kmem_cache_init ()

Hi,
     I was unable to understand the logic of the following sanity checks in
slab.c/kmem_cache_init ().

if (kmem_cache_diff(c_firstp,c_magic) != kmem_slab_diff(s_nextp,s_magic) ||
kmem_cache_diff(c_firstp,c_inuse) != kmem_slab_diff(s_nextp,s_inuse) ||
kmem_cache_offset(c_lastp) - ((unsigned long) kmem_slab_end((kmem_cache_t
*)NULL)) != kmem_slab_offset(s_prevp) || kmem_cache_diff(c_lastp,c_firstp) !=
kmem_slab_diff(s_prevp,s_nextp)) {
     /** offsets to the magic are incorrect **/
}

can someone throw some light behind the above logic

Thanks
Amol