如何在Linux内核读取功能中将字符串copy_to_user和使用offp [英] How to copy_to_user a string and use offp in a Linux Kernel read function

问题描述

已声明:

static char status[128] = "off\0";

并实现了read函数:

static ssize_t read_proc(struct file *filep, char __user *buf,
                    size_t len, loff_t *offp)
{
    ssize_t cnt = strlen(status), ret;

    ret = copy_to_user(buf, status, cnt);
    *offp += cnt;
    return cnt;
}

• 如何考虑offp?
• 当前它会在屏幕上连续显示status
• How do I take into account the offp?
• currently it prints endless the status to screen

推荐答案

在此感谢大家的意见，我提出了以下实现，我认为这是使用offp的正确方法:

Thanks the guys comments here I came up with the following implementation, which I believe is the right way to use offp:

static ssize_t read_proc(struct file *filep, char __user *buf,
                    size_t len, loff_t *offp)
{

    ssize_t cnt = strlen(status), ret;

    /* ret contains the amount of chare wasn't successfully written to `buf` */
    ret = copy_to_user(buf, status, cnt);
    *offp += cnt - ret;

    /* Making sure there are no left bytes of data to send user */
    if (*offp > cnt)
         return 0;
    else
         return cnt;
}

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