【文件系统】文件系统中的数据结构

目录

 

0.参考

1.文件系统的主要数据结构

2.超级块及其操作函数

3.inode及其操作函数

4.目录项数据结构定义及操作函数

5.文件结构体的定义及文件的操作函数

---

0.参考

推荐老师及视频：
西安邮电大学研究生导师陈莉君老师《高级操作系统》,可以上B站搜索教学视频,为防止被删,可以缓存.

推荐ups主:善不外来名不虚传

清华大学《高级操作系统》视频,陈渝老师在2020年2-5月录了这个视频

推荐书目：
《LINUX内核设计与实现》第二版,第三版


推荐链接：
内容摘选自
https://www.cnblogs.com/smartjourneys/p/7258226.html--文件系统1
https://www.cnblogs.com/smartjourneys/p/7260911.html--文件系统2
https://blog.youkuaiyun.com/yunsongice/article/details/5683859
https://blog.youkuaiyun.com/GerryLee93/article/details/106476030 --哈希链表

（以上感恩）

1.文件系统的主要数据结构

文件系统本身的数据结构
Linux内核采用VFS(Virtual Filesystem Switch)框架
每个文件系统都需要在VFS中注册，即填充一个struct file_system_type结构
此结构描述的是文件系统的名称以及一个指向对应VFS超级块读取例程的地址等信息

文件系统宏观上的两个数据结构：
(1)struct file_system_type
(2)struct vfsmount


文件系统的四个主要对象对应的数据结构
(1)超级块对象   存放系统中已安装文件系统的信息
(2)索引节点对象 存放关于具体文件的一般信息
(3)目录项对象   存放目录项与对应文件进行链接的信息
(4)文件对象     存放打开文件与进程之间进行交互的有关信息



文件系统宏观上的两个数据结构：
(1)
struct file_system_type {

	const char *name;
	int fs_flags;
	struct super_block *(*read_super) (struct super_block *, void *, int);//ext2_read_super读取超级块，一般是第一个块
	struct module *owner;
	struct file_system_type * next;
	struct list_head fs_supers;

};

5.8.13中这么定义：
struct file_system_type {
	const char *name;
	int fs_flags;
#define FS_REQUIRES_DEV		1 
#define FS_BINARY_MOUNTDATA	2
#define FS_HAS_SUBTYPE		4
#define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
#define FS_DISALLOW_NOTIFY_PERM	16	/* Disable fanotify permission events */
#define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
	int (*init_fs_context)(struct fs_context *);
	const struct fs_parameter_spec *parameters;
	struct dentry *(*mount) (struct file_system_type *, int,const char *, void *);
	void (*kill_sb) (struct super_block *);
	struct module *owner;
	struct file_system_type * next;
	struct hlist_head fs_supers;

	struct lock_class_key s_lock_key;
	struct lock_class_key s_umount_key;
	struct lock_class_key s_vfs_rename_key;
	struct lock_class_key s_writers_key[SB_FREEZE_LEVELS];

	struct lock_class_key i_lock_key;
	struct lock_class_key i_mutex_key;
	struct lock_class_key i_mutex_dir_key;
};

这相当于一个文件系统的类,比如会有各种文件系统,比如说ext2文件系统,xfs文件系统,drm文件系统
等系统.这样在去实例化的时候,相当于定义了一个类的一个对象,每一个文件系统都是一个对象,对象
与对象之间通过指针串起来.这里的链表是单向链表,可能是不经常添加或者删除文件系统吧.

(2)还有一个与文件系统本身相关的数据结构：struct vfsmout，在5.8.13中是这么定义的：
struct vfsmount {
	struct dentry *mnt_root;	/* root of the mounted tree */
	struct super_block *mnt_sb;	/* pointer to superblock */
	int mnt_flags;
} __randomize_layout;


