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
  50struct notifier_block;
  51
  52typedef int (*notifier_fn_t)(struct notifier_block *nb,
  53                        unsigned long action, void *data);
  54
  55struct notifier_block {
  56        notifier_fn_t notifier_call;
  57        struct notifier_block __rcu *next;
  58        int priority;
  59};
  60
  61struct atomic_notifier_head {
  62        spinlock_t lock;
  63        struct notifier_block __rcu *head;
  64};
  65
  66struct blocking_notifier_head {
  67        struct rw_semaphore rwsem;
  68        struct notifier_block __rcu *head;
  69};
  70
  71struct raw_notifier_head {
  72        struct notifier_block __rcu *head;
  73};
  74
  75struct 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 */
  94extern 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
 120extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
 121                struct notifier_block *nb);
 122extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 123                struct notifier_block *nb);
 124extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 125                struct notifier_block *nb);
 126extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 127                struct notifier_block *nb);
 128
 129extern int blocking_notifier_chain_cond_register(
 130                struct blocking_notifier_head *nh,
 131                struct notifier_block *nb);
 132
 133extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 134                struct notifier_block *nb);
 135extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
 136                struct notifier_block *nb);
 137extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
 138                struct notifier_block *nb);
 139extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
 140                struct notifier_block *nb);
 141
 142extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 143                unsigned long val, void *v);
 144extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
 145        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 146extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 147                unsigned long val, void *v);
 148extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 149        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 150extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
 151                unsigned long val, void *v);
 152extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
 153        unsigned long val, void *v, int nr_to_call, int *nr_calls);
 154extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
 155                unsigned long val, void *v);
 156extern 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). */
 170static 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. */
 179static 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
 214extern struct blocking_notifier_head reboot_notifier_list;
 215
 216#endif /* __KERNEL__ */
 217#endif /* _LINUX_NOTIFIER_H */
 218