->permission() sanitizing: document API changes

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/porting

@@ -398,12 +398,16 @@ Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,
 so the i_size should not change when hole punching, even when puching the end of
 a file off.
 
---
-[mandatory]
-
 --
 [mandatory]
 	->get_sb() is gone.  Switch to use of ->mount().  Typically it's just
 a matter of switching from calling get_sb_... to mount_... and changing the
 function type.  If you were doing it manually, just switch from setting ->mnt_root
 to some pointer to returning that pointer.  On errors return ERR_PTR(...).
+
+--
+[mandatory]
+	->permission(), generic_permission() and ->check_acl() have lost flags
+argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.
+	generic_permission() has also lost the check_acl argument; if you want
+non-NULL to be used for that inode, put it into ->i_op->check_acl.