BITMAP_LAST_BYTE_MASK
mask &= BITMAP_LAST_BYTE_MASK(pos + len);
*kaddr |= BITMAP_LAST_BYTE_MASK(pos + len);
mask &= BITMAP_LAST_BYTE_MASK(pos + len);
*kaddr &= ~BITMAP_LAST_BYTE_MASK(pos + len);
mask_to_set &= BITMAP_LAST_BYTE_MASK(size);