Linux内核通知链 使用和简析(2)

#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)

notifier_chain_register

无论是 ATOMIC BLOCKING RAW SRCU 的注册，都是对notifier_chain_register的封装， 以实现其特性
注册的过程就是讲新的链表元素按优先级添加到链表中去，大部分时候都是用的默认优先级

~/kernel/notifier.c

/*
 *  Notifier chain core routines.  The exported routines below
 *  are layered on top of these, with appropriate locking added.
 */

static int notifier_chain_register(struct notifier_block **nl,
        struct notifier_block *n)
{
    while ((*nl) != NULL) {
        if (n->priority > (*nl)->priority)
            break;
        nl = &((*nl)->next);
    }
    n->next = *nl;
    rcu_assign_pointer(*nl, n);
    return 0;
}12345678910111213141516171819

notifier_call_chain

所谓call chain 就是遍历链表，执行所有元素的notifier_call，并传递相关参数

/**
 * notifier_call_chain - Informs the registered notifiers about an event.
 *  @nl:        Pointer to head of the blocking notifier chain
 *  @val:      Value passed unmodified to notifier function
 *  @v:    Pointer passed unmodified to notifier function
 *  @nr_to_call:    Number of notifier functions to be called. Don't care
 *          value of this parameter is -1.
 *  @nr_calls:  Records the number of notifications sent. Don't care
 *          value of this field is NULL.
 *  @returns:  notifier_call_chain returns the value returned by the
 *          last notifier function called.
 */
static int notifier_call_chain(struct notifier_block **nl,
                  unsigned long val, void *v,
                  int nr_to_call, int *nr_calls)
{
    int ret = NOTIFY_DONE;
    struct notifier_block *nb, *next_nb;

nb = rcu_dereference_raw(*nl);

while (nb && nr_to_call) {
        next_nb = rcu_dereference_raw(nb->next);

#ifdef CONFIG_DEBUG_NOTIFIERS
        if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
            WARN(1, "Invalid notifier called!");
            nb = next_nb;
            continue;
        }
#endif
        ret = nb->notifier_call(nb, val, v);

if (nr_calls)
            (*nr_calls)++;

if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK)
            break;
        nb = next_nb;
        nr_to_call--;
    }
    return ret;
}

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