// SPDX-License-Identifier: GPL-2.0-or-later

  /* RxRPC packet transmission
   *
   * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/net.h>

  #include <linux/gfp.h>

  #include <linux/skbuff.h>

  #include <linux/export.h>

  #include <net/sock.h>
  #include <net/af_rxrpc.h>
  #include "ar-internal.h"

  struct rxrpc_ack_buffer {

  	struct rxrpc_wire_header whdr;

  	struct rxrpc_ackpacket ack;
  	u8 acks[255];
  	u8 pad[3];

  	struct rxrpc_ackinfo ackinfo;
  };

  struct rxrpc_abort_buffer {
  	struct rxrpc_wire_header whdr;
  	__be32 abort_code;
  };

  static const char rxrpc_keepalive_string[] = "";

  /*

   * Increase Tx backoff on transmission failure and clear it on success.
   */
  static void rxrpc_tx_backoff(struct rxrpc_call *call, int ret)
  {
  	if (ret < 0) {
  		u16 tx_backoff = READ_ONCE(call->tx_backoff);
  
  		if (tx_backoff < HZ)
  			WRITE_ONCE(call->tx_backoff, tx_backoff + 1);
  	} else {
  		WRITE_ONCE(call->tx_backoff, 0);
  	}
  }
  
  /*

   * Arrange for a keepalive ping a certain time after we last transmitted.  This
   * lets the far side know we're still interested in this call and helps keep
   * the route through any intervening firewall open.
   *
   * Receiving a response to the ping will prevent the ->expect_rx_by timer from
   * expiring.
   */
  static void rxrpc_set_keepalive(struct rxrpc_call *call)
  {
  	unsigned long now = jiffies, keepalive_at = call->next_rx_timo / 6;
  
  	keepalive_at += now;
  	WRITE_ONCE(call->keepalive_at, keepalive_at);
  	rxrpc_reduce_call_timer(call, keepalive_at, now,
  				rxrpc_timer_set_for_keepalive);
  }
  
  /*

   * Fill out an ACK packet.
   */

  static size_t rxrpc_fill_out_ack(struct rxrpc_connection *conn,
  				 struct rxrpc_call *call,

  				 struct rxrpc_ack_buffer *pkt,

  				 rxrpc_seq_t *_hard_ack,

  				 rxrpc_seq_t *_top,
  				 u8 reason)

  {

  	rxrpc_serial_t serial;

  	rxrpc_seq_t hard_ack, top, seq;
  	int ix;

  	u32 mtu, jmax;
  	u8 *ackp = pkt->acks;

  	/* Barrier against rxrpc_input_data(). */

  	serial = call->ackr_serial;

  	hard_ack = READ_ONCE(call->rx_hard_ack);
  	top = smp_load_acquire(&call->rx_top);

  	*_hard_ack = hard_ack;
  	*_top = top;

  	pkt->ack.bufferSpace	= htons(8);

  	pkt->ack.maxSkew	= htons(0);

  	pkt->ack.firstPacket	= htonl(hard_ack + 1);

  	pkt->ack.previousPacket	= htonl(call->ackr_prev_seq);

  	pkt->ack.serial		= htonl(serial);

  	pkt->ack.reason		= reason;

  	pkt->ack.nAcks		= top - hard_ack;

  	if (reason == RXRPC_ACK_PING)

  		pkt->whdr.flags |= RXRPC_REQUEST_ACK;

  	if (after(top, hard_ack)) {
  		seq = hard_ack + 1;
  		do {
  			ix = seq & RXRPC_RXTX_BUFF_MASK;
  			if (call->rxtx_buffer[ix])
  				*ackp++ = RXRPC_ACK_TYPE_ACK;
  			else
  				*ackp++ = RXRPC_ACK_TYPE_NACK;
  			seq++;
  		} while (before_eq(seq, top));
  	}

  	mtu = conn->params.peer->if_mtu;
  	mtu -= conn->params.peer->hdrsize;

  	jmax = (call->nr_jumbo_bad > 3) ? 1 : rxrpc_rx_jumbo_max;

  	pkt->ackinfo.rxMTU	= htonl(rxrpc_rx_mtu);
  	pkt->ackinfo.maxMTU	= htonl(mtu);

  	pkt->ackinfo.rwind	= htonl(call->rx_winsize);

  	pkt->ackinfo.jumbo_max	= htonl(jmax);
  
  	*ackp++ = 0;
  	*ackp++ = 0;
  	*ackp++ = 0;

  	return top - hard_ack + 3;

