 struct notifier_block *nb);
127 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
128 struct notifier_block *nb);
129
130 extern int blocking_notifier_chain_cond_register(
131 struct blocking_notifier_head *nh,
132 struct notifier_block *nb);
133
134 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
135 struct notifier_block *nb);
136 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
137 struct notifier_block *nb);
138 extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
139 struct notifier_block *nb);
140 extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
141 struct notifier_block *nb);
142
143 extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
144 unsigned long val, void *v);
145 extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
146 unsigned long val, void *v, int nr_to_call, int *nr_calls);
147 extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
148 unsigned long val, void *v);
149 extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
150 unsigned long val, void *v, int nr_to_call, int *nr_calls);
151 extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
152 unsigned long val, void *v);
153 extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
154 unsigned long val, void *v, int nr_to_call, int *nr_calls);
155 extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
156 unsigned long val, void *v);
157 extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
158 unsigned long val, void *v, int nr_to_call, int *nr_calls);
159
160 #define NOTIFY_DONE 0x0000 /* Don't care */
161 #define NOTIFY_OK 0x0001 /* Suits me */
162 #define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
163 #define NOTIFY_BAD (NOTIFY_STOP_MASK|0x0002)
164 /* Bad/Veto action */
165 /*
166 * Clean way to return from the notifier and stop further calls.
167 */
168 #define NOTIFY_STOP (NOTIFY_OK|NOTIFY_STOP_MASK)
169
170 /* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
notifier_from_errno(int err)171 static inline int notifier_from_errno(int err)
172 {
173 if (err)
174 return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
175
176 return NOTIFY_OK;
177 }
178
179 /* Restore (negative) errno value from notify return value. */
notifier_to_errno(int ret)180 static inline int notifier_to_errno(int ret)
181 {
182 ret &= ~NOTIFY_STOP_MASK;
183 return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
184 }
185
186 /*
187 * Declared notifiers so far. I can imagine quite a few more chains
188 * over time (eg laptop power reset chains, reboot chain (to clean
189 * device units up), device [un]mount chain, module load/unload chain,
190 * low memory chain, screenblank chain (for plug in modular screenblankers)
191 * VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
192 */
193
194 /* CPU notfiers are defined in include/linux/cpu.h. */
195
196 /* netdevice notifiers are defined in include/linux/netdevice.h */
197
198 /* reboot notifiers are defined in include/linux/reboot.h. */
199
200 /* Hibernation and suspend events are defined in include/linux/suspend.h. */
201
202 /* Virtual Terminal events are defined in include/linux/vt.h. */
203
204 #define NETLINK_URELEASE 0x0001 /* Unicast netlink socket released */
205
206 /* Console keyboard events.
207 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
208 * KBD_KEYSYM. */
209 #define KBD_KEYCODE 0x0001 /* Keyboard keycode, called before any other */
210 #define KBD_UNBOUND_KEYCODE 0x0002 /* Keyboard keycode which is not bound to any other */
211 #define KBD_UNICODE 0x0003 /* Keyboard unicode */
212 #define KBD_KEYSYM 0x0004 /* Keyboard keysym */
213 #define KBD_POST_KEYSYM 0x0005 /* Called after keyboard keysym interpretation */
214
215 extern struct blocking_notifier_head reboot_notifier_list;
216
217 #endif /* __KERNEL__ */
218 #endif /* _LINUX_NOTIFIER_H */
219