Linux文件系统

最新推荐文章于 2022-06-06 17:24:22 发布

原创最新推荐文章于 2022-06-06 17:24:22 发布

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首先要从fs.h头文件开始，file的定义为：

<span style="font-size:14px;">	/*
	 * 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 */
	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;
	struct list_head	f_tfile_llink;
#endif /* #ifdef CONFIG_EPOLL */
	struct address_space	*f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
	unsigned long f_mnt_write_state;
#endif
};</span>

其中struct path的定义为：

<span style="font-size:14px;">struct path {
	struct vfsmount *mnt;
	struct dentry *dentry;
</span><span style="font-family:KaiTi_GB2312;font-size:14px;">};
</span>

dentry的定义为：

<span style="font-size:14px;">struct dentry {
	atomic_t d_count;
	unsigned int d_flags;		/* protected by d_lock */
	spinlock_t d_lock;		/* per dentry lock */
	int d_mounted;
	struct inode *d_inode;		/* Where the name belongs to - NULL is
					 * negative */
	/*
</span><span style="font-size:14px;">	 * The next three fields are touched by __d_lookup.  Place them here
	 * so they all fit in a cache line.
	 */
	struct hlist_node d_hash;	/* lookup hash list */  通过查询哈希表的方式，可以比较快的找到一个inode。
	struct dentry *d_parent;	/* parent directory */
	struct qstr d_name;

	struct list_head d_lru;		/* LRU list */
	/*
	 * d_child and d_rcu can share memory
	 */
	union {
		struct list_head d_child;	/* child of parent list */
	 	struct rcu_head d_rcu;
	} d_u;
	struct list_head d_subdirs;	/* our children */
	struct list_head d_alias;	/* inode alias list */
	unsigned long d_time;		/* used by d_revalidate */
	const struct dentry_operations *d_op;
	struct super_block *d_sb;	/* The root of the dentry tree */
	void *d_fsdata;			/* fs-specific data */

	unsigned char d_iname[DNAME_INLINE_LEN_MIN];	/* small names */
};
</span>

dentry里有一个结构体inode，记录了file的重要相关信息

<span style="font-size:14px;">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;     //link数
	uid_t			i_uid;       //用户，组信息，
	gid_t			i_gid;
	dev_t			i_rdev;
	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 int		i_blkbits;
	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;            //默认文件操作。
	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;
	};

	__u32			i_generation;

#ifdef CONFIG_FSNOTIFY
	__u32			i_fsnotify_mask; /* all events this inode cares about */
	struct hlist_head	i_fsnotify_mark_entries; /* fsnotify mark entries */
#endif

#ifdef CONFIG_INOTIFY
	struct list_head	inotify_watches; /* watches on this inode */
	struct mutex		inotify_mutex;	/* protects the watches list */
#endif

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

	unsigned int		i_flags;

	atomic_t		i_writecount;
#ifdef CONFIG_SECURITY
	void			*i_security;
#endif
#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 */
};</span>

里面有个关键成员const struct file_operations *i_fop;，定义为:

<span style="font-size:14px;">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 *);
	int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long);
	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 *, struct dentry *, 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 **);
};</span>