字符设备驱动

#include "linux/device/class.h"
#include "linux/export.h"
#include "linux/uaccess.h"
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cdev.h>

#define CHRDEVBASE_NAME "chrdevbase" /* 设备名 */
#define CHRDEVBASE_NUM 1             /* 设备数目 */

static char write_buf[100];
static char read_buf[100];

static char *string_test = "kernel data this tyustli test";

typedef struct {
    dev_t dev_id;          /* 设备号 */
    struct cdev c_dev;     /* cdev */
    struct class *class;   /* 类 */
    struct device *device; /* 设备 */
    int major;             /* 主设备号 */
    int minor;             /* 次设备号 */
} new_chrdev_t;

new_chrdev_t new_chrdev;

static int chrdevbase_open(struct inode *inode, struct file *file)
{
    printk("k: chrdevbase open\r\n");

    return 0;
}

static ssize_t chrdevbase_read(struct file *file, char __user *buf,
                               size_t count, loff_t *ppos)
{
    unsigned long ret = 0;

    printk("k: chrdevbase read\r\n");
    memcpy(read_buf, string_test, strlen(string_test));

    ret = copy_to_user(buf, read_buf, count);
    if (ret == 0) {
        printk("k: read data success\r\n");
    } else {
        printk("k: read data failed ret = %ld\r\n", ret);
    }

    return ret;
}

static ssize_t chrdevbase_write(struct file *file, const char __user *buf,
                                size_t count, loff_t *ppos)
{
    unsigned long ret = 0;

    printk("k: chrdevbase write\r\n");

    ret = copy_from_user(write_buf, buf, count);
    if (ret == 0) {
        printk("k: write data success write data is: %s\r\n", write_buf);
    } else {
        printk("k: write data failed ret = %ld\r\n", ret);
    }

    return count;
}

static int chrdevbase_release(struct inode *inode, struct file *file)
{
    printk("k: chrdevbase release\r\n");

    return 0;
}

static struct file_operations chrdevbase_fops = {
    .owner = THIS_MODULE,
    .open = chrdevbase_open,
    .read = chrdevbase_read,
    .write = chrdevbase_write,
    .release = chrdevbase_release,
};

static int __init chrdevbase_init(void)
{
    int err = 0;

    err = alloc_chrdev_region(&new_chrdev.dev_id, 0, CHRDEVBASE_NUM,
                              CHRDEVBASE_NAME);
    if (err < 0) {
        printk("k: alloc chrdev region failed err = %d\r\n", err);
        return -1;
    }

    /* get major and minor */
    new_chrdev.major = MAJOR(new_chrdev.dev_id);
    new_chrdev.minor = MINOR(new_chrdev.dev_id);
    printk("k: newcheled major=%d,minor=%d\r\n", new_chrdev.major,
           new_chrdev.minor);

    new_chrdev.c_dev.owner = THIS_MODULE;
    cdev_init(&new_chrdev.c_dev, &chrdevbase_fops);
    err = cdev_add(&new_chrdev.c_dev, new_chrdev.dev_id, CHRDEVBASE_NUM);
    if (err < 0) {
        printk("k: cdev add failed err = %d\r\n", err);
        goto out;
    }

    new_chrdev.class = class_create(CHRDEVBASE_NAME);
    if (IS_ERR(new_chrdev.class)) {
        printk("k: class create failed\r\n");
        goto out_cdev;
    }

    new_chrdev.device = device_create(new_chrdev.class, NULL, new_chrdev.dev_id,
                                      NULL, CHRDEVBASE_NAME);
    if (IS_ERR(new_chrdev.device)) {
        printk("k: device create failed\r\n");
        goto out_class;
    }

    printk("k: base module init\r\n");

    return 0;

out_class:
    class_destroy(new_chrdev.class);
out_cdev:
    cdev_del(&new_chrdev.c_dev);
out:
    unregister_chrdev_region(new_chrdev.dev_id, CHRDEVBASE_NUM);

    return err;
}

static void __exit chrdevbase_exit(void)
{
    device_destroy(new_chrdev.class, new_chrdev.dev_id);
    class_destroy(new_chrdev.class);
    cdev_del(&new_chrdev.c_dev);
    unregister_chrdev_region(new_chrdev.dev_id, CHRDEVBASE_NUM);

    printk("k: base module exit!\r\n");
}

module_init(chrdevbase_init);
module_exit(chrdevbase_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("tyustli");
MODULE_INFO(intree, "Y"); /* loading out-of-tree module taints kernel */

字符设备 APP

#include "stdio.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"

static char usrdata[] = { "user data!" };

int main(int argc, char *argv[])
{
    int fd, retvalue;
    char *filename;
    char readbuf[100], writebuf[100];

    if (argc != 3) {
        printf("u: error Usage!\r\n");
        return -1;
    }

    filename = argv[1];

    /* 打开驱动文件 */
    fd = open(filename, O_RDWR);
    if (fd < 0) {
        printf("u: can't open file %s\r\n", filename);
        return -1;
    }

    /* 从驱动文件读取数据 */
    if (atoi(argv[2]) == 1) {
        retvalue = read(fd, readbuf, 50);
        if (retvalue < 0) {
            printf("u: read file %s failed!\r\n", filename);
        } else {
            /*  读取成功，打印出读取成功的数据 */
            printf("u: read data:%s\r\n", readbuf);
        }
    }

    /* 向设备驱动写数据 */
    if (atoi(argv[2]) == 2) {
        memcpy(writebuf, usrdata, sizeof(usrdata));
        retvalue = write(fd, writebuf, 50);
        if (retvalue < 0) {
            printf("u: write file %s failed!\r\n", filename);
        }
    }

    /* 关闭设备 */
    retvalue = close(fd);
    if (retvalue < 0) {
        printf("u: can't close file %s\r\n", filename);
        return -1;
    }

    return 0;
}

生成 dev 节点的原理

dev 目录下的节点不是由驱动本身生成的，是由文件系统中的工具 mdev 生成的；

当系统启动后，加载完内核再去加载文件系统，执行文件系统中的脚本，脚本会执行 mdev -s 命令(即执行 mdev程序)，该命令会去遍历/sys/class下的所有文件，寻找所有名为 dev的文件，dev文件保存了每个驱动的主设备号、次设备号，以及驱动名。

生成设备节点的依赖有两个

• /sys/class 有驱动的节点信息，即 dev 文件
• 执行 mdev -s创建 /dev 下的节点

ls /sys/class

这里文件是有的，这个时候执行

mdev -s

并查看 /dev/ 目录

ls /dev

可以看到设备节点文件自动创建了

配置内核自动创建设备节点

配置 linux 内核使之自动创建设备节点文件

在内核中 make menuconfig 使能 CONFIG_UEVENT_HELPER

模块使用

linux 自动创建设备节点之后，就不用手动创建了，可以直接查看 /dev 目录下已经生成了设备节点文件

ls /dev

模块安装

modprobe my_module

模块使用

lib/modules/6.5.7+/my_app /dev/chrdevbase 1