ubuntu编译字符设备

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 #include #include #include #include #include #include #include #include   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_open\r\n");return 0;} static int hello_world_release (struct inode * inode, struct file * file){printk("hello_world_release\r\n");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:%ld\r\n",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:%ld\r\n",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_init\r\n"); alloc_chrdev_region(&hello_devid, 0, 1, "hello");hello_major = MAJOR(hello_devid);hello_minor = MINOR(hello_devid);printk("hello driver major=%d,minor=%d\r\n",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_cleanup\r\n");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)/buildCURRENT_PATH := $(shell pwd)obj-m := hello_driver.oKBUILD_CFLAGS   += -Wno-unused-result -Wno-unused-variablebuild: kernel_modules kernel_modules:$(MAKE) ${CFLAGS} -C $(KERNELDIR) M=$(CURRENT_PATH) modules$(CROSS_COMPILE)gcc -o test_app test_app.cclean:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) cleanrm -rf test_app

测试程序

test_app.c

#include #include #include #include #include #include #include #include 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 error\n");    } if(!strcmp("read",argv[2])){printf("read data from kernel\r\n");ret = read(fd,buffer,sizeof(buffer));printf("ret len:%d data:%s\r\n",ret,buffer);} if(!strcmp("write",argv[2])){printf("write data to kernel %s len:%ld\r\n",argv[3],strlen(argv[3]));ret = write(fd,argv[3],strlen(argv[3]));printf("ret len:%d\r\n",ret);} close(fd); }

编译

执行make命令编译

root@ubuntu:/home/dong/workspace/drivercode# makemake  -C /lib/modules/5.19.0-38-generic/build M=/home/dong/workspace/drivercode modulesmake[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.koSkipping BTF generation for /home/dong/workspace/drivercode/hello_driver.ko due to unavailability of vmlinuxmake[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