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