linux字符设备驱动开发入门

1.基本步骤

graph LR;
	a("申请设备号")-->b("注册设备号")-->c("设置设备对应的file_operations")-->d("加入到内核链表")
	ab("MKDEV(major,minor)")-->ac("register_chrdev_region()")-->ad("cdev_init()")-->ae("cdev_add()")

2.实例

//驱动程序源码
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#define BUFFER_SIZE;
struct mychar
{
    dev_t devnum;
    unsigned long curlen;
    struct dev mydev;
    char buffer[BUFFER_SIZE];
}mychardev;
//设备打开函数
static int mychar_open(struct inode *node,struct file *filp)
{
    //获取结构体地址
    filp->private_data = (void*)container_of(node->i_cdev,struct mychar,mydev);
    return 0;
}
static int mychar_close(struct inode *node,struct file *filp)
{
    return 0;
}
static long mychar_read(struct file *filp,char __user *buffer,long unsigned int count,long long int *pos)
{
    return 0;
}
static long mychar_write(struct file *filp,const char __user *buffer,long unsigned int count,long long int *pos)
{
    return 0;
}
static long mychar_ioctl(struct file *filp,unsigned int cmd,unsigned long arg)
{
    return 0;
}
int __init my_init(void)
{
    //申请设备号
    mychardev.devnum = MKDEV(11,256);
    //注册设备号
    if(register_chrdev_region(mychardev.devnum,1,"mychar")!=0)
    {
        if(alloc_chrdev_region(&mychardev.devnum,256,1,"mychar")!=0)
        {
            printk("register devnum error!\n");
            return 0;
        }
    }
    struct file_operations fops=
    {
        .owner = THIS_MODULE,
        .open = mychar_open,
        .release = mychar_close,
        .read = mychar_read,
        .write = mychar_write,
        .unlocked_ioctl = mychar_ioctl,
    }
    //设置对应的文件操作函数
    cdev_init(&mychardev.mydev,&fops);
    //加入到内核链表
    cdev_add(&mychardev.mydev,mychardev.devnum,1);
    return 0;
}
void __exit my_exit(void)
{
    cdev_del(&mychardev.mydev);
    unregister_chrdev_region(mychardev.devnum,1);
    return;
}

module_init(my_init);
module_exit(my_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("404NotFound");
MODULE_DESCRIPTION("just a char devices driver!");

//项目的Makefile
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD ?= $(shell pwd)
modules:
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
	rm *.o *.mod *.symvers
obj-m += main.o