Hi Linus, On 22 Sep 2014, at 16:33, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Sep 22, 2014 at 8:29 AM, Anton Altaparmakov <aia21@xxxxxxxxx> wrote: >> >> You could do "block & ~(sector_t)(size - 1)" instead of "(sector_t)index << sizebits" if you prefer but not sure that is an improvement! > > No, it would be even worse. Something like > > block & ~(sector_t)((size >> 9) - 1) > > because block is the sector number (ie 512-byte) and size is in bytes. Oops, sorry. But I think you got it wrong, too as you are ignoring the PAGE_SIZE - as was I but it is what we need to align to in addition to the problem of "size" being in bytes. So I think the correct mask is actually based on sizebits which reflects the number of blocks per page thus: block & ~(sector_t)((1 << sizebits) - 1) In any case the shift is the lesser evil I think as it is at least obviously correct whilst getting the right mask has taken us a few iterations of correcting each other! (-: PS. Thank you for taking my patch and correcting the misleading description! Best regards, Anton > Linus -- Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @) University of Cambridge Information Services, Roger Needham Building 7 JJ Thomson Avenue, Cambridge, CB3 0RB, UK -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
