Direct disk block access in UNIX

if one were to write a program to check disk blocks in unix, could you make it FS independent and what do you need to do this?

i'm used to programming in c on unix but i've never done any low level hardware stuff like this, i could check the fsck source but i'd rather ask you guys

also i believe fsck checks the filesystem, not the blocks on the disk. i want to write a program that is FS independent and can for example check a FFS disk or an externally mounted NTFS disk in the same way

i don't know enough about hardware to get started on this project without some help, first of all, how do you check the sectors or blocks? do you have to force a read/write to them or can you check them without affecting the data? read test would be easy but how do you verify data? i guess the test will only fail if the read fails but what about writing?

also i'm thinking i can't run this from inside the OS so i plan to run it from a bootable cd, all i really need is the disk to show up in /dev so i can access the physical device for read/write operations

i know there probably already are tools like this but this is just for fun

http://git.kernel.org/?p=fs/ext2/e2fsprogs.git;a=blob;f=misc/badblocks.c;h=f7d67a77a343e16263e8aa2a632be155a66b4322;hb=HEAD