目录

博客说明

开发环境

1. Linux字符设备驱动的组成

1.1 字符设备驱动模块加载与卸载函数

1.2 字符设备驱动的file_operations 结构体中的成员函数

2. 字符设备驱动——设备号注册卸载

2.1 设备号注册

2.2 设备号注销

3. 字符设备驱动——文件操作

参考资料

示例代码

@(从Linux内核LED驱动来理解字符设备驱动开发流程)

博客说明

撰写日期

2018.12.08

完稿日期

2019.10.06

最近维护

暂无

本文作者

multimicro

联系方式

[email protected]

GitHub

https://github.com/wifialan

本文地址

https://blog.csdn.net/multimicro/article/details/84898135

开发环境

环境说明

详细信息

备注信息

操作系统

Ubunut 18.04.3 LTS

开发板

S3C2440(JZ2440-V3)

kernel版本

Linux-3.4.2

官网地址

busybox版本

busybox-1.22.1

官网地址

编译器

arm-Linux-gcc-4.4.3

下载地址

编译器路径

/opt/FriendlyARM/toolschain/4.4.3/bin

绝对路径

1. Linux字符设备驱动的组成

引自宋宝华《Linux设备驱动开发详解--基于最新的Linux 4.0内核》P138内容：

在Linux中，字符设备驱动由如下几个部分组成。

1. 字符设备驱动模块加载与卸载函数

2. 字符设备驱动的file_operations 结构体中的成员函数

这里先介绍一下字符设备的开发流程：字符设备驱动是通过设备号 与上位机程序连接。而上位机程序对驱动的控制则是通过文件操作，即read、write、ioctl等完成。

ps.(对于linux系统而言，一切皆文件，驱动加载成功后，会在/proc/devices里面添加驱动节点号信息)

因此一个字符设备驱动应包含1. 设备号的注册、卸载和2. 文件操作两个功能，注册的设备号用于提供接口，而文件操作用于对驱动的操作。

字符设备驱动的结构如下图所示：

对于cdev_init函数中，建立file_operations之间的连接的疑问，看一下cdev_init的实现

void cdev_init(struct cdev *cdev, const struct file_operations *fops)

{

memset(cdev, 0, sizeof *cdev);

INIT_LIST_HEAD(&cdev->list);

kobject_init(&cdev->kobj, &ktype_cdev_default);

cdev->ops = fops;

}

可以看出，最后的一个语句cdev->ops = fops;完成了在cdev中的file_operations的绑定

下面从程序语言角度感性的认识一下设备号的注册、卸载函数原型，和文件操作函数原型。

1.1 字符设备驱动模块加载与卸载函数

//加载函数

static int __init xxx_init(void)

{

... ...

}

//卸载函数

static int __exit xxx_exit(void)

{

... ...

}

1.2 字符设备驱动的file_operations 结构体中的成员函数

static const struct file_operations xxx_fileops = {

.owner = THIS_MODULE,

.write = xxx_write,

.read = xxx_read,

.open = xxx_open,

.unlocked_ioctl = xxx_ioctl,

... ...

};

static int xxx_open( struct inode *inodes, struct file *filp )

{

... ...

}

static long xxx_ioctl( struct file *file, unsigned int cmd, unsigned long arg )

{

... ...

}

static ssize_t xxx_write( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos )

{

... ...

}

static ssize_t xxx_read( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos )

{

... ...

}

2. 字符设备驱动——设备号注册卸载

以我写的字符设备驱动源代码为例，路径为Linux-3.4.2\drivers\char\s3c2440_leds.c，文章后附有完整的代码

设备号的注册由static int __init s3c2440_leds_init(void)完成

设备号的卸载由static int __init s3c2440_leds_exit(void)完成

首先分析设备号的注册，然后分析卸载

2.1 设备号注册

设备号分为主设备号和次设备号，若源代码中定义了主设备号(次设备号一般为0)，那么可以直接完成设备号的注册，其流程为

注册成功后，可通过cat /proc/devices命令查看设备号

2.2 设备号注销

相比设备号的注册，注销流程就十分简单：

3. 字符设备驱动——文件操作

当上位机程序通过调用open函数打开(链接上)相应的驱动程序后，open函数会返回一个==文件描述符==暂且记为fd，然后对该驱动的read、write、ioctl等操作都可以通过使用fd完成。简单的字符设备驱动程序大多采用ioctl函数控制驱动程序，而这个ioctl函数本身也不难，其实现为：

static long s3c2440_leds_ioctl( struct file *file, unsigned int cmd, unsigned long arg )

