前言

创建一个简单的字符设备驱动程序。

​ 本文命令的运行基本上都需要root权限，使用root账号，或者在命令前面加上sudo。

​ 如果你使用ssh远程连接的服务器进行代码编写。那么不要在root用户下创建文件或者文件夹。这会导致你ssh连接vscode编写代码的权限问题。可以在普通用户创建好所有的文件，然后编写。

代码

驱动程序

hello_driver.c

#include <linux/types.h> #include <linux/init.h> #include <linux/interrupt.h> #include <linux/mm.h> #include <linux/slab.h> #include <linux/spinlock.h> #include <linux/module.h> #include <linux/device.h> #include <linux/cdev.h>     dev_t hello_devid; struct cdev hello_cdev; int hello_major = 0; int hello_minor;     uint8_t kernel_buffer[1024] = {0}; static struct class *hello_class;       static int hello_world_open(struct inode * inode, struct file * file) { 	printk("hello_world_openrn"); 	return 0; }   static int hello_world_release (struct inode * inode, struct file * file) { 	printk("hello_world_releasern"); 	return 0; }   static ssize_t hello_world_read (struct file * file, char __user * buffer, size_t size, loff_t * ppos) { 	printk("hello_world_read size:%ldrn",size); 	copy_to_user(buffer,kernel_buffer,size); 	return size; }   static ssize_t hello_world_write(struct file * file, const char __user * buffer, size_t size, loff_t *ppos) { 	printk("hello_world_write size:%ldrn",size); 	copy_from_user(kernel_buffer,buffer,size); 	return size; }     static const struct file_operations hello_world_fops = { 	.owner		= THIS_MODULE, 	.open		= hello_world_open, 	.release = hello_world_release, 	.read		= hello_world_read, 	.write	= hello_world_write, };     static int __init hello_driver_init(void) { 	int ret; 	printk("hello_driver_initrn");   	alloc_chrdev_region(&hello_devid, 0, 1, "hello"); 	hello_major = MAJOR(hello_devid); 	hello_minor = MINOR(hello_devid); 	printk("hello driver major=%d,minor=%drn",hello_major, hello_minor);	   	hello_cdev.owner = THIS_MODULE; 	cdev_init(&hello_cdev, &hello_world_fops); 	cdev_add(&hello_cdev, hello_devid, 1); 	 	hello_class = class_create(THIS_MODULE,"hello_class");   	device_create(hello_class,NULL,hello_devid,NULL,"hello"); /* /dev/hello */   	return 0; }   static void __exit hello_driver_cleanup(void) { 	printk("hello_driver_cleanuprn"); 	cdev_del(&hello_cdev); 	unregister_chrdev_region(hello_devid, 1); 	 	device_destroy(hello_class,hello_devid); 	class_destroy(hello_class); 	 }     module_init(hello_driver_init); module_exit(hello_driver_cleanup); MODULE_LICENSE("GPL");  

Makefile文件

KERNELDIR := /lib/modules/$(shell uname -r)/build CURRENT_PATH := $(shell pwd) obj-m := hello_driver.o  KBUILD_CFLAGS   += -Wno-unused-result -Wno-unused-variable build: kernel_modules   kernel_modules: 	$(MAKE) ${CFLAGS} -C $(KERNELDIR) M=$(CURRENT_PATH) modules 	$(CROSS_COMPILE)gcc -o test_app test_app.c clean: 	$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean 	rm -rf test_app 

测试程序

test_app.c

#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdlib.h> #include <string.h> #include <stdint.h>  uint8_t buffer[512] = {0};   int main(int argc, char *argv[]) { 	int fd; 	int ret; 	 	fd  = open(argv[1], O_RDWR);     if(!fd)     {         printf("everthing is errorn");     }   	if(!strcmp("read",argv[2])) 	{ 		printf("read data from kernelrn"); 		ret = read(fd,buffer,sizeof(buffer)); 		printf("ret len:%d data:%srn",ret,buffer); 	}   	if(!strcmp("write",argv[2])) 	{ 		printf("write data to kernel %s len:%ldrn",argv[3],strlen(argv[3])); 		ret = write(fd,argv[3],strlen(argv[3])); 		printf("ret len:%drn",ret); 	}   	 	close(fd);   	 } 

编译

执行make命令编译

root@ubuntu:/home/dong/workspace/drivercode# make make  -C /lib/modules/5.19.0-38-generic/build M=/home/dong/workspace/drivercode modules make[1]: Entering directory '/usr/src/linux-headers-5.19.0-38-generic' warning: the compiler differs from the one used to build the kernel   The kernel was built by: x86_64-linux-gnu-gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0   You are using:           gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0   CC [M]  /home/dong/workspace/drivercode/hello_driver.o   MODPOST /home/dong/workspace/drivercode/Module.symvers   CC [M]  /home/dong/workspace/drivercode/hello_driver.mod.o   LD [M]  /home/dong/workspace/drivercode/hello_driver.ko   BTF [M] /home/dong/workspace/drivercode/hello_driver.ko Skipping BTF generation for /home/dong/workspace/drivercode/hello_driver.ko due to unavailability of vmlinux make[1]: Leaving directory '/usr/src/linux-headers-5.19.0-38-generic' gcc -o test_app test_app.c 

会生成hello_driver.ko文件和test_app

加载模块

insmod hello_driver.ko

卸载模块

rmmod hello_driver

查看模块

lsmod |grep hello_driver

运行测试

创建设备文件

这个文件不是随便创造的，会分配设备号，如果不使用分配的设备号创建会出现读写错误。

​ 每一次加载或者卸载模块都会有dmesg信息。

​ 使用dmesg -c清除信息。加载模块，使用dmesg查看模块信息。

root@ubuntu:/home/dong/workspace/drivercode# dmesg [164284.337396] hello_driver_init [164284.337399] hello driver major=238,minor=0 

我的设备主设备号就是238，从设备号是0

创建设备文件命令

mknod /dev/hello c 238 0

测试

读 ： ./test_app /dev/hello read

写： ./test_app /dev/hello write 需要写入的内容