m_xhalf
uint32_t m_xhalf(const struct mbuf *, uint32_t, int *);
#define xhalf(p, k, err) m_xhalf((const struct mbuf *)(p), (k), (err))
uint32_t m_xhalf(const struct mbuf *, uint32_t, int *);
ret0, ret0_size, ret0_maxsize, &m_xhalf);