  }
  
  /*

   * Record the beginning of an RTT probe.
   */
  static int rxrpc_begin_rtt_probe(struct rxrpc_call *call, rxrpc_serial_t serial,
  				 enum rxrpc_rtt_tx_trace why)
  {
  	unsigned long avail = call->rtt_avail;
  	int rtt_slot = 9;
  
  	if (!(avail & RXRPC_CALL_RTT_AVAIL_MASK))
  		goto no_slot;
  
  	rtt_slot = __ffs(avail & RXRPC_CALL_RTT_AVAIL_MASK);
  	if (!test_and_clear_bit(rtt_slot, &call->rtt_avail))
  		goto no_slot;
  
  	call->rtt_serial[rtt_slot] = serial;
  	call->rtt_sent_at[rtt_slot] = ktime_get_real();
  	smp_wmb(); /* Write data before avail bit */
  	set_bit(rtt_slot + RXRPC_CALL_RTT_PEND_SHIFT, &call->rtt_avail);
  
  	trace_rxrpc_rtt_tx(call, why, rtt_slot, serial);
  	return rtt_slot;
  
  no_slot:
  	trace_rxrpc_rtt_tx(call, rxrpc_rtt_tx_no_slot, rtt_slot, serial);
  	return -1;
  }
  
  /*
   * Cancel an RTT probe.
   */
  static void rxrpc_cancel_rtt_probe(struct rxrpc_call *call,
  				   rxrpc_serial_t serial, int rtt_slot)
  {
  	if (rtt_slot != -1) {
  		clear_bit(rtt_slot + RXRPC_CALL_RTT_PEND_SHIFT, &call->rtt_avail);
  		smp_wmb(); /* Clear pending bit before setting slot */
  		set_bit(rtt_slot, &call->rtt_avail);
  		trace_rxrpc_rtt_tx(call, rxrpc_rtt_tx_cancel, rtt_slot, serial);
  	}
  }
  
  /*

   * Send an ACK call packet.

   */

  int rxrpc_send_ack_packet(struct rxrpc_call *call, bool ping,
  			  rxrpc_serial_t *_serial)

  {

  	struct rxrpc_connection *conn;

  	struct rxrpc_ack_buffer *pkt;

  	struct msghdr msg;
  	struct kvec iov[2];
  	rxrpc_serial_t serial;

  	rxrpc_seq_t hard_ack, top;

  	size_t len, n;

  	int ret, rtt_slot = -1;

  	u8 reason;

  	if (test_bit(RXRPC_CALL_DISCONNECTED, &call->flags))

  		return -ECONNRESET;
  
  	pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);

  	if (!pkt)

  		return -ENOMEM;

  
  	conn = call->conn;

  	msg.msg_name	= &call->peer->srx.transport;
  	msg.msg_namelen	= call->peer->srx.transport_len;
  	msg.msg_control	= NULL;
  	msg.msg_controllen = 0;
  	msg.msg_flags	= 0;
  
  	pkt->whdr.epoch		= htonl(conn->proto.epoch);
  	pkt->whdr.cid		= htonl(call->cid);
  	pkt->whdr.callNumber	= htonl(call->call_id);
  	pkt->whdr.seq		= 0;

  	pkt->whdr.type		= RXRPC_PACKET_TYPE_ACK;
  	pkt->whdr.flags		= RXRPC_SLOW_START_OK | conn->out_clientflag;

  	pkt->whdr.userStatus	= 0;
  	pkt->whdr.securityIndex	= call->security_ix;
  	pkt->whdr._rsvd		= 0;
  	pkt->whdr.serviceId	= htons(call->service_id);

  	spin_lock_bh(&call->lock);

  	if (ping) {
  		reason = RXRPC_ACK_PING;
  	} else {
  		reason = call->ackr_reason;
  		if (!call->ackr_reason) {
  			spin_unlock_bh(&call->lock);
  			ret = 0;
  			goto out;
  		}
  		call->ackr_reason = 0;

  	}

  	n = rxrpc_fill_out_ack(conn, call, pkt, &hard_ack, &top, reason);

  
  	spin_unlock_bh(&call->lock);
  
  	iov[0].iov_base	= pkt;
  	iov[0].iov_len	= sizeof(pkt->whdr) + sizeof(pkt->ack) + n;
  	iov[1].iov_base = &pkt->ackinfo;
  	iov[1].iov_len	= sizeof(pkt->ackinfo);
  	len = iov[0].iov_len + iov[1].iov_len;

  	serial = atomic_inc_return(&conn->serial);
  	pkt->whdr.serial = htonl(serial);

  	trace_rxrpc_tx_ack(call->debug_id, serial,

  			   ntohl(pkt->ack.firstPacket),
  			   ntohl(pkt->ack.serial),
  			   pkt->ack.reason, pkt->ack.nAcks);

  	if (_serial)
  		*_serial = serial;

