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