ext2: Handle fiemap on empty files to prevent EINVAL

Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
then result in an -EINVAL error, even for valid queries on empty files.

Link: linux-test-project/ltp#1246
Signed-off-by: Wei Gao <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: coolgw

fs/ext2/inode.c

@@ -895,9 +895,19 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		u64 start, u64 len)
 {
 	int ret;
+	loff_t i_size;
 
 	inode_lock(inode);
-	len = min_t(u64, len, i_size_read(inode));
+	i_size = i_size_read(inode);
+	/*
+	 * iomap_fiemap() returns EINVAL for 0 length. Make sure we don't trim
+	 * length to 0 but still trim the range as much as possible since
+	 * ext2_get_blocks() iterates unmapped space block by block which is
+	 * slow.
+	 */
+	if (i_size == 0)
+		i_size = 1;
+	len = min_t(u64, len, i_size);
 	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
 	inode_unlock(inode);