Getting the sector number

Hi All,

I am trying to get whether a request has come for the very first sector or
not. The logic for that is.

irpSp->Parameters.Write.ByteOffset.QuadPart += (Starting offset of
Partition/Volume);

firstSectorOfRequest = (ULONG)(irpSp->Parameters.Write.ByteOffset.QuadPart

> (n where 2 power n = No of bytes in a
sector);

If firstSectorOfRequest is less than number of bytes in a sector then it
means the request is for the very first sector
Now my problem is how can I get the starting offset of the partition i am
working on, and the number of bytes in a sector of the drive.

Thanks and Regards,
Lalit