include/linux/notifier.h

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