cat命令在无限循环中运行cat / proc / jiffies

Question

我编写了一个简单的proc文件，以从内核获取秒数的滴答声，但是当我运行cat命令时，我得到秒数的滴答声，但是循环永远不会结束。 linux版本4.18.14

static ssize_t proc_read_jiffies(struct file *fp, char *buf, size_t len, loff_t *offset)
{

        static int finished = 0; 
        if (finished){
            finished = 0; 
            return (int)0;
        }
        finished=1;
        int lenr;
        //lenr = sprintf(buf, "jiffies = %ld \n",jiffies);
        time = ( jiffies - jiffies_start )/HZ;
        sprintf(buf,"time elapsed = %d \n",time);
        return (int)strlen(buf);
}

static struct file_operations jiffiesRead = 
{
    .owner = THIS_MODULE,
    .read = proc_read_jiffies,
};

static int init_procfs_example(void)
{

        jiffies_file = proc_create("jiffies", 
                                      0666, NULL,
                                      &jiffiesRead);
        jiffies_start = jiffies;

        /* everything OK */
        printk(KERN_INFO "%s %s initialised\n",MODULE_NAME, MODULE_VERS);
        return 0;


}