f2fs: record node block allocation in dnode_of_data

This patch introduces recording node block allocation in dnode_of_data.
This information helps to figure out whether any node block is allocated during
specific file operations.

Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index cf0c9dd..a7a9a05 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -226,6 +226,7 @@
 	addr_array = blkaddr_in_node(rn);
 	addr_array[ofs_in_node] = cpu_to_le32(dn->data_blkaddr);
 	set_page_dirty(node_page);
+	dn->node_changed = true;
 }
 
 int reserve_new_block(struct dnode_of_data *dn)