kill_fasync及fasync_helper

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我是靠谱客的博主清脆外套，最近开发中收集的这篇文章主要介绍kill_fasync及fasync_helper，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

kill_fasync及fasync_helper用于异步通知中

kill_fasync(&dev->async_queue, SIGIO, POLL_IN); //向app发可读信号，dev->async_queue可用来区分向谁发

那个进程调用这个fasync_helper就向谁发

int fasync_helper(int fd, struct file * filp, int on, struct fasync_struct **fapp)
{
    struct fasync_struct *fa, **fp;
    struct fasync_struct *new = NULL;
    int result = 0;

    if (on) {
        new = kmem_cache_alloc(fasync_cache, GFP_KERNEL);
        if (!new)
            return -ENOMEM;
    }
    write_lock_irq(&fasync_lock);
    for (fp = fapp; (fa = *fp) != NULL; fp = &fa->fa_next) {
        if (fa->fa_file == filp) {
            if(on) {
                fa->fa_fd = fd;   //区分向谁发
                kmem_cache_free(fasync_cache, new);
            } else {
                *fp = fa->fa_next;
                kmem_cache_free(fasync_cache, fa);
                result = 1;
            }
            goto out;
        }
    }

    if (on) {
        new->magic = FASYNC_MAGIC;
        new->fa_file = filp;
        new->fa_fd = fd;
        new->fa_next = *fapp;
        *fapp = new;
        result = 1;
    }
out:
    write_unlock_irq(&fasync_lock);
    return result;
}
别忘了realease时调用一把释放

所以用法为
task1
    signal(SIGIO, input_handler); //让input_handler()处理SIGIO信号
    fcntl(fd, F_SETOWN, getpid());
    oflags = fcntl(fd, F_GETFL);
    fcntl(fd, F_SETFL, oflags | FASYNC); //调用驱动的fasync_helper

task2
    kill_fasync发送信号调用signal安装的信号

   设备关闭时   kpp_fasync(-1, filp, 0);