vfs: clean up documentation

				struct file *, unsigned open_flag,

				umode_t create_mode, int *opened);

	int (*tmpfile) (struct inode *, struct dentry *, umode_t);

	int (*dentry_open)(struct dentry *, struct file *, const struct cred *);

locking rules:

	all may block

update_time:	no

atomic_open:	yes

tmpfile:	no

dentry_open:	no

	Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on

victim.

	int (*atomic_open)(struct inode *, struct dentry *, struct file *,

			unsigned open_flag, umode_t create_mode, int *opened);

	int (*tmpfile) (struct inode *, struct dentry *, umode_t);

	int (*dentry_open)(struct dentry *, struct file *, const struct cred *);

};

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

  	but instead uses bmap to find out where the blocks in the file

  	are and uses those addresses directly.

  dentry_open: *WARNING: probably going away soon, do not use!* This is an

	alternative to f_op->open(), the difference is that this method may open

	a file not necessarily originating from the same filesystem as the one

	i_op->open() was called on.  It may be useful for stacking filesystems

	which want to allow native I/O directly on underlying files.

  invalidatepage: If a page has PagePrivate set, then invalidatepage

        will be called when part or all of the page is to be removed

	from the address space.  This generally corresponds to either a

	at the end of the buffer, and returns a pointer to the first char.

	dynamic_dname() helper function is provided to take care of this.

	Example :

	static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen)

	{

		return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",

				dentry->d_inode->i_ino);

	}

  d_automount: called when an automount dentry is to be traversed (optional).

	This should create a new VFS mount record and return the record to the

	caller.  The caller is supplied with a path parameter giving the

	This method is never called with both non-NULL inode and non-zero flags.

Example :

static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen)

{

	return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",

				dentry->d_inode->i_ino);

}

Each dentry has a pointer to its parent dentry, as well as a hash list

of child dentries. Child dentries are basically like files in a

directory.