虚拟文件系统（VFS)

To register and unregister a filesystem, use the following API functions:

   #include <linux/fs.h>

   extern int register_filesystem(struct file_system_type *);

   extern int unregister_filesystem(struct file_system_type *);

       int fs_flags; int (*get_sb) (struct file_system_type *, int, const char *, void *, struct vfsmount *);

        struct module *owner;

        struct file_system_type * next;

        struct list_head fs_supers;

 struct lock_class_key s_lock_key;

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 *);

       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 (*readv) (struct file *, const struct iovec *, unsigned long, loff_t *);

ssize_t (*writev) (struct file *, const struct iovec *, unsigned long, loff_t *);

ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t, void *);

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 (*flock) (struct file *, int, struct file_lock *);

       ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned int);

 ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned int); };