1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index fa2db081505e..4006483c275f 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -471,3 +471,12 @@ in your dentry operations instead.
 [mandatory]
         f_dentry is gone; use f_path.dentry, or, better yet, see if you can avoid
         it entirely.
+--
+[mandatory]
+        never call ->read() and ->write() directly; use __vfs_{read,write} or
+        wrappers; instead of checking for ->write or ->read being NULL, look for
+        FMODE_CAN_{WRITE,READ} in file->f_mode.
+--
+[mandatory]
+        do _not_ use new_sync_{read,write} for ->read/->write; leave it NULL
+        instead.