linux/include/linux/notifier.h
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   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
  50struct notifier_block {
  51        int (*notifier_call)(struct notifier_block *, unsigned long, void *);
  52        struct notifier_block __rcu *next;
  53        int priority;
  54};
  55
  56struct atomic_notifier_head {
  57        spinlock_t lock;
  58        struct notifier_block __rcu *head;
  59};
  60
  61struct blocking_notifier_head {
  62        struct rw_semaphore rwsem;
  63        struct notifier_block __rcu *head;
  64};
  65
  66struct raw_notifier_head {
  67        struct notifier_block __rcu *head;
  68};
  69
  70struct 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 */
  89extern 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
 115extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 116                struct notifier_block *nb);
 117extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 118                struct notifier_block *nb);
 119extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 120                struct notifier_block *nb);
 121extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 122                struct notifier_block *nb);
 123
 124extern int blocking_notifier_chain_cond_register(
 125                struct blocking_notifier_head *nh,
 126                struct notifier_block *nb);
 127
 128extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 129                struct notifier_block *nb);
 130extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 131                struct notifier_block *nb);
 132extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 133                struct notifier_block *nb);
 134extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 135                struct notifier_block *nb);
 136
 137extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 138                unsigned long val, void *v);
 139extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 140        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 141extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 142                unsigned long val, void *v);
 143extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 144        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 145extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 146                unsigned long val, void *v);
 147extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 148        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 149extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 150                unsigned long val, void *v);
 151extern 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). */
 165static 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. */
 174static 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
 209extern struct blocking_notifier_head reboot_notifier_list;
 210
 211#endif /* __KERNEL__ */
 212#endif /* _LINUX_NOTIFIER_H */
 213
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