c_caddr_t
int m_append(struct mbuf*, int, c_caddr_t);
void m_copyback(struct mbuf *m0, int off, int len, c_caddr_t cp);
m_copyback(struct mbuf *m0, int off, int len, c_caddr_t cp)
m_append(struct mbuf *m0, int len, c_caddr_t cp)