函数中

第一个参数：表示要操作的文件描述符

第二个参数：表示传递的命令字

第三个参数：表示传递的变量字

第二个参数和第三个参数的含义没有硬性规定，传递的参数符合对应的关键字限定类型即可

下面的给出示例参考

static long s3c2440_leds_ioctl( struct file *file, unsigned int cmd, unsigned long arg )

{

printk(DRV_NAME "\tRecv cmd: %u\n", cmd);

printk(DRV_NAME "\tRecv arg: %lu\n", arg);

//IO operations function.

if(arg > 4) {

return -EINVAL;

}

switch (cmd) {

case IOCTL_LED_ON: //#define IOCTL_LED_ON 1

s3c2410_gpio_setpin(S3C2410_GPF(arg+3), 0);//Set pin

printk("Open LED %lu ",arg);

return 0;

case IOCTL_LED_OFF: //#define IOCTL_LED_OFF 0

s3c2410_gpio_setpin(S3C2410_GPF(arg+3), 1);

printk("Close LED %lu ",arg);

return 0;

default:

return -EINVAL;

}

}

参考资料

1. 宋宝华《Linux设备驱动开发详解–基于最新的Linux 4.0内核》 第6章 字符设备驱动

示例代码

/*

* Driver for S3C2440 base board.

*

* Copyright (C) 2019 Alan NWPU

*

* This program is free software; you can redistribute it and/or modify

* it under the terms of the GNU General Public License as published by

* the Free Software Foundation; either version 2 of the License, or

* (at your option) any later version.

*

* This program is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU General Public License

* along with this program; if not, write to the Free Software

* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

* MULTIBEANS, NPU Youyi West Ave, Beilin District, Xi'an, China.

*/

#include /* Every Linux kernel module must include this head */

#include /* Every Linux kernel module must include this head */

#include /* printk() */

#include /* struct fops */

#include /* error codes */

#include /* cdev_alloc() */

#include /* request_mem_region() */

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#define DRV_NAME "s3c2440_leds"

#define DRV_AUTHOR "Alan Tian "

#define DRV_DESC "S3C2440 LED Pin Driver"

#define S3C2440_LED_SIZE 0x1000

#define S3C2440_LED_MAJOR 230

#define S3C2440_LED_MINOR 0

static int major = S3C2440_LED_MAJOR;

static int minor = S3C2440_LED_MINOR;

/* 应用程序执行ioctl(fd, cmd, arg)时的第2个参数 */

#define IOCTL_LED_ON 0

#define IOCTL_LED_OFF 1

static int s3c2440_leds_open( struct inode *inodes, struct file *filp );

static long s3c2440_leds_ioctl( struct file *file, unsigned int cmd, unsigned long arg );

static ssize_t s3c2440_leds_write( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos );

static ssize_t s3c2440_leds_read( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos );

struct s3c2440_leds_dev_t

{

struct cdev cdev;

unsigned char mem[S3C2440_LED_SIZE];

} *s3c2440_leds_dev;

//Step 2: Add file operations

static const struct file_operations s3c2440_leds_fileops = {

.owner = THIS_MODULE,

.write = s3c2440_leds_write,

.read = s3c2440_leds_read,

.open = s3c2440_leds_open,

.unlocked_ioctl = s3c2440_leds_ioctl,

};

static int s3c2440_leds_open( struct inode *inodes, struct file *filp )

