NVH_HSIZE
#define NVH_SIZE(nvh) (NVH_HSIZE(nvh) + roundup2(NVH_DSIZE(nvh), 8))
if (size < NVH_HSIZE(nvh)) {
roundup2(dsize, 8) > size - NVH_HSIZE(nvh)) {
if (ebuf_add_tail(nv->nv_ebuf, nvh, NVH_HSIZE(nvh)) == -1) {
#define NVH_DATA(nvh) ((unsigned char *)nvh + NVH_HSIZE(nvh))