Function uipc_send

freebsd/kern/uipc_usrreq.c:997–1183

}

static int
uipc_send(struct socket *so, int flags, struct mbuf *m, struct sockaddr *nam,
    struct mbuf *control, struct thread *td)
{
	struct unpcb *unp, *unp2;
	struct socket *so2;
	u_int mbcnt, sbcc;
	int freed, error;

	unp = sotounpcb(so);
	KASSERT(unp != NULL, ("%s: unp == NULL", __func__));
	KASSERT(so->so_type == SOCK_STREAM || so->so_type == SOCK_DGRAM ||
	    so->so_type == SOCK_SEQPACKET,
	    ("%s: socktype %d", __func__, so->so_type));

	freed = error = 0;
	if (flags & PRUS_OOB) {
		error = EOPNOTSUPP;
		goto release;
	}
	if (control != NULL && (error = unp_internalize(&control, td)))
		goto release;

	unp2 = NULL;
	switch (so->so_type) {
	case SOCK_DGRAM:
	{
		const struct sockaddr *from;

		if (nam != NULL) {
			error = unp_connect(so, nam, td);
			if (error != 0)
				break;
		}
		UNP_PCB_LOCK(unp);

		/*
		 * Because connect() and send() are non-atomic in a sendto()
		 * with a target address, it's possible that the socket will
		 * have disconnected before the send() can run.  In that case
		 * return the slightly counter-intuitive but otherwise
		 * correct error that the socket is not connected.
		 */
		unp2 = unp_pcb_lock_peer(unp);
		if (unp2 == NULL) {
			UNP_PCB_UNLOCK(unp);
			error = ENOTCONN;
			break;
		}

		if (unp2->unp_flags & UNP_WANTCRED_MASK)
			control = unp_addsockcred(td, control,
			    unp2->unp_flags);
		if (unp->unp_addr != NULL)
			from = (struct sockaddr *)unp->unp_addr;
		else
			from = &sun_noname;
		so2 = unp2->unp_socket;