update Documentation/filesystems/vfs.txt

-----------------------

This describes how the VFS can manipulate the superblock of your

filesystem. As of kernel 2.6.13, the following members are defined:

filesystem. As of kernel 2.6.22, the following members are defined:

struct super_operations {

        struct inode *(*alloc_inode)(struct super_block *sb);

        void (*clear_inode) (struct inode *);

        void (*umount_begin) (struct super_block *);

        void (*sync_inodes) (struct super_block *sb,

                                struct writeback_control *wbc);

        int (*show_options)(struct seq_file *, struct vfsmount *);

        ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);

  umount_begin: called when the VFS is unmounting a filesystem.

  sync_inodes: called when the VFS is writing out dirty data associated with

  	a superblock.

  show_options: called by the VFS to show mount options for /proc/<pid>/mounts.

  quota_read: called by the VFS to read from filesystem quota file.

-----------------------

This describes how the VFS can manipulate an inode in your

filesystem. As of kernel 2.6.13, the following members are defined:

filesystem. As of kernel 2.6.22, the following members are defined:

struct inode_operations {

	int (*create) (struct inode *,struct dentry *,int, struct nameidata *);

	ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);

	ssize_t (*listxattr) (struct dentry *, char *, size_t);

	int (*removexattr) (struct dentry *, const char *);

	void (*truncate_range)(struct inode *, loff_t, loff_t);

};

Again, all methods are called without any locks being held, unless

  removexattr: called by the VFS to remove an extended attribute from

  	a file. This method is called by removexattr(2) system call.

  truncate_range: a method provided by the underlying filesystem to truncate a

  	range of blocks , i.e. punch a hole somewhere in a file.

The Address Space Object

========================

-------------------------------

This describes how the VFS can manipulate mapping of a file to page cache in

your filesystem. As of kernel 2.6.16, the following members are defined:

your filesystem. As of kernel 2.6.22, the following members are defined:

struct address_space_operations {

	int (*writepage)(struct page *page, struct writeback_control *wbc);

			int);

	/* migrate the contents of a page to the specified target */

	int (*migratepage) (struct page *, struct page *);

	int (*launder_page) (struct page *);

};

  writepage: called by the VM to write a dirty page to backing store.

	transfer any private data across and update any references

        that it has to the page.

  launder_page: Called before freeing a page - it writes back the dirty page. To

  	prevent redirtying the page, it is kept locked during the whole

	operation.

The File Object

===============

----------------------

This describes how the VFS can manipulate an open file. As of kernel

2.6.17, the following members are defined:

2.6.22, the following members are defined:

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 *);

	int (*check_flags)(int);

	int (*dir_notify)(struct file *filp, unsigned long arg);

	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);

	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);

};

Again, all methods are called without any locks being held, unless