文件系统学习初探（1）

linux提供文件系统抽象层接口即VFS，定义了文件系统的基本操作和数据结构

1：基本的数据结构如下：

struct dentry *dentry;/*include/dcache.h 目录项*/

struct inode *inode;/*include/fs.h 索引节点*/

struct super_block;/*include/fs.h 超级块*/

2：超级块的描述

struct super_block {
	struct list_head	s_list;		/* Keep this first 链表指针*/
	dev_t			s_dev;		/* search index; _not_ kdev_t 设备信息*/
	unsigned long		s_blocksize;    /* 块信息*/
	unsigned char		s_blocksize_bits;
	unsigned char		s_dirt;
	loff_t			s_maxbytes;	/* Max file size */
	struct file_system_type	*s_type;
	const struct super_operations	*s_op;  /* 对应的方法操作*/
	const struct dquot_operations	*dq_op;
	const struct quotactl_ops	*s_qcop;
	const struct export_operations *s_export_op;
	unsigned long		s_flags;
	unsigned long		s_magic;
	struct dentry		*s_root; /*根节点*/
	struct rw_semaphore	s_umount;
	struct mutex		s_lock;
	int			s_count;
	int			s_need_sync;
	atomic_t		s_active;
#ifdef CONFIG_SECURITY
	void                    *s_security;
#endif
	struct xattr_handler	**s_xattr;

	struct list_head	s_inodes;	/* all inodes */
	struct hlist_head	s_anon;		/* anonymous dentries for (nfs) exporting */
	struct list_head	s_files;
	/* s_dentry_lru and s_nr_dentry_unused are protected by dcache_lock */
	struct list_head	s_dentry_lru;	/* unused dentry lru */
	int			s_nr_dentry_unused;	/* # of dentry on lru */

	struct block_device	*s_bdev;              /*设备*/
	struct backing_dev_info *s_bdi;
	struct mtd_info		*s_mtd;
	struct list_head	s_instances;
	struct quota_info	s_dquot;	/* Diskquota specific options */

	int			s_frozen;
	wait_queue_head_t	s_wait_unfrozen;

	char s_id[32];				/* Informational name */

	void 			*s_fs_info;	/* Filesystem private info */
	fmode_t			s_mode;

	/*
	 * The next field is for VFS *only*. No filesystems have any business
	 * even looking at it. You had been warned.
	 */
	struct mutex s_vfs_rename_mutex;	/* Kludge */

	/* Granularity of c/m/atime in ns.
	   Cannot be worse than a second */
	u32		   s_time_gran;

	/*
	 * Filesystem subtype.  If non-empty the filesystem type field
	 * in /proc/mounts will be "type.subtype"
	 */
	char *s_subtype;

	/*
	 * Saved mount options for lazy filesystems using
	 * generic_show_options()
	 */
	char *s_options;
};

每个文件系统都有一个超级块，被挂载在超级块链表中。

从超级块结构体中认识到，超级块挂载inode以及file信息。

操作方法结果：

struct super_operations {
   	struct inode *(*alloc_inode)(struct super_block *sb);
	void (*destroy_inode)(struct inode *);


   	void (*dirty_inode) (struct inode *);
	int (*write_inode) (struct inode *, int);
	void (*drop_inode) (struct inode *);
	void (*delete_inode) (struct inode *);
	void (*put_super) (struct super_block *);
	void (*write_super) (struct super_block *);
	int (*sync_fs)(struct super_block *sb, int wait);
	int (*freeze_fs) (struct super_block *);
	int (*unfreeze_fs) (struct super_block *);
	int (*statfs) (struct dentry *, struct kstatfs *);
	int (*remount_fs) (struct super_block *, int *, char *);
	void (*clear_inode) (struct inode *);
	void (*umount_begin) (struct super_block *);


	int (*show_options)(struct seq_file *, struct vfsmount *);
	int (*show_stats)(struct seq_file *, struct vfsmount *);
#ifdef CONFIG_QUOTA
	ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
	ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
#endif
	int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
};

3：目录项

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 */
	/*
	 * 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 哈希表*/
	struct dentry *d_parent;	/* parent directory 关系*/
	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 */
};

dentry挂载在hashtable中,

struct dentry_operations {
	int (*d_revalidate)(struct dentry *, struct nameidata *);
	int (*d_hash) (struct dentry *, struct qstr *);
	int (*d_compare) (struct dentry *, struct qstr *, struct qstr *);
	int (*d_delete)(struct dentry *);
	void (*d_release)(struct dentry *);
	void (*d_iput)(struct dentry *, struct inode *);
	char *(*d_dname)(struct dentry *, char *, int);
};

挂载点本身也是dentry项,被挂载mount_hashtable中.