LXR linux/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
  50typedef int (*notifier_fn_t)(struct notifier_block *nb,
  51                        unsigned long action, void *data);
  52
  53struct notifier_block {
  54        notifier_fn_t notifier_call;
  55        struct notifier_block __rcu *next;
  56        int priority;
  57};
  58
  59struct atomic_notifier_head {
  60        spinlock_t lock;
  61        struct notifier_block __rcu *head;
  62};
  63
  64struct blocking_notifier_head {
  65        struct rw_semaphore rwsem;
  66        struct notifier_block __rcu *head;
  67};
  68
  69struct raw_notifier_head {
  70        struct notifier_block __rcu *head;
  71};
  72
  73struct 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 */
  92extern 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
 118extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 119                struct notifier_block *nb);
 120extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 121                struct notifier_block *nb);
 122extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 123                struct notifier_block *nb);
 124extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 125                struct notifier_block *nb);
 126
 127extern int blocking_notifier_chain_cond_register(
 128                struct blocking_notifier_head *nh,
 129                struct notifier_block *nb);
 130
 131extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 132                struct notifier_block *nb);
 133extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 134                struct notifier_block *nb);
 135extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 136                struct notifier_block *nb);
 137extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 138                struct notifier_block *nb);
 139
 140extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 141                unsigned long val, void *v);
 142extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 143        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 144extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 145                unsigned long val, void *v);
 146extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 147        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 148extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 149                unsigned long val, void *v);
 150extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 151        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 152extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 153                unsigned long val, void *v);
 154extern 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). */
 168static 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. */
 177static 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
 212extern struct blocking_notifier_head reboot_notifier_list;
 213
 214#endif /* __KERNEL__ */
 215#endif /* _LINUX_NOTIFIER_H */
 216