嵌入式Linux字符设备驱动开发流程——以LED为例

1.设备模块加载及卸载
2.静态申请设备号
3.动态申请设备号
4.注册字符类设备
5.生成字符设备节点
6.完善字符类设备驱动
7.根据完善后的模板编写相关设备驱动

前言

留空

头文件

#include <linux/fs.h>         //文件操作的结构体
      

文件的结构体

文件(路径)：未知

/*
* NOTE:
* all file operations except setlease can be called without
* the big kernel lock held in all filesystems.
*/
struct file_operations {
    struct module *owner;
    loff_t (*llseek) (struct file *, loff_t, int);
    ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
    ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
    ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
    ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
    int (*readdir) (struct file *, void *, filldir_t);
    unsigned int (*poll) (struct file *, struct poll_table_struct *);
/* remove by cym 20130408 support for MT660.ko */
#if 0
//#ifdef CONFIG_SMM6260_MODEM
#if 1// liang, Pixtree also need to use ioctl interface...
    int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
#endif
#endif
/* end remove */
    long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
    long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
    int (*mmap) (struct file *, struct vm_area_struct *);
    int (*open) (struct inode *, struct file *);
    int (*flush) (struct file *, fl_owner_t id);
    int (*release) (struct inode *, struct file *);
    int (*fsync) (struct file *, int datasync);
    int (*aio_fsync) (struct kiocb *, int datasync);
    int (*fasync) (int, struct file *, int);
    int (*lock) (struct file *, int, struct file_lock *);
    ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
    unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
    int (*check_flags)(int);
    int (*flock) (struct file *, int, struct file_lock *);
    ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
    ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
    int (*setlease)(struct file *, long, struct file_lock **);
    long (*fallocate)(struct file *file, int mode, loff_t offset,
              loff_t len);
/* add by cym 20130408 support for MT6260 and Pixtree */
#if defined(CONFIG_SMM6260_MODEM) || defined(CONFIG_USE_GPIO_AS_I2C)
    int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
#endif
/* end add */
};

文件的结构体的常用参数

struct file_operations {
    struct module *owner;
    ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
    ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
    int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
    long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
    int (*open) (struct inode *, struct file *);
    int (*release) (struct inode *, struct file *);
    int (*fsync) (struct file *, int datasync);
};

驱动程序

#include <linux/module.h>           //模块头文件
#include <linux/kernel.h>           //内核头文件
#include <linux/init.h>             //内核初始化

#include <linux/fs.h>               //字符设备函数
#include <linux/cdev.h>             //字符设备描述
#include <linux/kdev_t.h>           //系列设备号处理宏

#include <linux/slab.h>             //内存分配头文件
#include <linux/device.h>           //设备类节点头文件

#define DEVICE_NAME     "leds"      //字符设备名称
#define NODE_NAME       "led"

#define DEVICE_MINOR_NUM    2       //字符设备数量

#define DEV_MAJOR   0               //主设备号
#define DEV_MINOR   0               //次设备号，0为自动分配

static int leds_major = DEV_MAJOR;  //主设备号变量
static int leds_minor = DEV_MINOR;  //次设备号变量

static dev_t leds_dev;              //设备号
struct cdev *leds_cdev;             //字符设备结构体变量

static struct class *leds_class;    //类结构体变量
static int leds_open(struct inode *inode, struct file *file)
{
    int ret = 0;
    printk(KERN_EMERG "leds ops open is ok\n");
    return ret;
}

static int leds_release(struct inode *inode, struct file *file)
{
    int ret = 0;
    printk(KERN_EMERG "leds ops release is ok\n");
    return ret;
}

static ssize_t leds_read(struct file *file, char __user *buff, size_t count, loff_t *offp)
{
    int ret = 0;
    printk(KERN_EMERG "leds ops read is ok\n");
    return ret;
}

static ssize_t leds_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
    int ret = 0;
    printk(KERN_EMERG "leds ops write is ok\n");
    return ret;
}

