簡單字符驅動程序

原創

2020-02-21 19:05

mycdev.c:

#include<linux/init.h>

#include<linux/module.h>
#include<linux/types.h>
#include<linux/fs.h>
#include<linux/mm.h>
#include<linux/sched.h>
#include<linux/cdev.h>
#include<linux/kernel.h>
#include<asm/io.h>
#include<asm/uaccess.h>

MODULE_LICENSE("GPL");

#define MYCDEV_MAJOR 231     //cat /proc/devices查看系統中未使用的字符設備主設備號
#define MYCDEV_SIZE 1024

static int mycdev_open(struct inode *inode, struct file *fp)
{
    return 0;
}

static int mycdev_release(struct inode *inode, struct file *fp)
{
    return 0;
}

static ssize_t mycdev_read(struct file *fp, char __user *buf, size_t size, loff_t *pos)
{
    unsigned long p = *pos;
    unsigned int count = size;
    char kernel_buf[MYCDEV_SIZE] = "This is mycdev!";

    if(p >= MYCDEV_SIZE)
        return -1;
    if(count > MYCDEV_SIZE)
        count = MYCDEV_SIZE - p;
    if (copy_to_user(buf, kernel_buf, count) != 0) {
        printk("read error!\n");

        return -1;
    }
    printk("reader: %d bytes was read...\n",count);
    return count;
}

static ssize_t mycdev_write(struct file *fp, const char __user *buf, size_t size, loff_t *pos)
{
    return size;
}

static const struct file_operations mycdev_fops =
{
    .owner = THIS_MODULE,
    .read = mycdev_read,
    .write = mycdev_write,
    .open = mycdev_open,
    .release = mycdev_release,
};

static int __init mycdev_init(void)
{
    int ret;

    printk("mycdev module is staring..\n");

    ret =register_chrdev(MYCDEV_MAJOR, "my_cdev", &mycdev_fops);
    if (ret < 0) {
        printk("register failed..\n");
        return 0;
    } else {
        printk("register sucess..\n");
    }

    return 0;
}

static void __exit mycdev_exit(void)
{
    printk("mycdev module is leaving..\n");
    unregister_chrdev(MYCDEV_MAJOR, "my_cdev");
}

module_init(mycdev_init);

module_exit(mycdev_exit);

先編譯mycdev.c模塊，並把mycdev.ko插入內核。

然後創建設備文件結點sudo mknod /dev/mycdev c 231 0；（231的來源看代碼中的註釋）

修改設備文件權限：sudo chmod 777 /dev/mycdev.

編寫用戶態測試程序：test.c

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdlib.h>

int main()
{
    int testdev;
    int i, ret;
    char buf[10];

    testdev = open("/dev/mycdev", O_RDWR);

    if(testdev == -1) {
        printf("cannot open file.\n");
        exit(1);
    }

    if(ret = read(testdev, buf, 10) < 10) {
        printf("read error!\n");
        exit(1);
    }

    for (i=0; i<10; i++) {
        printf("%c", buf[i]);
    }
    printf("\n");
    close(testdev);

    return 0;
}