D:\005-代码\001-开源项目源码\004-内核源码\linux-2.6.11.10\include\linux\mount.h中是这么定义的：
struct vfsmount
{
	struct list_head mnt_hash;
	struct vfsmount *mnt_parent;	/* fs we are mounted on */
	struct dentry *mnt_mountpoint;	/* dentry of mountpoint */
	struct dentry *mnt_root;	/* root of the mounted tree */
	struct super_block *mnt_sb;	/* pointer to superblock */
	struct list_head mnt_mounts;	/* list of children, anchored here */
	struct list_head mnt_child;	/* and going through their mnt_child */
	atomic_t mnt_count;
	int mnt_flags;
	int mnt_expiry_mark;		/* true if marked for expiry */
	char *mnt_devname;		/* Name of device e.g. /dev/dsk/hda1 */
	struct list_head mnt_list;
	struct list_head mnt_fslink;	/* link in fs-specific expiry list */
	struct namespace *mnt_namespace; /* containing namespace */
};



每个文件系统都有一个全局file_system_type类型的全局变量，例如：ext2_fs_type代表ext2文件系统
mount的时候会调用read_super.

 

 

2.超级块及其操作函数

超级块用来描述整个文件系统的信息
每个具体的文件系统都有自己的超级块
VFS超级块是各种文件系统在安装时建立的，并在卸载时被自动删除，其数据结构是super_block
所有超级块对象都以双向循环链表的形式链接在一起

super_block的数据结构,摘自5.8.13版本的内核
D:\005-代码\001-开源项目源码\004-内核源码\linux-5.8.13\linux-5.8.13\include\linux\fs.h
struct super_block {
	struct list_head	s_list;		/* Keep this first */
	dev_t			s_dev;		/* search index; _not_ kdev_t */
	unsigned char		s_blocksize_bits;
	unsigned long		s_blocksize;
	loff_t			s_maxbytes;	/* Max file size */
	struct file_system_type	*s_type;
	const struct super_operations	*s_op;
	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_iflags;	/* internal SB_I_* flags */
	unsigned long		s_magic;
	struct dentry		*s_root;
	struct rw_semaphore	s_umount;
	int			s_count;
	atomic_t		s_active;
#ifdef CONFIG_SECURITY
	void                    *s_security;
#endif
	const struct xattr_handler **s_xattr;
#ifdef CONFIG_FS_ENCRYPTION
	const struct fscrypt_operations	*s_cop;
	struct key		*s_master_keys; /* master crypto keys in use */
#endif
#ifdef CONFIG_FS_VERITY
	const struct fsverity_operations *s_vop;
#endif
	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
	struct block_device	*s_bdev;
	struct backing_dev_info *s_bdi;
	struct mtd_info		*s_mtd;
	struct hlist_node	s_instances;
	unsigned int		s_quota_types;	/* Bitmask of supported quota types */
	struct quota_info	s_dquot;	/* Diskquota specific options */

	struct sb_writers	s_writers;

	/*
	 * Keep s_fs_info, s_time_gran, s_fsnotify_mask, and
	 * s_fsnotify_marks together for cache efficiency. They are frequently
	 * accessed and rarely modified.
	 */
	void			*s_fs_info;	/* Filesystem private info */

	/* Granularity of c/m/atime in ns (cannot be worse than a second) */
	u32			s_time_gran;
	/* Time limits for c/m/atime in seconds */
	time64_t		   s_time_min;
	time64_t		   s_time_max;
#ifdef CONFIG_FSNOTIFY
	__u32			s_fsnotify_mask;
	struct fsnotify_mark_connector __rcu	*s_fsnotify_marks;
#endif

	char			s_id[32];	/* Informational name */
	uuid_t			s_uuid;		/* UUID */

	unsigned int		s_max_links;
	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 */

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

	const struct dentry_operations *s_d_op; /* default d_op for dentries */

	/*
	 * Saved pool identifier for cleancache (-1 means none)
	 */
	int cleancache_poolid;

	struct shrinker s_shrink;	/* per-sb shrinker handle */

	/* Number of inodes with nlink == 0 but still referenced */
	atomic_long_t s_remove_count;

	/* Pending fsnotify inode refs */
	atomic_long_t s_fsnotify_inode_refs;

	/* Being remounted read-only */
	int s_readonly_remount;

	/* per-sb errseq_t for reporting writeback errors via syncfs */
	errseq_t s_wb_err;

	/* AIO completions deferred from interrupt context */
	struct workqueue_struct *s_dio_done_wq;
	struct hlist_head s_pins;

	/*
	 * Owning user namespace and default context in which to
	 * interpret filesystem uids, gids, quotas, device nodes,
	 * xattrs and security labels.
	 */
	struct user_namespace *s_user_ns;

