update Documentation/filesystems/ regarding the follow_link/put_link changes

--

[mandatory]

	->aio_read/->aio_write are gone.  Use ->read_iter/->write_iter.

---

[recommended]

	for embedded ("fast") symlinks just set inode->i_link to wherever the

	symlink body is and use simple_follow_link() as ->follow_link().

--

[mandatory]

	calling conventions for ->follow_link() have changed.  Instead of returning

	cookie and using nd_set_link() to store the body to traverse, we return

	the body to traverse and store the cookie using explicit void ** argument.

	nameidata isn't passed at all - nd_jump_link() doesn't need it and

	nd_[gs]et_link() is gone.

--

[mandatory]

	calling conventions for ->put_link() have changed.  It gets inode instead of

	dentry,  it does not get nameidata at all and it gets called only when cookie

	is non-NULL.  Note that link body isn't available anymore, so if you need it,

	store it as cookie.

  follow_link: called by the VFS to follow a symbolic link to the

	inode it points to.  Only required if you want to support

	symbolic links.  This method returns a void pointer cookie

	that is passed to put_link().

	symbolic links.  This method returns the symlink body

	to traverse (and possibly resets the current position with

	nd_jump_link()).  If the body won't go away until the inode

	is gone, nothing else is needed; if it needs to be otherwise

	pinned, the data needed to release whatever we'd grabbed

	is to be stored in void * variable passed by address to

	follow_link() instance.

  put_link: called by the VFS to release resources allocated by

  	follow_link().  The cookie returned by follow_link() is passed

  	to this method as the last parameter.  It is used by

  	filesystems such as NFS where page cache is not stable

  	(i.e. page that was installed when the symbolic link walk

  	started might not be in the page cache at the end of the

  	walk).

	follow_link().  The cookie stored by follow_link() is passed

	to this method as the last parameter; only called when

	cookie isn't NULL.

  permission: called by the VFS to check for access rights on a POSIX-like

  	filesystem.