[Yaffs] yaffs checkpoint block info problem

yaffs_CheckpointFindNextCheckpointBlock :

dev->readChunkWithTagsFromNAND(dev,realignedChunk,NULL,&tags);
if(tags.sequenceNumber == YAFFS_SEQUENCE_CHECKPOINT_DATA)
{
......
}

If this block is "bad block", the tags seq value may equal to
YAFFS_SEQUENCE_CHECKPOINT_DATA , so yaffs stop read checkpoint data
from the real
checkpoint block.
Any tips?