static long leds_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
    long ret = 0;
    printk(KERN_EMERG "%s: cmd = %d, arg = %d\n", __FUNCTION__, cmd, (int)arg);
    return ret;
}   

struct file_operations leds_fops = {
    .owner = THIS_MODULE,
    .open  = leds_open,
    .release = leds_release,
    .read  = leds_read,
    .write = leds_write,
    .unlocked_ioctl = leds_ioctl,
};

static __init int leds_init(void)
{
    int ret = 0;
    int i;
    
    ret = alloc_chrdev_region(&leds_dev, leds_minor, DEVICE_MINOR_NUM, DEVICE_NAME);    //动态分配
    if(ret < 0){
        printk(KERN_EMERG "register_chrdev_region req %d is failed!\n", DEV_MAJOR);
        return ret;
    }
    
    leds_major = MAJOR(leds_dev);   //主设备号
    leds_minor = MINOR(leds_dev);   //次设备号
    
    printk(KERN_EMERG "leds chrdev major=%d, minor=%d\n", leds_major, leds_minor);
    
    leds_class = class_create(THIS_MODULE,DEVICE_NAME);     //类节点创建
    
    leds_cdev = kmalloc(DEVICE_MINOR_NUM * sizeof(struct cdev), GFP_KERNEL);    //申请内存
    if(leds_cdev == NULL)
    {
        printk(KERN_EMERG "kmalloc failed");
        unregister_chrdev_region(leds_dev, DEVICE_MINOR_NUM);
        return -ENOMEM;
    }
    
    //memset(leds_cdev, 0, DEVICE_MINOR_NUM * sizeof(struct dev_cdev));
    
    for(i=0; i<DEVICE_MINOR_NUM; i++){
        
        cdev_init(&leds_cdev[i], &leds_fops);               //字符类设备初始化
        
        leds_cdev[i].owner = THIS_MODULE;
        leds_cdev[i].ops = &leds_fops;
        
        ret = cdev_add(&leds_cdev[i], MKDEV(leds_major, leds_minor+i), 1);  //注册到设备
        
        device_create(leds_class, NULL, MKDEV(leds_major, leds_minor+i), NULL, NODE_NAME"%d", i);   //设备节点创建
        
        if(ret < 0){
            printk(KERN_EMERG "cdev_add %d failed!\n", i);
        }
        else{
            printk(KERN_EMERG "cdev_add %d success!\n", i);
        }
    }
    
    return ret;
}

static __exit void leds_exit(void)
{
    int i;
    for(i=0; i<DEVICE_MINOR_NUM; i++){
        cdev_del(&leds_cdev[i]);                                        //注销设备
        device_destroy(leds_class, MKDEV(leds_major, leds_minor+i));    //注销设备节点
    }
    class_destroy(leds_class);                                          //类节点注销
    kfree(leds_cdev);                                                   //释放内存
    unregister_chrdev_region(leds_dev, DEVICE_MINOR_NUM);               //注销设备号
    printk(KERN_EMERG "leds chrdev exit \n");
}

module_init(leds_init);
module_exit(leds_exit);

MODULE_LICENSE("GPL");

应用程序

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
int main(int argc, char **argv)
{
    int fd,ret=0;
    char *led0 = "/dev/led0";
    char *led1 = "/dev/led1";
    
    if((fd = open(led0, O_RDWR|O_NOCTTY|O_NDELAY))<0){
        printf("open %s failed\n",led0);
        exit(1);
    }
    else{
        printf("open %s success! fd=%d\n", led0, fd);
    }
    close(fd);
    
    if((fd = open(led1, O_RDWR|O_NOCTTY|O_NDELAY))<0){
        printf("open %s failed\n",led1);
        exit(1);
    }
    else{
        printf("open %s success! fd=%d\n", led1, fd);
    }
    close(fd);
    
    return ret;
}

编译

make

加载编译后的模块

insmod leds.ko

查看字符设备节点

ls /dev/l*

执行应用程序

./leds_app 0 0

结束语

以上则为嵌入式Linux字符设备LED及应用程序编写的相关内容。