	/*
	 * The list_lru structure is essentially just a pointer to a table
	 * of per-node lru lists, each of which has its own spinlock.
	 * There is no need to put them into separate cachelines.
	 */
	struct list_lru		s_dentry_lru;
	struct list_lru		s_inode_lru;
	struct rcu_head		rcu;
	struct work_struct	destroy_work;

	struct mutex		s_sync_lock;	/* sync serialisation lock */

	/*
	 * Indicates how deep in a filesystem stack this SB is
	 */
	int s_stack_depth;

	/* s_inode_list_lock protects s_inodes */
	spinlock_t		s_inode_list_lock ____cacheline_aligned_in_smp;
	struct list_head	s_inodes;	/* all inodes */

	spinlock_t		s_inode_wblist_lock;
	struct list_head	s_inodes_wb;	/* writeback inodes */
} __randomize_layout;

 

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

   	void (*dirty_inode) (struct inode *, int flags);
	int (*write_inode) (struct inode *, struct writeback_control *wbc);
	int (*drop_inode) (struct inode *);
	void (*evict_inode) (struct inode *);
	void (*put_super) (struct super_block *);
	int (*sync_fs)(struct super_block *sb, int wait);
	int (*freeze_super) (struct super_block *);
	int (*freeze_fs) (struct super_block *);
	int (*thaw_super) (struct super_block *);
	int (*unfreeze_fs) (struct super_block *);
	int (*statfs) (struct dentry *, struct kstatfs *);
	int (*remount_fs) (struct super_block *, int *, char *);
	void (*umount_begin) (struct super_block *);

	int (*show_options)(struct seq_file *, struct dentry *);
	int (*show_devname)(struct seq_file *, struct dentry *);
	int (*show_path)(struct seq_file *, struct dentry *);
	int (*show_stats)(struct seq_file *, struct dentry *);
#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);
	struct dquot **(*get_dquots)(struct inode *);
#endif
	int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
	long (*nr_cached_objects)(struct super_block *,
				  struct shrink_control *);
	long (*free_cached_objects)(struct super_block *,
				    struct shrink_control *);
};

 

 

3.inode及其操作函数

 

struct inode_operations {
	struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
	const char * (*get_link) (struct dentry *, struct inode *, struct delayed_call *);
	int (*permission) (struct inode *, int);
	struct posix_acl * (*get_acl)(struct inode *, int);

	int (*readlink) (struct dentry *, char __user *,int);

	int (*create) (struct inode *,struct dentry *, umode_t, bool);
	int (*link) (struct dentry *,struct inode *,struct dentry *);
	int (*unlink) (struct inode *,struct dentry *);
	int (*symlink) (struct inode *,struct dentry *,const char *);
	int (*mkdir) (struct inode *,struct dentry *,umode_t);
	int (*rmdir) (struct inode *,struct dentry *);
	int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
	int (*rename) (struct inode *, struct dentry *,
			struct inode *, struct dentry *, unsigned int);
	int (*setattr) (struct dentry *, struct iattr *);
	int (*getattr) (const struct path *, struct kstat *, u32, unsigned int);
	ssize_t (*listxattr) (struct dentry *, char *, size_t);
	int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
		      u64 len);
	int (*update_time)(struct inode *, struct timespec64 *, int);
	int (*atomic_open)(struct inode *, struct dentry *,
			   struct file *, unsigned open_flag,
			   umode_t create_mode);
	int (*tmpfile) (struct inode *, struct dentry *, umode_t);
	int (*set_acl)(struct inode *, struct posix_acl *, int);
} ____cacheline_aligned;

 

 

 

4.目录项数据结构定义及操作函数

 

 

5.文件结构体的定义及文件的操作函数

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 (*read_iter) (struct kiocb *, struct iov_iter *);
	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
	int (*iopoll)(struct kiocb *kiocb, bool spin);
	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);
	loff_t (*remap_file_range)(struct file *file_in, loff_t pos_in,
				   struct file *file_out, loff_t pos_out,
				   loff_t len, unsigned int remap_flags);
	int (*fadvise)(struct file *, loff_t, loff_t, int);
} __randomize_layout;