notifier.h

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/*
 *  Routines to manage notifier chains for passing status changes to any
 *  interested routines. We need this instead of hard coded call lists so
 *  that modules can poke their nose into the innards. The network devices
 *  needed them so here they are for the rest of you.
 *
 *              Alan Cox <[email protected]>
 */
 
#ifndef _LINUX_NOTIFIER_H
#define _LINUX_NOTIFIER_H
#include <linux/errno.h>
#include <linux/mutex.h>
#include <linux/rwsem.h>
#include <linux/srcu.h>

/*
 * Notifier chains are of four types:
 *
 *  Atomic notifier chains: Chain callbacks run in interrupt/atomic
 *      context. Callouts are not allowed to block.
 *  Blocking notifier chains: Chain callbacks run in process context.
 *      Callouts are allowed to block.
 *  Raw notifier chains: There are no restrictions on callbacks,
 *      registration, or unregistration.  All locking and protection
 *      must be provided by the caller.
 *  SRCU notifier chains: A variant of blocking notifier chains, with
 *      the same restrictions.
 *
 * atomic_notifier_chain_register() may be called from an atomic context,
 * but blocking_notifier_chain_register() and srcu_notifier_chain_register()
 * must be called from a process context.  Ditto for the corresponding
 * _unregister() routines.
 *
 * atomic_notifier_chain_unregister(), blocking_notifier_chain_unregister(),
 * and srcu_notifier_chain_unregister() _must not_ be called from within
 * the call chain.
 *
 * SRCU notifier chains are an alternative form of blocking notifier chains.
 * They use SRCU (Sleepable Read-Copy Update) instead of rw-semaphores for
 * protection of the chain links.  This means there is _very_ low overhead
 * in srcu_notifier_call_chain(): no cache bounces and no memory barriers.
 * As compensation, srcu_notifier_chain_unregister() is rather expensive.
 * SRCU notifier chains should be used when the chain will be called very
 * often but notifier_blocks will seldom be removed.  Also, SRCU notifier
 * chains are slightly more difficult to use because they require special
 * runtime initialization.
 */

struct notifier_block {
    int (*notifier_call)(struct notifier_block *, unsigned long, void *);
    struct notifier_block __rcu *next;
    int priority;
};

struct atomic_notifier_head {
    spinlock_t lock;
    struct notifier_block __rcu *head;
};

struct blocking_notifier_head {
    struct rw_semaphore rwsem;
    struct notifier_block __rcu *head;
};

struct raw_notifier_head {
    struct notifier_block __rcu *head;
};

struct srcu_notifier_head {
    struct mutex mutex;
    struct srcu_struct srcu;
    struct notifier_block __rcu *head;
};

#define ATOMIC_INIT_NOTIFIER_HEAD(name) do {    \
        spin_lock_init(&(name)->lock);  \
        (name)->head = NULL;        \
    } while (0)
#define BLOCKING_INIT_NOTIFIER_HEAD(name) do {  \
        init_rwsem(&(name)->rwsem); \
        (name)->head = NULL;        \
    } while (0)
#define RAW_INIT_NOTIFIER_HEAD(name) do {   \
        (name)->head = NULL;        \
    } while (0)

/* srcu_notifier_heads must be initialized and cleaned up dynamically */
extern void srcu_init_notifier_head(struct srcu_notifier_head *nh);
#define srcu_cleanup_notifier_head(name)    \
        cleanup_srcu_struct(&(name)->srcu);

#define ATOMIC_NOTIFIER_INIT(name) {                \
        .lock = __SPIN_LOCK_UNLOCKED(name.lock),    \
        .head = NULL }
#define BLOCKING_NOTIFIER_INIT(name) {              \
        .rwsem = __RWSEM_INITIALIZER((name).rwsem), \
        .head = NULL }
#define RAW_NOTIFIER_INIT(name) {               \
        .head = NULL }
/* srcu_notifier_heads cannot be initialized statically */

