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
49 struct notifier_block;
50
51 typedef int (*notifier_fn_t)(struct notifier_block *nb,
52 unsigned long action, void *data);
53
54 struct notifier_block {
55 notifier_fn_t notifier_call;
56 struct notifier_block __rcu *next;
57 int priority;
58 };
59
60 struct atomic_notifier_head {
61 spinlock_t lock;
62 struct notifier_block __rcu *head;
63 };
64
65 struct blocking_notifier_head {
66 struct rw_semaphore rwsem;
67 struct notifier_block __rcu *head;
68 };
69
70 struct raw_notifier_head {
71 struct notifier_block __rcu *head;
72 };
73
74 struct 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 */
93 extern 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
144 extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
145 struct notifier_block *nb);
146 extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
147 struct notifier_block *nb);
148 extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
149 struct notifier_block *nb);
150 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
151 struct notifier_block *nb);
152
153 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
154 struct notifier_block *nb);
155 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
156 struct notifier_block *nb);
157 extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
158 struct notifier_block *nb);
159 extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
160 struct notifier_block *nb);
161
162 extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
163 unsigned long val, void *v);
164 extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
165 unsigned long val, void *v);
166 extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
167 unsigned long val, void *v);
168 extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
169 unsigned long val, void *v);
170
171 extern int atomic_notifier_call_chain_robust(struct atomic_notifier_head *nh,
172 unsigned long val_up, unsigned long val_down, void *v);
173 extern int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
174 unsigned long val_up, unsigned long val_down, void *v);
175 extern int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
176 unsigned long val_up, unsigned long val_down, void *v);
177
178 #define NOTIFY_DONE 0x0000 /* Don't care */
179 #define NOTIFY_OK 0x0001 /* Suits me */
180 #define NOTIFY_STOP_MASK 0x8000 /* Don't call further */
181 #define NOTIFY_BAD (NOTIFY_STOP_MASK|0x0002)
182 /* Bad/Veto action */
183 /*
184 * Clean way to return from the notifier and stop further calls.
185 */
186 #define NOTIFY_STOP (NOTIFY_OK|NOTIFY_STOP_MASK)
187
188 /* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
notifier_from_errno(int err)189 static inline int notifier_from_errno(int err)
190 {
191 if (err)
192 return NOTIFY_STOP_MASK | (NOTIFY_OK - err);
193
194 return NOTIFY_OK;
195 }
196
197 /* Restore (negative) errno value from notify return value. */
notifier_to_errno(int ret)198 static inline int notifier_to_errno(int ret)
199 {
200 ret &= ~NOTIFY_STOP_MASK;
201 return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
202 }
203
204 /*
205 * Declared notifiers so far. I can imagine quite a few more chains
206 * over time (eg laptop power reset chains, reboot chain (to clean
207 * device units up), device [un]mount chain, module load/unload chain,
208 * low memory chain, screenblank chain (for plug in modular screenblankers)
209 * VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
210 */
211
212 /* CPU notfiers are defined in include/linux/cpu.h. */
213
214 /* netdevice notifiers are defined in include/linux/netdevice.h */
215
216 /* reboot notifiers are defined in include/linux/reboot.h. */
217
218 /* Hibernation and suspend events are defined in include/linux/suspend.h. */
219
220 /* Virtual Terminal events are defined in include/linux/vt.h. */
221
222 #define NETLINK_URELEASE 0x0001 /* Unicast netlink socket released */
223
224 /* Console keyboard events.
225 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
226 * KBD_KEYSYM. */
227 #define KBD_KEYCODE 0x0001 /* Keyboard keycode, called before any other */
228 #define KBD_UNBOUND_KEYCODE 0x0002 /* Keyboard keycode which is not bound to any other */
229 #define KBD_UNICODE 0x0003 /* Keyboard unicode */
230 #define KBD_KEYSYM 0x0004 /* Keyboard keysym */
231 #define KBD_POST_KEYSYM 0x0005 /* Called after keyboard keysym interpretation */
232
233 extern struct blocking_notifier_head reboot_notifier_list;
234
235 #endif /* __KERNEL__ */
236 #endif /* _LINUX_NOTIFIER_H */
237