设计字符设备

文件系统调用系统IO的内核处理过程

在Linux文件系统管理中，当应用程序调用open函数时，内核会根据文件路径找到文件的索引结点（inode），为文件分配文件描述符和文件对象，并根据打开模式和权限等参数进行相应的操作和设置。

 

 

硬件层原理

思路：把底层寄存器配置操作放在文件操作接口里，新建一个文件绑定该文件操作接口，应用程序通过操作指定文件来设置底层寄存器。

基本接口实现：查原理图，数据手册，确定底层需要配置的寄存器。类似于裸机开发。实现一个文件的底层操作接口，这是文件的基本特征。

struct file_operations存放在ebf-buster-linux/include/linux/fs.h。

struct file_operations {
        struct module *owner;
        loff_t (*llseek) (struct file *, loff_t, int);
        ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
        ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
        ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
        ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
        int (*iterate) (struct file *, struct dir_context *);
        int (*iterate_shared) (struct file *, struct dir_context *);
        __poll_t (*poll) (struct file *, struct poll_table_struct *);
        long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
        long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
        int (*mmap) (struct file *, struct vm_area_struct *);
        unsigned long mmap_supported_flags;
        int (*open) (struct inode *, struct file *);
        int (*flush) (struct file *, fl_owner_t id);
        int (*release) (struct inode *, struct file *);
        int (*fsync) (struct file *, loff_t, loff_t, int datasync);
        int (*fasync) (int, struct file *, int);
        int (*lock) (struct file *, int, struct file_lock *);
        ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
        unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
        int (*check_flags)(int);
        int (*flock) (struct file *, int, struct file_lock *);
        ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
        ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
        int (*setlease)(struct file *, long, struct file_lock **, void **);
        long (*fallocate)(struct file *file, int mode, loff_t offset, loff_t len);
        void (*show_fdinfo)(struct seq_file *m, struct file *f);
#ifndef CONFIG_MMU
        unsigned (*mmap_capabilities)(struct file *);
#endif
        ssize_t (*copy_file_range)(struct file *, loff_t, struct file *, loff_t, size_t, unsigned int);
        int (*clone_file_range)(struct file *, loff_t, struct file *, loff_t, u64);
        int (*dedupe_file_range)(struct file *, loff_t, struct file *, loff_t, u64);
        int (*fadvise)(struct file *, loff_t, loff_t, int);
} __randomize_layout;

 

驱动层原理

把file_operations文件操作接口注册到内核，内核通过主次设备号来记录它。

构造驱动基本对象：struct cdev，里面记录具体的file_operations。

cdev_init()　　//把用户构建的file_operations结构体记录在内核驱动的基本对象

 

两个Hash表（帮助找到cdev结构体）

chrdevs：登记设备号。

__register_chrdev_region()

cdev_map->probe：保存驱动基本对象struct cdev。

cdev_add()

 

文件系统层原理

mknod + 主次设备号

构建一个新的设备文件，通过主次设备号在cdev_map中找到cdev->file_operations，把cdev->file_operations绑定到新的设备文件中。

到这一步，应用程序就可以使用open()、write()、read()等函数来控制设备文件了。

 

 

设备号的组成与哈希表