M_EXTWR
MEXTADD(m, mcl, MYX_RXBIG_SIZE, M_EXTWR, MEXTFREE_POOL, myx_mcl_pool);
MEXTADD(m, block + off, PAGE_SIZE, M_EXTWR,
to->m_flags = (to->m_flags & (M_EXT | M_EXTWR));
m->m_flags &= (M_EXT|M_PKTHDR|M_EOR|M_EXTWR|M_ZEROIZE);
MEXTADD(m, buf, pp->pr_size, M_EXTWR, MEXTFREE_POOL, pp);
n->m_flags |= o->m_flags & (M_EXT|M_EXTWR);
m->m_flags &= ~(M_EXT|M_EXTWR);
m->m_flags |= m0->m_flags & (M_EXT|M_EXTWR);
m0->m_flags &= ~(M_EXT|M_EXTWR); /* cluster is gone */
MEXTADD(m, pkt, sizeof(*pkt), M_EXTWR,
(m)->m_flags |= M_EXT | (mflags & M_EXTWR); \
(to)->m_flags = ((to)->m_flags & (M_EXT | M_EXTWR)); \
(((m)->m_flags & M_EXTWR) == 0 || MCLISREFERENCED(m)))