文件系统内部结构解析-优快云博客

§Filesystems are a collection of files that are stored in the system in some way

§So many file system!

Disk file:

§Boot block

§Super block

−Magic number

−Revision

−Mount count and Maximum Mount count

−Block Group number

−Block size

−Block per Group

−Free Blocks //need sync to disk

−Free inodes //need sync to disk

−First inode ‘/’

§Index(GDT)

−Block bitmap

−inode bitmap

−Inode table

VFS:

§abstraction layer on top of a more concrete file system

−Sys_read, sys_write, sys_open, …

§interface

−File_operations

−Dentry

−File name (sub directory), parent directory, …

−File tree

−6 list_head:

−d_vfsmnt

−d_hash dentry_hashtable

−d_lru dentry_unused

−d_child patent->d_subdirs

−d_subdirs sub->dentry

−d_alias

−Inode

−Files information

−File type, atime, mtime, link numer, length, ACL, location

Dentry:

§struct dentry { /*include/linux/dcache.h*/

§ atomic_t d_count;

§ unsigned int d_flags;

§ struct inode * d_inode; /* Where the name belongs to - NULL is negative */

§ struct dentry * d_parent; /* parent directory */

§ struct list_head d_hash; /* lookup hash list */

§ struct list_head d_lru; /* d_count = 0 LRU list */

§ struct list_head d_child; /* child of parent list */

§ struct list_head d_subdirs; /* our children */

§ struct list_head d_alias; /* inode alias list */

§ int d_mounted;

§ struct qstr d_name;

§ unsigned long d_time; /* used by d_revalidate */

§ struct dentry_operations *d_op;

§ struct super_block * d_sb; /* The root of the dentry tree */

§ unsigned long d_vfs_flags;

§ void * d_fsdata; /* fs-specific data */

§ unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */

§};

Super block:

2 struct super_block {
3         struct list_head s_list; /* Keep this first */
4         dev_t s_dev;                                 /* search index; _not_ kdev_t */
5         unsigned long s_blocksize;                     //数据块大小
6         unsigned char s_blocksize_bits;             //块大小占用的位数
7         unsigned char s_dirt;                         //脏位，如果该位置位，说明超级块被修改
8         unsigned long long s_maxbytes;                //单个文件最大体积
9         struct file_system_type *s_type;             //文件系统结构
10         struct super_operations *s_op;                 //超级块支持的操作
11         struct dquot_operations *dq_op;             //
12         struct quotactl_ops *s_qcop;                 //用户配额限制
13         struct export_operations *s_export_op;        //
14
15         unsigned longs_flags;
16         unsigned long s_magic;                         //区块的magic数
17         struct dentry *s_root;                         //根目录
18         struct rw_semaphore s_umount;                 //
19         struct mutex s_lock;                         //
20         int s_count;                                 //

21         int s_syncing;                                 //
22         int s_need_sync_fs;                         //
23         atomic_t s_active;                             //是否活动
24         void *s_security;                             //
25         struct xattr_handler **s_xattr;                //
26

27         struct list_head s_inodes;                    //所有inode
28         struct list_head s_dirty;                     //脏inode
29         struct list_head s_io;                        //用于写回的缓存
30         struct hlist_head s_anon;                     //nfs匿名入口
31         struct list_head s_files;                    //文件链表头
32
33         struct block_device *s_bdev;
34         struct list_head s_instances;
35         struct quota_info s_dquot;                     //配额定制选项
36
37         int s_frozen;
38         wait_queue_head_t s_wait_unfrozen;
39
40         char s_id[32];                                //名字
41
……

Lookup file:

§Path_init

−initialize nameidata (struct)

§Path_walk

−Calculate name hash(H), hast_table(H),

−i_hash_next, i_hash_prev

−Cached_lookup() hit dentry cache

−real_lookup() miss dentry cache

−d_alloc()

−Ext2_lookup/ext3_lookup/……

−Xxx_find_entry()

−iget()