Linux中驱动程序的分析

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我是靠谱客的博主能干鱼，这篇文章主要介绍Linux中驱动程序的分析，现在分享给大家，希望可以做个参考。

一、linux驱动的层次结构

二、驱动程序分析

内核中字符设备结构体的定义

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struct cdev 
{
struct kobject kobj;          // 每个 cdev 都是一个 kobject   
struct module *owner;        // 指向实现驱动的模块    
const struct file_operations *ops;    // 操纵这个字符设备文件的方法  
struct list_head list;        // 与 cdev 对应的字符设备文件的 inode->i_devices 的链表头
dev_t dev;                   // 起始设备编号  
unsigned int count;        // 设备号范围大小
};

Linux内核对文件操作file_operations结构体的定义

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struct file_operations {
       struct module *owner;
       loff_t (*llseek) (struct file *, loff_t, int);
       ssize_t (*read) (struct file *, char *, size_t, loff_t *);
       ssize_t (*write) (struct file *, const char *, size_t, loff_t *);
       int (*readdir) (struct file *, void *, filldir_t);
       unsigned int (*poll) (struct file *, struct poll_table_struct *);
       int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
       int (*mmap) (struct file *, struct vm_area_struct *);
       int (*open) (struct inode *, struct file *);
       int (*flush) (struct file *);
       int (*release) (struct inode *, struct file *);
       int (*fsync) (struct file *, struct dentry *, int datasync);
       int (*fasync) (int, struct file *, int);
       int (*lock) (struct file *, int, struct file_lock *);
    ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
          loff_t *);
    ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
          loff_t *);
    };

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struct file_operations {
       struct module *owner;
       loff_t (*llseek) (struct file *, loff_t, int);
       ssize_t (*read) (struct file *, char *, size_t, loff_t *);
       ssize_t (*write) (struct file *, const char *, size_t, loff_t *);
       int (*readdir) (struct file *, void *, filldir_t);
       unsigned int (*poll) (struct file *, struct poll_table_struct *);
       int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
       int (*mmap) (struct file *, struct vm_area_struct *);
       int (*open) (struct inode *, struct file *);
       int (*flush) (struct file *);
       int (*release) (struct inode *, struct file *);
       int (*fsync) (struct file *, struct dentry *, int datasync);
       int (*fasync) (int, struct file *, int);
       int (*lock) (struct file *, int, struct file_lock *);
    ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
          loff_t *);
    ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
          loff_t *);
    };

file_operations 成员大部分是文件指针，设备不支持的指针置为NULL。驱动程序的文件操作编写如下

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struct file_operations xxx_fops ={
.open = xxx_open,//xxx_open()函数是自己编写的对具体设备的打开操作
.read = xxx_read,
.write = xxx_write,
.release = xxx_release,

};

字符设备cdev结构体的初始化(静态),可单独写在一个函数xxx_setup_cdev()中，也可写在模块加载函数xxx_init()中。

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cdev_init(&cdev,&fops);
cdev.owner = THIS_MODULE;

字符设备驱动模块加载与卸载的模板

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//设备结构体
struct xxx_dev{
struct cdev cdev;
...
}xxx_dev;
//设备驱动模块加载函数
static int __init xxx_init(void){
    cdev_init(&xxx_dev.cdev,&xxx_fops);//初始化cdev（静态）
    xxx_dev.cdev.owner = THIS_MODULE;
    dev_t xxx_dev_no =MKDEV(xxx_major,0);
   //获取字符设备号
    if (xxx_major) {
     register_chrdev_region(xxx_dev_no,1,DEV_NAME);
    }
    else{
        alloc_chrdev_region(&xxx_dev_no,0,DEV_NAME);
    }
//注册设备
   ret = cdev_add(&xxx_dev.cdev,xxx_dev_no,1)//参数xxx_dev_no是设备响应的第一个设备号,参数 1表示设备相关联的设备号的数目
    return 0;
}
//设备驱动卸载模块函数
static void __exit xxx_exit(void){
    unregister_chrdev_region(xxx_dev_no,1);//释放占用的设备号
    cdev_del(&xxx_dev.cdev)//注销设备
   
}
module_init(xxx_init);
module_exit(xxx_exit);
......