1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index 0eeb3954dea3..6b96773e27cb 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -411,3 +411,13 @@ to some pointer to returning that pointer.  On errors return ERR_PTR(...).
 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.
+
+--
+[mandatory]
+        If you implement your own ->llseek() you must handle SEEK_HOLE and
+SEEK_DATA.  You can hanle this by returning -EINVAL, but it would be nicer to
+support it in some way.  The generic handler assumes that the entire file is
+data and there is a virtual hole at the end of the file.  So if the provided
+offset is less than i_size and SEEK_DATA is specified, return the same offset.
+If the above is true for the offset and you are given SEEK_HOLE, return the end
+of the file.  If the offset is i_size or greater return -ENXIO in either case.