1）struct cdev：在内核中代表一个字符设备驱动（char device，cdev），每一个字符设备驱动都有一个struct cdev结构体变量与之对应，记录该设备驱动的相关信息，主要包括设备号dev_t dev和设备操作函数集const struct file_operations *ops。定义如下：

struct cdev {
 struct kobject kobj;
 struct module *owner;
 const struct file_operations *ops;
 struct list_head list;
 dev_t dev;
 unsigned int count;
};

2）struct file_operations：定义了设备驱动程序与用来访问操作内核之间的接口，该结构体定义的函数指来访用来问实际的硬件设备，不同的硬件设备具有不同的读写函数。

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 (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
	int (*readdir) (struct file *, void *, filldir_t);
	unsigned int (*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 *);
	int (*open) (struct inode *, struct file *);
	int (*flush) (struct file *, fl_owner_t id);
	int (*release) (struct inode *, struct file *);
	int (*fsync) (struct file *, int datasync);
	int (*aio_fsync) (struct kiocb *, 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 **);
};

 3）struct  inode：表示一个文件节点，记录一个文件固有的通用的信息，任何一个文件都有这个结构体变量。

struct inode {
	struct hlist_node	i_hash;
	struct list_head	i_list;		/* backing dev IO list */
	struct list_head	i_sb_list;
	struct list_head	i_dentry;
	unsigned long		i_ino;
	atomic_t		i_count;
	unsigned int		i_nlink;
	uid_t			i_uid;
	gid_t			i_gid;
	dev_t			i_rdev;
	unsigned int		i_blkbits;
	u64			i_version;
	loff_t			i_size;
#ifdef __NEED_I_SIZE_ORDERED
	seqcount_t		i_size_seqcount;
#endif
	struct timespec		i_atime;
	struct timespec		i_mtime;
	struct timespec		i_ctime;
	blkcnt_t		i_blocks;
	unsigned short          i_bytes;
	umode_t			i_mode;
	spinlock_t		i_lock;	/* i_blocks, i_bytes, maybe i_size */
	struct mutex		i_mutex;
	struct rw_semaphore	i_alloc_sem;
	const struct inode_operations	*i_op;
	const struct file_operations	*i_fop;	/* former ->i_op->default_file_ops */
	struct super_block	*i_sb;
	struct file_lock	*i_flock;
	struct address_space	*i_mapping;
	struct address_space	i_data;
#ifdef CONFIG_QUOTA
	struct dquot		*i_dquot[MAXQUOTAS];
#endif
	struct list_head	i_devices;
	union {
		struct pipe_inode_info	*i_pipe;
		struct block_device	*i_bdev;
		struct cdev		*i_cdev;
	};

4）struct file：表示一个已经打开的文件，记录打开文件的属性，包括读写属性，linux中一切皆文件，但是文件一般分为磁盘文件和特殊文件，而这个特殊文件就是设备文件，其中所有的外围硬件设备都当作设备文件进行处理。

struct file {
	/*
	 * fu_list becomes invalid after file_free is called and queued via
	 * fu_rcuhead for RCU freeing
	 */
	union {
		struct list_head	fu_list;
		struct rcu_head 	fu_rcuhead;
	} f_u;
	struct path		f_path;
#define f_dentry	f_path.dentry
#define f_vfsmnt	f_path.mnt
	const struct file_operations	*f_op;
	spinlock_t		f_lock;  /* f_ep_links, f_flags, no IRQ */
#ifdef CONFIG_SMP
	int			f_sb_list_cpu;
#endif
	at