Linux字符设备注册

结构体原型

struct cdev { 
    struct kobject kobj;                  //kobject对象
    struct module *owner;                 //THIS_MODULE,类似于C++中的this指针
    const struct file_operations *ops;    //操作方法集
    struct list_head list; 
    dev_t dev;                            //设备号（U32 32bit无符号整型）
    unsigned int count;                   //设备计数
};

结构体空间开辟

struct cdev *cdev_alloc(void)

结构体空间初始化

/*
参数：
    cdev设备结构体指针，初始化设备结构体指针；
    fops：设备的操作方法集；
PS：为了保证内核空间的安全性，所以需要使用初始化函数实现
*/
void cdev_init(struct cdev *cdev, const struct file_operations *fops)

操作方法集的结构体

struct file_operations {
/* 一般传THIS_MODULE */
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 *);
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 *, loff_t, loff_t, 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);
};

机构体注册

/**
 * [cdev_add 将字符设备结构体添加到内核系统的驱动管理单元(链表)中，由内核进行统一调度]
 * @param  p     [指向的字符设备注册结构体]
 * @param  dev   [字符设备号]
 * @param  count [字符设备个数]
 * @return       [ 成功返回0,失败返回错误号]
 */
int cdev_add(struct cdev *p, dev_t dev, unsigned count)

字符设备移除

/*将字符设备结构体从内核中移除，并释放结构体空间*/
void cdev_del(struct cdev *p)

实例

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>
#include <linux/cdev.h>

MODULE_LICENSE("GPL");


/* 定义字符设备的操作方法集 */
int my_open(struct inode *inodep, struct file *filep)
{
    printk(KERN_INFO "%s\n", __func__);

    return 0;
}

int my_release(struct inode *inodep, struct file *filep)
{
    printk(KERN_INFO "%s\n", __func__);

    return 0;
}

static dev_t dev;/* 定义设备号变量 */
static unsigned int count = 1;

/* 定义字符设备结构体指针 */
struct cdev *cdevp;
/* 定义字符设备的操作方法集结构体 */
struct file_operations fops =
{
    .owner = THIS_MODULE,
    .open = my_open,
    .release = my_release
};



/* 定义模块加载函数 */
static int __init my_module_init(void)
{
    int ret;

    /* 申请设备编号：采用动态申请方式 */
    ret = alloc_chrdev_region(&dev, 0, count, "mychar");
    if (ret != 0)
    {
        printk(KERN_ERR "register_chrdev_region: ret = %d\n", ret);
        return ret;
    }
    printk(KERN_INFO "register_chrdev_region major:%d,minor:%d\n", MAJOR(dev), MINOR(dev));

    /* 设备注册：将设备添加到内核驱动管理链表中，然后由系统进行统一调度 */
    /* 开辟字符设备结构体空间 */
    cdevp = cdev_alloc();
    if (cdevp == NULL)
    {
        ret = -ENOMEM;
        goto mychar_err0;
    }

    /* 初始化结构体成员 */
    cdev_init(cdevp, &fops);

    /* 将字符设备结构体cdev添加到system中，由内核统一调度 */
    ret = cdev_add(cdevp, dev, count);
    if (ret < 0)
    {
        goto mychar_err1;
    }

    printk(KERN_INFO "cdev register success\n");

    return 0;

mychar_err1:
    /* 释放字符设备结构体 */
    cdev_del(cdevp);
mychar_err0:
    /* 释放设备号 */
    unregister_chrdev_region(dev, count);
    return ret;
}

/* 定义模块卸载函数 */
static void __exit my_module_exit(void)
{
    /* 释放字符设备结构体 */
    cdev_del(cdevp);

    /* 释放设备号 */
    unregister_chrdev_region(dev, count);
}

/* 声明模块的加载入口 */
module_init(my_module_init);
/* 声明模块的卸载入口 */
module_exit(my_module_exit);