For the first phase of growth, the online resizing code starts by briefly locking the superblock and increasing the total number of filesystem blocks to the end of the last group. All of the blocks beyond the end of the filesystem are already marked as ``in use'' by the block bitmap for that group, so they must be cleared. This is accomplished by the same mechanism that is used when deleting a file - ext3_free_blocks() and can be done without locking the whole filesystem. The online resizer simply pretends that it is deleting a file that had allocated all of the blocks at the end of the filesystem, and ext3_free_blocks() handles all of the bitmap and free block count updates properly.