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