m_prepend
_mm = m_prepend(_mm, _mplen, __mhow); \
struct mbuf *m_prepend(struct mbuf *, int, int);
bp = m_prepend(bp, cp, 2, 0);
bp = m_prepend(bp, &lh, sizeof lh, 0);
bp = m_prepend(bp, lhp, sizeof *lhp, 2);
m->m_next = m_prepend(NULL, v, sz, 0);
bp = m_prepend(NULL, v, sz, 0);
extern struct mbuf *m_prepend(struct mbuf *, const void *, size_t, u_short);
m = m_prepend(m, prepend, 2, 0);
m = m_prepend(m, prepend, 4, 0);
bp = m_prepend(bp, cp + 1, 1, extra);
bp = m_prepend(bp, cp, 2, extra);
bp = m_prepend(bp, bufp, len, 0);