How to know the filesystem type on one block device?

[Magicloud Wang <magicloud.magiclouds@gmail.com>]

Dear,
	By filesystem type, I mean including swap.
	Mount it or `file` a dd image of it sure can tell me the filesystem. But 
these can not deal with swap, and too complax.
	Parted can tell this information of a partition, but can not deal with lvm. 
While `lvdisplay` can not tell.

	So, any idea?

Thanks.