{

//int ret;

filp->private_data = s3c2440_leds_dev;

printk(DRV_NAME"\tS3C2440 open function...\n");

return 0;

}

static long s3c2440_leds_ioctl( struct file *file, unsigned int cmd, unsigned long arg )

{

printk(DRV_NAME "\tRecv cmd: %u\n", cmd);

printk(DRV_NAME "\tRecv arg: %lu\n", arg);

//IO operations function.

if(arg > 4) {

return -EINVAL;

}

switch (cmd) {

case IOCTL_LED_ON:

s3c2410_gpio_setpin(S3C2410_GPF(arg+3), 0);//Set pin

printk("Open LED %lu ",arg);

return 0;

case IOCTL_LED_OFF:

s3c2410_gpio_setpin(S3C2410_GPF(arg+3), 1);

printk("Close LED %lu ",arg);

return 0;

default:

return -EINVAL;

}

}

static ssize_t s3c2440_leds_write( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos )

{

unsigned long p = *f_pos;

unsigned int count = size;

int ret = 0;

struct s3c2440_leds_dev_t *dev = filp->private_data;

if(p >= S3C2440_LED_SIZE)

return 0;

if(count > S3C2440_LED_SIZE - p)

count = S3C2440_LED_SIZE - p;

memset(dev->mem, 0, S3C2440_LED_SIZE);

if(copy_from_user(dev->mem + p, buffer, count)) {

ret = -EFAULT;

} else {

*f_pos += count;

ret = count;

printk(KERN_INFO "writter %u bytes(s) from %lu\n", count, p);

}

return ret;

}

static ssize_t s3c2440_leds_read( struct file *filp, const char __user *buffer, size_t size, loff_t *f_pos )

{

unsigned long p = *f_pos;

unsigned int count = size;

int ret = 0;

struct s3c2440_leds_dev_t *dev = filp->private_data;

if(p >= S3C2440_LED_SIZE)

return 0;

if(count > S3C2440_LED_SIZE - p)

count = S3C2440_LED_SIZE - p;

if(copy_to_user(buffer, dev->mem + p, count)) {

ret = -EFAULT;

} else {

*f_pos += count;

ret = count;

printk(KERN_INFO "read %u bytes(s) from %lu\n", count, p);

}

return ret;

}

static int __init s3c2440_leds_init(void)

{

int ret,err;

dev_t devid;

if(major) {

devid = MKDEV(major, 0);

ret = register_chrdev_region(devid, 1, DRV_NAME);

printk("Origin Creat node %d\n",major);

} else {

ret = alloc_chrdev_region(&devid, 0, 1, DRV_NAME);

major = MAJOR(devid);

printk("Arrage1 Creat node %d\n",major);

}

if(ret < 0) {

printk(DRV_NAME "\ts3c2440 new device failed\n");

//goto fail_malloc;

return ret;

}

s3c2440_leds_dev = kzalloc(sizeof(struct s3c2440_leds_dev_t), GFP_KERNEL);

if(!s3c2440_leds_dev) {

ret = -ENOMEM;

goto fail_malloc;

}

printk("success init leds\n");

cdev_init(&s3c2440_leds_dev->cdev, &s3c2440_leds_fileops);

err = cdev_add(&s3c2440_leds_dev->cdev, devid, 1);

if(err)

printk(KERN_NOTICE "Error %d adding s2c2440_leds %d",err, 1);

return 0;

fail_malloc:

unregister_chrdev_region(devid, 1);

return ret;

}

static void __exit s3c2440_leds_exit(void)

{

printk("Starting delet node %d\n",major);

cdev_del(&s3c2440_leds_dev->cdev);

kfree(s3c2440_leds_dev);

unregister_chrdev_region(MKDEV(major, minor), 1);

printk("Delete node %d\n",major);

}

module_init(s3c2440_leds_init);

module_exit(s3c2440_leds_exit);

MODULE_AUTHOR(DRV_AUTHOR);

MODULE_DESCRIPTION(DRV_DESC);

MODULE_LICENSE("GPL");