update documentation for the new truncate sequence
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index a7e9746..f9547a5 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -273,3 +273,21 @@
deliberate; as soon as struct block_device * is propagated in a reasonable
way by that code fixing will become trivial; until then nothing can be
done.
+
+[mandatory]
+
+ block truncatation on error exit from ->write_begin, and ->direct_IO
+moved from generic methods (block_write_begin, cont_write_begin,
+nobh_write_begin, blockdev_direct_IO*) to callers. Take a look at
+ext2_write_failed and callers for an example.
+
+[mandatory]
+
+ ->truncate is going away. The whole truncate sequence needs to be
+implemented in ->setattr, which is now mandatory for filesystems
+implementing on-disk size changes. Start with a copy of the old inode_setattr
+and vmtruncate, and the reorder the vmtruncate + foofs_vmtruncate sequence to
+be in order of zeroing blocks using block_truncate_page or similar helpers,
+size update and on finally on-disk truncation which should not fail.
+inode_change_ok now includes the size checks for ATTR_SIZE and must be called
+in the beginning of ->setattr unconditionally.