SI_BUFSZ
bufs = kmem_alloc(NSIBUF * SI_BUFSZ, KM_SLEEP);
bp->b_bufsize = bp->b_bcount = SI_BUFSZ;
bp->b_un.b_addr = bufs + (i * SI_BUFSZ);
kmem_free(bufs, NSIBUF * SI_BUFSZ);