如何将Ubuntu编译的字符设备成？

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_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)/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 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# 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