ext4: use FIEMAP_EXTENT_LAST flag for last extent in fiemap

Currently we are not marking the extent as the last one
(FIEMAP_EXTENT_LAST) if there is a hole at the end of the file. This is
because we just do not check for it right now and continue searching for
next extent. But at the point we hit the hole at the end of the file, it
is too late.

This commit adds check for the allocated block in subsequent extent and
if there is no more extents (block = EXT_MAX_BLOCKS) just flag the
current one as the last one.

This behaviour has been spotted unintentionally by 252 xfstest, when the
test hangs out, because of wrong loop condition. However on other
filesystems (like xfs) it will exit anyway, because we notice the last
extent flag and exit.

With this patch xfstest 252 does not hang anymore, ext4 fiemap
implementation still reports bad extent type in some cases, however
this seems to be different issue.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4_extents.h

@@ -125,7 +125,7 @@ struct ext4_ext_path {
  * positive retcode - signal for ext4_ext_walk_space(), see below
  * callback must return valid extent (passed or newly created)
  */
-typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
+typedef int (*ext_prepare_callback)(struct inode *, ext4_lblk_t,
 					struct ext4_ext_cache *,
 					struct ext4_extent *, void *);
 

fs/ext4/extents.c

@@ -1958,7 +1958,7 @@ static int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t block,
 			err = -EIO;
 			break;
 		}
-		err = func(inode, path, &cbex, ex, cbdata);
+		err = func(inode, next, &cbex, ex, cbdata);
 		ext4_ext_drop_refs(path);
 
 		if (err < 0)
@@ -3914,14 +3914,13 @@ int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
 /*
  * Callback function called for each extent to gather FIEMAP information.
  */
-static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
+static int ext4_ext_fiemap_cb(struct inode *inode, ext4_lblk_t next,
 		       struct ext4_ext_cache *newex, struct ext4_extent *ex,
 		       void *data)
 {
 	__u64	logical;
 	__u64	physical;
 	__u64	length;
-	loff_t	size;
 	__u32	flags = 0;
 	int		ret = 0;
 	struct fiemap_extent_info *fieinfo = data;
@@ -4103,8 +4102,7 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
 	if (ex && ext4_ext_is_uninitialized(ex))
 		flags |= FIEMAP_EXTENT_UNWRITTEN;
 
-	size = i_size_read(inode);
-	if (logical + length >= size)
+	if (next == EXT_MAX_BLOCKS)
 		flags |= FIEMAP_EXTENT_LAST;
 
 	ret = fiemap_fill_next_extent(fieinfo, logical, physical,