[Yaffs] nandsim and mkyaffs2image problem

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Hi:
I use  mkyaffs2image to make the img,and use  the nandsim tool  to mount  
it on fake /dev/mtdblock/0,
but the file is lost.Is there some one comfront  the same problem?
  Here is my step :
	mkyaffs2image  fsdir yaffs.img
	dd if=yaffs.img of=/dev/mtdblock/0
	mount -t yaffs  /dev/mtdblock/0 /mnt/

Regards.