Unsigned long is not always the same size as a pointer, namely on 32 bit systems with 64 bit address space. Ptrdiff_t is the same size as a pointer in all configurations. By using ptrdiff_t we can mitigate the warning messages on these configurations. There should be no side effects of this patch. ObligatoryDisclaimer: Please accept my condolences regarding Outlook's handling of patches attachments. This attached patch is against current scsi-misc-2.6 Signed-off-by: Mark Salyzyn