cat 函数无限次调用 read() [英] cat function calling read() infinite times

问题描述

我正在研究简单的字符设备驱动程序.我在模块中实现了读写功能，问题是当我尝试使用 cat/dev/devicefile 读取设备文件时，它进入无限循环，即重复读取相同的数据.有人可以建议我解决这个问题吗?下面是我的驱动程序代码.

I am working on simple character device driver. I have implemented read and write functions in the module, the problem is when I try to read the device file using cat /dev/devicefile it is going into infinite loop i.e. reading the same data repeatedly. Can someone suggest me any solution to this problem? Below is my driver code.

#include<linux/module.h>
#include<linux/fs.h>
#include<linux/string.h>
#include<asm/uaccess.h>
#include<linux/init.h>
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("character device driver");
MODULE_AUTHOR("Srinivas");

static char msg[100]={0};

static int t;

static int dev_open(struct inode *, struct file *);
static int dev_rls(struct inode *, struct file *);
static ssize_t dev_read(struct file *, char *,size_t, loff_t *);
static ssize_t dev_write(struct file *, const char *, size_t,loff_t *);

static struct file_operations fops =
{
    .read = dev_read,
    .open = dev_open,
    .write = dev_write,
    .release = dev_rls,
};
static int himodule( void )
{
    t = 0;
    t = register_chrdev(0, "chardevdriver", &fops);
    if (t < 0)
        printk(KERN_ALERT"device registration failed
");
    else
        printk(KERN_ALERT"device registered successfully
");

    printk(KERN_ALERT"major number is %d", t);
    return 0;
}
static void byemodule(void)
{
    unregister_chrdev(t, "chardevdriver");
    printk(KERN_ALERT"successfully unregistered
");
}

static int dev_open(struct inode *inod, struct file *fil)
{
    printk(KERN_ALERT"inside the dev open");
    return 0;
}
static ssize_t dev_read(struct file *filp, char *buff, size_t len, loff_t *off)
{
    short count = 0;
    while (msg[count] != 0) {
        put_user(msg[count], buff++);
        count++;
    }
    return count;
}

static ssize_t dev_write(struct file *filp, const char *buff, size_t len, loff_t *off)
{
    short count = 0;
    printk(KERN_ALERT"inside write
");

    memset(msg,0,100);

    printk(KERN_ALERT" size of len is %zd",len);

    while (len > 0) {
        msg[count] = buff[count];
        len--;
        count++;
    }
    return count;
}

static int dev_rls(struct inode *inod,struct file *fil)
{
    printk(KERN_ALERT"device closed
");
    return 0;
}
module_init(himodule);
module_exit(byemodule);

推荐答案

.read 函数也应该正确处理它的 len 和 off 参数.实现从内存缓冲文件读取的最简单方法是使用 simple_read_from_buffer 助手:

.read function should also correctly process its len and off arguments. The simplest way to implement reading from memory-buffered file is to use simple_read_from_buffer helper:

static ssize_t dev_read(struct file *filp, char *buff, size_t len, loff_t *off)
{
    return simple_read_from_buffer(buff, len, off, msg, 100);
}

您可以出于教育目的检查该助手的代码(在 fs/libfs.c 中定义).

You can inspect code of that helper (defined in fs/libfs.c) for educational purposes.

顺便说一句，对于您的 .write 方法，您可以使用 simple_write_to_buffer 助手.

BTW, for your .write method you could use simple_write_to_buffer helper.

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