今天在解决工作问题的同时也扩展我的知识面，有一种想深入研究文件系统的冲动，初略的研究了一下。
虚拟文件系统：VFS, virtual fiel system.
struct super_block { struct list_head s_list; //维护super_blocks全局变量的成员 dev_t s_dev; unsigned long s_blocksize; unsigned long s_old_blocksize; unsigned char s_blocksize_bits; unsigned char s_dirt; unsigned long long s_maxbytes; struct file_system_type *s_type; struct super_operations *s_op; struct dquot_operations *dq_op; struct quotactl_ops *s_qcop; struct export_operations *s_export_op; unsigned long s_flags; unsigned long s_magic; struct dentry *s_root; struct rw_semaphore s_umount; struct semaphore s_lock; int s_count; int s_syncing; int s_need_sync_fs; atomic_t s_active; void *s_security; struct xattr_handler **s_xattr;
struct list_head s_inodes; struct list_head s_dirty; struct list_head s_io; struct hlist_head s_anon; struct list_head s_files;
struct block_device *s_bdev; struct list_head s_instances; //维护特定文件系统全局变量的成员 struct quota_info s_dquot;
int s_frozen; wait_queue_head_t s_wait_unfrozen;
char s_id[32];
void *s_fs_info;
struct semaphore s_vfs_rename_sem;
u32 s_time_gran;};
super_block存在于两个链表中,一个是系统所有super_block的链表, 一个是对于特定的文件系统的super_block链表. 前者是被维护在一个全局变量super_blocks中，这个全局变量定义在文件fs/super.c。后者也是被维护在一个全局变量file_systems中，它被定义在文件fs/filesystems.c中。下图给予形象的展示：
所有的super_block都存在于 super-blocks 链表中: /------------/ /--------->|super_blocks|<--- .......... ---------------------/ | /------------/ | | | | super_block super_block super_block | | +-----------+ +-----------+ +-----------+ | /----->| s_list |<--------->| s_list |<--------->| s_list |<---/ +-----------+ +-----------+ +-----------+ | s_inodes | | s_inodes | | s_inodes | +-----------+ +-----------+ +-----------+ | s_files | | s_files | | s_files | +-----------+ +-----------+ +-----------+ | s_dirty | | s_dirty | | s_dirty | +-----------+ +-----------+ +-----------+ | s_op | | s_op | | s_op | +-----------+ +-----------+ +-----------+ | s_fs_info| | s_fs_info| | s_fs_info| +-----------+ +-----------+ +-----------+ | | | | | |
对于特定的文件系统, 该文件系统的所有的super block 都存在于file_sytem_type中的fs_supers链表中.而所有的文件系统,都存在于file_systems链表中.这是通过调用register_filesystem接口来注册文件系统的.int register_filesystem(struct file_system_type * fs)
file_system_type file_system_type /--->+-------------+ /--->+-------------+ | | name | | | name | /--------------/ | +-------------+ | +-------------+ /------/| file_systems |----/ | next |----/ | next |---->| NULL |/--------------/ +-------------+ +-------------+ /------/ | get_sb | | get_sb | +-------------+ +-------------+ | kill_sb | | kill_sb | +-------------+ +-------------+ /---------------->| fs_supers |<---/ | fs_supers | | +-------------+ | +-------------+ | | | | | | | /------------->+-------------+ | +-------------+ | | // | | | || /------------.............------/ | | |/--------------------/ | | | | | | | | super_block | super_block | super_block | | | +-------------+ | +-------------+ | +-------------+ | | /---| s_type | /----| s_type | /---| s_type | | | +-------------+ +-------------+ +-------------+ | /----->| s_instances |<------>| s_instances |<---->| s_instances |---/ +-------------+ +-------------+ +-------------+ | | | | | | +-------------+ +-------------+ +-------------+ | | | | | | +-------------+ +-------------+ +-------------+ | | | | | |
