sleepy分析

#include
#include

#include   /* current and everything */
#include /* printk() */
#include      /* everything... */
#include   /* size_t */
#include

MODULE_LICENSE("Dual BSD/GPL");

static int sleepy_major = 0;

static DECLARE_WAIT_QUEUE_HEAD(wq);   /*定义等待队列*/
static int flag = 0;

ssize_t sleepy_read (struct file *filp, char __user *buf, size_t count, loff_t *pos)
{
    printk(KERN_DEBUG "process %i (%s) going to sleep\n",
            current->pid, current->comm);
    wait_event_interruptible(wq, flag != 0);   /*使进程在给定等待队列上睡眠,直到给定条件为真*/
    flag = 0;
    printk(KERN_DEBUG "awoken %i (%s)\n", current->pid, current->comm);
    return 0; /* EOF */
}

ssize_t sleepy_write (struct file *filp, const char __user *buf, size_t count,
        loff_t *pos)
{
    printk(KERN_DEBUG "process %i (%s) awakening the readers...\n",
            current->pid, current->comm);  /*current->pid进程ID 和 current->command当前进程的命令名*/
    flag = 1;
    wake_up_interruptible(&wq);  /* 唤醒在等待队列 wq 上睡眠的进程 */
    return count; /* succeed, to avoid retrial */
}


struct file_operations sleepy_fops = {
    .owner = THIS_MODULE,
    .read =  sleepy_read,
    .write = sleepy_write,
};


int sleepy_init(void)
{
    int result;

    /*
     * Register your major, and accept a dynamic number
     */
    result = register_chrdev(sleepy_major, "sleepy", &sleepy_fops);
    if (result < 0)
        return result;
    if (sleepy_major == 0)
        sleepy_major = result; /* dynamic */
    return 0;
}

void sleepy_cleanup(void)
{
    unregister_chrdev(sleepy_major, "sleepy");
}

module_init(sleepy_init);
module_exit(sleepy_cleanup);