视频资料https://www.bilibili.com/video/BV18SE26cEjn?spm_id_from333.788.videopod.sectionsvd_source92b7efa4daa5bb4fdcdc9f2db97c307bp4代码https://github.com/Johannes4Linux/Linux_Driver_Tutoriallesson7 字符设备的打开和释放lesson8 字符设备的读取和写入其实这两课和lesson5程序很接近不过Johannes 在内核层之外还提供了应用层测试的例程。lesson7 内核层 hello_cdev.c#include linux/module.h #include linux/init.h #include linux/fs.h static int major; //inode 表示内核设备文件的结构体靠它来获得主/附设备号flip 代表打开的设备文件 static int my_open(struct inode *inode, struct file *filp) { //主设备号 imajor(inode) iminor(inode) imajor/iminor 都是宏 pr_info(hello_cdev - Major: %d, Minor %d\n, imajor(inode), iminor(inode)); //当前打开文件的位置 pr_info(hello_cdev - filp-f_pos: %lld\n, filp-f_pos); //设备文件的权限 ls -lh 命令里面的 rwx pr_info(hello_cdev - filp-f_mode: 0x%x\n, filp-f_mode); //设备文件的标志位 比如层test.c 里面的 O_RDWR/O_WRONLY 等 pr_info(hello_cdev - filp-f_flags: 0x%x\n, filp-f_flags); return 0; } static int my_release(struct inode *inode, struct file *filp) { pr_info(hello_cdev - File is closed\n); return 0; } //设备文件支持的设备操作这里只有open/release 操作 static struct file_operations fops {//实例化fops .open my_open, .release my_release, }; static int __init my_init(void) { major register_chrdev(0, hello_cdev, fops);//注册字符设备 if (major 0) { pr_err(hello_cdev - Error registering chrdev\n); return major; } pr_info(hello_cdev - Major Device Number: %d\n, major); return 0; } static void __exit my_exit(void) { unregister_chrdev(major, hello_cdev); } module_init(my_init); module_exit(my_exit); MODULE_LICENSE(GPL); MODULE_AUTHOR(Johannes 4Linux); MODULE_DESCRIPTION(A sample driver for registering a character device);和lesson5 对比十分类似lesson5 只实例化了.read 读这里有实例化.open/.release视频开始的9分钟对于设备文件这些做了相关说明。视频第十分钟做了个应用层的程序test.c说明看看代码就行略过。#include stdio.h #include stdlib.h #include unistd.h #include fcntl.h int main(int argc, char **argv) { int fd; if (argc 2) { printf(I need the file to open as an argument!\n); return 0; } fd open(argv[1], O_RDONLY); if (fd 0) { perror(open); return fd; } close (fd); fd open(argv[1], O_RDWR | O_SYNC); if (fd 0) { perror(open); return fd; } close (fd); fd open(argv[1], O_WRONLY | O_NONBLOCK); if (fd 0) { perror(open); return fd; } close (fd); return 0; }两个程序都写完了视频开始编译驱动程序insmod之后mknod /dev/hello0 从236 0 mknod /dev/hello0 236 10 ; 这就造了两个字符设备 /dev/hello0 ,主设备号236,次设备号分别是0,10最后在应用层跑测试分别做这两个字符设备打印不同的次设备号不同模式表明测试程序成功。mknod 生成设备文件现在已经不推荐了不过linux还保留这个方法。这几个课程加起来就是对字符设备常用的操作开关读写的操作构成了字符设备的开发架构。我认为字符设备其实都可以理解为在这个架构上开发的。综合lesson3/lesson7 仿照写一个字符设备控制led开关的程序#include linux/module.h #include linux/init.h #include linux/fs.h #include linux/gpio/consumer.h static int major; static struct gpio_desc *led; #define IO_LED 21 #define IO_OFFSET 0 static int my_open(struct inode *inode, struct file *filp) { int status; led gpio_to_desc(IO_LED IO_OFFSET); if (!led) { printk(gpioctrl - Error getting pin %d\n, IO_LED); return -ENODEV; } status gpiod_direction_output(led, 0); if (status) { printk(gpioctrl - Error setting pin %d to output\n, IO_LED); return status; } gpiod_set_value(led, 1); return 0; } static int my_release(struct inode *inode, struct file *filp) { gpiod_set_value(led, 0); pr_info(hello_cdev - File is closed\n); return 0; } static struct file_operations fops { .open my_open, .release my_release, }; static int __init my_init(void) { major register_chrdev(0, hello_cdev, fops); if (major 0) { pr_err(hello_cdev - Error registering chrdev\n); return major; } pr_info(hello_cdev - Major Device Number: %d\n, major); return 0; } static void __exit my_exit(void) { unregister_chrdev(major, hello_cdev); } module_init(my_init); module_exit(my_exit); MODULE_LICENSE(GPL); MODULE_AUTHOR(DOK); MODULE_DESCRIPTION(A sample driver for led);lesson8 代码#include linux/module.h #include linux/init.h #include linux/fs.h static int major; static char text[64];//文本缓冲区 //flip 打开的设备文件 user_buf 数据空指针本例没用 len 缓冲区长度 off 文件位置偏移里 static ssize_t my_read(struct file *filp, char __user *user_buf, size_t len, loff_t *off) { /* not_copied 从应用层读取的字符长度 to_copy (len *off) sizeof(text) ? len : (sizeof(text) - *off) 计算需要复制的可复制字符长度确保文本缓冲区位置不溢出 delta to_copy-not_copied 文本指针移动长度 */ int not_copied, delta, to_copy (len *off) sizeof(text) ? len : (sizeof(text) - *off); pr_info(hello_cdev - Read is called, we want to read %ld bytes, but actually only copying %d bytes. The offset is %lld\n, len, to_copy, *off); if (*off sizeof(text)) return 0; //复制文本缓冲区内容到用户空间user_buf文本缓冲区 text(*off)文本当前位置 to_copy 复制长度 not_copied copy_to_user(user_buf, text[*off], to_copy); delta to_copy - not_copied; if (not_copied) pr_warn(hello_cdev - Could only copy %d bytes\n, delta); *off delta; return delta; } static ssize_t my_write(struct file *filp, const char __user *user_buf, size_t len, loff_t *off) { int not_copied, delta, to_copy (len *off) sizeof(text) ? len : (sizeof(text) - *off); pr_info(hello_cdev - Write is called, we want to write %ld bytes, but actually only copying %d bytes. The offset is %lld\n, len, to_copy, *off); if (*off sizeof(text)) return 0; not_copied copy_from_user(text[*off], user_buf, to_copy); delta to_copy - not_copied; if (not_copied) pr_warn(hello_cdev - Could only copy %d bytes\n, delta); *off delta; return delta; } static struct file_operations fops { .read my_read, .write my_write }; static int __init my_init(void) { //动态配置字符设备不需要设备号 major register_chrdev(0, hello_cdev, fops); if (major 0) { pr_err(hello_cdev - Error registering chrdev\n); return major; } printk(hello_cdev - Major Device Number: %d\n, major); return 0; } static void __exit my_exit(void) { unregister_chrdev(major, hello_cdev); } module_init(my_init); module_exit(my_exit); MODULE_LICENSE(GPL); MODULE_AUTHOR(Johannes 4Linux); MODULE_DESCRIPTION(A sample driver for registering a character device);重点了解 copy_to_user /copy_from_user 两个函数实现应用层的读写控制内核层这个和正点原子里面led 读写驱动很像了