dmc_header
sizeof(struct dmc_header) + DMCMTU,
rp->cc = DMCMTU + sizeof (struct dmc_header);
struct dmc_header *dh;
len = (arg & DMC_CCOUNT) - sizeof (struct dmc_header);
dh = (struct dmc_header *)ifrw->ifrw_addr;
m_adj(m, sizeof(struct dmc_header));
struct dmc_header *dh;
dh = (struct dmc_header *)dst->sa_data;
M_PREPEND(m, sizeof(struct dmc_header), M_DONTWAIT);
dh = mtod(m, struct dmc_header *);