#define ATOMIC_NOTIFIER_HEAD(name)              \
    struct atomic_notifier_head name =          \
        ATOMIC_NOTIFIER_INIT(name)
#define BLOCKING_NOTIFIER_HEAD(name)                \
    struct blocking_notifier_head name =            \
        BLOCKING_NOTIFIER_INIT(name)
#define RAW_NOTIFIER_HEAD(name)                 \
    struct raw_notifier_head name =             \
        RAW_NOTIFIER_INIT(name)

#ifdef __KERNEL__

extern int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
        struct notifier_block *nb);
extern int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
        struct notifier_block *nb);
extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
        struct notifier_block *nb);
extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
        struct notifier_block *nb);

extern int blocking_notifier_chain_cond_register(
        struct blocking_notifier_head *nh,
        struct notifier_block *nb);

extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
        struct notifier_block *nb);
extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
        struct notifier_block *nb);
extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
        struct notifier_block *nb);
extern int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
        struct notifier_block *nb);

extern int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
        unsigned long val, void *v);
extern int __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
    unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
        unsigned long val, void *v);
extern int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
    unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int raw_notifier_call_chain(struct raw_notifier_head *nh,
        unsigned long val, void *v);
extern int __raw_notifier_call_chain(struct raw_notifier_head *nh,
    unsigned long val, void *v, int nr_to_call, int *nr_calls);
extern int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
        unsigned long val, void *v);
extern int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
    unsigned long val, void *v, int nr_to_call, int *nr_calls);

#define NOTIFY_DONE     0x0000      /* Don't care */
#define NOTIFY_OK       0x0001      /* Suits me */
#define NOTIFY_STOP_MASK    0x8000      /* Don't call further */
#define NOTIFY_BAD      (NOTIFY_STOP_MASK|0x0002)
                        /* Bad/Veto action */
/*
 * Clean way to return from the notifier and stop further calls.
 */
#define NOTIFY_STOP     (NOTIFY_OK|NOTIFY_STOP_MASK)

/* Encapsulate (negative) errno value (in particular, NOTIFY_BAD <=> EPERM). */
static inline int notifier_from_errno(int err)
{
    if (err)
        return NOTIFY_STOP_MASK | (NOTIFY_OK - err);

    return NOTIFY_OK;
}

/* Restore (negative) errno value from notify return value. */
static inline int notifier_to_errno(int ret)
{
    ret &= ~NOTIFY_STOP_MASK;
    return ret > NOTIFY_OK ? NOTIFY_OK - ret : 0;
}

/*
 *  Declared notifiers so far. I can imagine quite a few more chains
 *  over time (eg laptop power reset chains, reboot chain (to clean 
 *  device units up), device [un]mount chain, module load/unload chain,
 *  low memory chain, screenblank chain (for plug in modular screenblankers) 
 *  VC switch chains (for loadable kernel svgalib VC switch helpers) etc...
 */
 
/* CPU notfiers are defined in include/linux/cpu.h. */

/* netdevice notifiers are defined in include/linux/netdevice.h */

/* reboot notifiers are defined in include/linux/reboot.h. */

/* Hibernation and suspend events are defined in include/linux/suspend.h. */

/* Virtual Terminal events are defined in include/linux/vt.h. */

#define NETLINK_URELEASE    0x0001  /* Unicast netlink socket released */

/* Console keyboard events.
 * Note: KBD_KEYCODE is always sent before KBD_UNBOUND_KEYCODE, KBD_UNICODE and
 * KBD_KEYSYM. */
#define KBD_KEYCODE     0x0001 /* Keyboard keycode, called before any other */
#define KBD_UNBOUND_KEYCODE 0x0002 /* Keyboard keycode which is not bound to any other */
#define KBD_UNICODE     0x0003 /* Keyboard unicode */
#define KBD_KEYSYM      0x0004 /* Keyboard keysym */
#define KBD_POST_KEYSYM     0x0005 /* Called after keyboard keysym interpretation */

extern struct blocking_notifier_head reboot_notifier_list;

#endif /* __KERNEL__ */
#endif /* _LINUX_NOTIFIER_H */