linux下字符驱动示例helloworld

1：最简单的驱动框架

hello.c

/*************************************************************************
    > File Name: hello.c
    > Author: kayshi
    > Mail: [e-mail]
    > Created Time: Thu 24 Sep 2020 11:25:50 AM CST
 ************************************************************************/

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>

static int hello_init(void)
{
    printk("this is hello\n");
    return 0;
}

static void hello_exit(void)
{
    printk("this is end\n");
}
MODULE_LICENSE("GPL");
module_init(hello_init);
module_exit(hello_exit);

Makefile

ifneq ($(KERNELRELEASE),)
obj-m:=hello.o
$(info "2nd")
else
KDIR := /lib/modules/$(shell uname -r)/build
PWD:=$(shell pwd)
all:
    $(info "1st")
    make -C $(KDIR) M=$(PWD) modules
clean:
    rm -f *.ko *.o *.symvers *.mod.c *.mode.o *.order
endif

加载：
sudo insmod hello.ko

查看：
lsmod

删除：
sudo rmmod hello

查看打印信息：
demsg

2：进行字符设备注册

补全代码hello.c

/*************************************************************************
    > File Name: hello.c
    > Author: kayshi
    > Mail: [e-mail]
    > Created Time: Thu 24 Sep 2020 11:25:50 AM CST
 ************************************************************************/

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>

static int major = 300;
static int minor = 0;
static dev_t devno;
static struct cdev cdev;


static int hello_open(struct inode *inode, struct file *filep)
{
    printk("hello open\n");
    return 0;
}

static struct file_operations hello_ops=
{
    .open = hello_open,
};

static int hello_init(void)
{
    int ret;

    printk("hello_init\n");
    devno = MKDEV(major, minor);
    ret = register_chrdev_region(devno, 1, "hello");
    if(ret < 0)
    {   
        printk("register_chrdev_region faile\n");
                return ret;
    }
    cdev_init(&cdev, &hello_ops);
    ret = cdev_add(&cdev, devno, 1);
    if(ret < 0)
    {
        printk("cdev_add faile \n");
        return ret;
    }
    return 0;
}

static void hello_exit(void)
{
    cdev_del(&cdev);
    unregister_chrdev_region(devno, 1);
    printk("hello_exit\n");
}
MODULE_LICENSE("GPL");
module_init(hello_init);
module_exit(hello_exit);

编译执行后
查看信息
cat /proc/devices

如果再insmod时出现了下面的情况

这是因为代码中的主设备号已经被使用了。把设备号改大一点就行

此时/dev/没有出现设备
需要通过命令

sudo mknod /dev/hello c 300 0

来创建设备，再查看

测试代码

/*************************************************************************
    > File Name: test.c
    > Author: kayshi
    > Mail: [e-mail]
    > Created Time: Thu 24 Sep 2020 02:47:37 PM CST
 ************************************************************************/

#include <stdio.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/types.h>

void main()
{
    int fd; 

    fd = open("/dev/hello", O_RDWR);
    if(fd < 0)
    {   
        perror("open faile \n");
        return ;
    }   
    close(fd);
}

执行测试代码后
再用dmesg查看log信息

hello open被打印，说明hello_open这个函数被调用了

3 添加读写操作

在驱动中添加读写函数。重新生成并insmod

/*************************************************************************
    > File Name: hello.c
    > Author: kayshi
    > Mail: [e-mail]
    > Created Time: Thu 24 Sep 2020 11:25:50 AM CST
 ************************************************************************/

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>

static int major = 300;
static int minor = 0;
static dev_t devno;
static struct cdev cdev;

static ssize_t hello_write(struct file *f, const char __user *u, size_t s, loff_t *l)
{   
    printk("hello write");
    return 0;
}

static ssize_t hello_read(struct file *f, char __user *u, size_t s, loff_t *l)
{   
    printk("hello read");
    return 0;
}

static int hello_open(struct inode *inode, struct file *filep)
{   
    printk("hello open\n");
    return 0;
}

static struct file_operations hello_ops=
{   
    .open = hello_open,
    .write = hello_write
    .read = hello_read,
};

static int hello_init(void)
{
    int ret;

    printk("hello_init\n");
    devno = MKDEV(major, minor);
    ret = register_chrdev_region(devno, 1, "hello");
    if(ret < 0)
    {
        printk("register_chrdev_region faile\n");
        return ret;
    }
    cdev_init(&cdev, &hello_ops);
    ret = cdev_add(&cdev, devno, 1);
    if(ret < 0)
    {
        printk("cdev_add faile \n");
        return ret;
    }
    return 0;
}

static void hello_exit(void)
{
    cdev_del(&cdev);
    unregister_chrdev_region(devno, 1);
    printk("hello_exit\n");
}
MODULE_LICENSE("GPL");
module_init(hello_init);
module_exit(hello_exit)

在测试代码中添加读写测试

/*************************************************************************
    > File Name: test.c
    > Author: kayshi
    > Mail: [e-mail]
    > Created Time: Thu 24 Sep 2020 02:47:37 PM CST
 ************************************************************************/

#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>

void main()
{
    int fd; 
    char buf[8] = {0};

    fd = open("/dev/hello", O_RDWR);
    if(fd < 0)
    {   
        perror("open faile \n");
        return ;
    }   
    write(fd, buf, sizeof(buf));
    read(fd, buf, sizeof(buf));

    close(fd);
}

dmesg查看信息

读写函数的打印信息都出现了