Btrfs: Add mount option to enforce a max extent size

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 2785641..7213012 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -569,6 +569,7 @@
 	fs_info->extent_root = extent_root;
 	fs_info->sb = sb;
 	fs_info->mount_opt = 0;
+	fs_info->max_extent = (u64)-1;
 	fs_info->btree_inode = new_inode(sb);
 	fs_info->btree_inode->i_ino = 1;
 	fs_info->btree_inode->i_nlink = 1;