Linux文件系统与设备驱动

应用程序与VFS（Virtual FileSystem）之间的接口是系统调用。

VFS与文件系统及设备文件之间的接口是file_operation 结构体成员函数。（结构成员函数过多，基本上编程用到的有.read  .write .open .owner = THIS_MODULE)。

在对file_opreation 结构体成员函数进行编写时，主要的用到的file ，incode这两个结构体。

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
	atomic_long_t		f_count;
	unsigned int 		f_flags;
	fmode_t			f_mode;
	loff_t			f_pos;
	struct fown_struct	f_owner;
	const struct cred	*f_cred;
	struct file_ra_state	f_ra;

	u64			f_version;
#ifdef CONFIG_SECURITY
	void			*f_security;
#endif
	/* needed for tty driver, and maybe others */
	void			*private_data;

#ifdef CONFIG_EPOLL
	/* Used by fs/eventpoll.c to link all the hooks to this file */
	struct list_head	f_ep_links;
#endif /* #ifdef CONFIG_EPOLL */
	struct address_space	*f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
	unsigned long f_mnt_write_state;
#endif
};
           

在file结构体里f_mode读/写模式，f_flags标志是设备驱动的实际考虑要点。

    void            *private_data;//用来指向设备驱动自定义用来描述设备的结构体。

struct inode {
	/* RCU path lookup touches following: */
	umode_t			i_mode;
	uid_t			i_uid;
	gid_t			i_gid;
	const struct inode_operations	*i_op;
	struct super_block	*i_sb;

	spinlock_t		i_lock;	/* i_blocks, i_bytes, maybe i_size */
	unsigned int		i_flags;
	unsigned long		i_state;
#ifdef CONFIG_SECURITY
	void			*i_security;
#endif
	struct mutex		i_mutex;


	unsigned long		dirtied_when;	/* jiffies of first dirtying */

	struct hlist_node	i_hash;
	struct list_head	i_wb_list;	/* backing dev IO list */
	struct list_head	i_lru;		/* inode LRU list */
	struct list_head	i_sb_list;
	union {
		struct list_head	i_dentry;
		struct rcu_head		i_rcu;
	};
	unsigned long		i_ino;
	atomic_t		i_count;
	unsigned int		i_nlink;
	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;
	struct rw_semaphore	i_alloc_sem;
	const struct file_operations	*i_fop;	/* former ->i_op->default_file_ops */
	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;
	};

	__u32			i_generation;

#ifdef CONFIG_FSNOTIFY
	__u32			i_fsnotify_mask; /* all events this inode cares about */
	struct hlist_head	i_fsnotify_marks;
#endif

#ifdef CONFIG_IMA
	atomic_t		i_readcount; /* struct files open RO */
#endif
	atomic_t		i_writecount;
#ifdef CONFIG_FS_POSIX_ACL
	struct posix_acl	*i_acl;
	struct posix_acl	*i_default_acl;
#endif
	void			*i_private; /* fs or device private pointer */
};
           

在VFS iNode结构体包含文件访问权限，属性，组，大小，生成时间，访问时间，最后修改时间等信息。是文件系统连接任何子目录、文件的桥梁。

    dev_t            i_rdev;//i_rdev字段包含设备编号、分为主设备编号，和次设备编号。前者为高12位，后者为低20位。

从一个inode中获取到主设备号，次设备号。

unsigned int iminor(struct incode  *inode);

unsigned int imajor(struct incode  *inode);