  	if (ping)
  		rtt_slot = rxrpc_begin_rtt_probe(call, serial, rxrpc_rtt_tx_ping);

  
  	ret = kernel_sendmsg(conn->params.local->socket, &msg, iov, 2, len);

  	conn->params.peer->last_tx_at = ktime_get_seconds();

  	if (ret < 0)
  		trace_rxrpc_tx_fail(call->debug_id, serial, ret,

  				    rxrpc_tx_point_call_ack);
  	else
  		trace_rxrpc_tx_packet(call->debug_id, &pkt->whdr,
  				      rxrpc_tx_point_call_ack);

  	rxrpc_tx_backoff(call, ret);

  	if (call->state < RXRPC_CALL_COMPLETE) {

  		if (ret < 0) {

  			rxrpc_cancel_rtt_probe(call, serial, rtt_slot);

  			rxrpc_propose_ACK(call, pkt->ack.reason,

  					  ntohl(pkt->ack.serial),

  					  false, true,

  					  rxrpc_propose_ack_retry_tx);

  		} else {
  			spin_lock_bh(&call->lock);
  			if (after(hard_ack, call->ackr_consumed))
  				call->ackr_consumed = hard_ack;
  			if (after(top, call->ackr_seen))
  				call->ackr_seen = top;
  			spin_unlock_bh(&call->lock);

  		}

  
  		rxrpc_set_keepalive(call);

  	}

  out:

  	kfree(pkt);
  	return ret;
  }

  /*

   * Send an ABORT call packet.
   */
  int rxrpc_send_abort_packet(struct rxrpc_call *call)
  {

  	struct rxrpc_connection *conn;

  	struct rxrpc_abort_buffer pkt;
  	struct msghdr msg;
  	struct kvec iov[1];
  	rxrpc_serial_t serial;
  	int ret;

  	/* Don't bother sending aborts for a client call once the server has
  	 * hard-ACK'd all of its request data.  After that point, we're not
  	 * going to stop the operation proceeding, and whilst we might limit
  	 * the reply, it's not worth it if we can send a new call on the same
  	 * channel instead, thereby closing off this call.
  	 */
  	if (rxrpc_is_client_call(call) &&
  	    test_bit(RXRPC_CALL_TX_LAST, &call->flags))
  		return 0;

  	if (test_bit(RXRPC_CALL_DISCONNECTED, &call->flags))

  		return -ECONNRESET;

  	conn = call->conn;

  	msg.msg_name	= &call->peer->srx.transport;
  	msg.msg_namelen	= call->peer->srx.transport_len;
  	msg.msg_control	= NULL;
  	msg.msg_controllen = 0;
  	msg.msg_flags	= 0;
  
  	pkt.whdr.epoch		= htonl(conn->proto.epoch);
  	pkt.whdr.cid		= htonl(call->cid);
  	pkt.whdr.callNumber	= htonl(call->call_id);
  	pkt.whdr.seq		= 0;
  	pkt.whdr.type		= RXRPC_PACKET_TYPE_ABORT;
  	pkt.whdr.flags		= conn->out_clientflag;
  	pkt.whdr.userStatus	= 0;
  	pkt.whdr.securityIndex	= call->security_ix;
  	pkt.whdr._rsvd		= 0;
  	pkt.whdr.serviceId	= htons(call->service_id);
  	pkt.abort_code		= htonl(call->abort_code);
  
  	iov[0].iov_base	= &pkt;
  	iov[0].iov_len	= sizeof(pkt);
  
  	serial = atomic_inc_return(&conn->serial);
  	pkt.whdr.serial = htonl(serial);
  
  	ret = kernel_sendmsg(conn->params.local->socket,
  			     &msg, iov, 1, sizeof(pkt));

  	conn->params.peer->last_tx_at = ktime_get_seconds();

  	if (ret < 0)
  		trace_rxrpc_tx_fail(call->debug_id, serial, ret,

  				    rxrpc_tx_point_call_abort);
  	else
  		trace_rxrpc_tx_packet(call->debug_id, &pkt.whdr,
  				      rxrpc_tx_point_call_abort);

  	rxrpc_tx_backoff(call, ret);

  	return ret;
  }
  
  /*

   * send a packet through the transport endpoint
   */

  int rxrpc_send_data_packet(struct rxrpc_call *call, struct sk_buff *skb,
  			   bool retrans)

  {

  	struct rxrpc_connection *conn = call->conn;
  	struct rxrpc_wire_header whdr;
  	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);

  	struct msghdr msg;

  	struct kvec iov[2];
  	rxrpc_serial_t serial;
  	size_t len;

  	int ret, rtt_slot = -1;

  
  	_enter(",{%d}", skb->len);

  	if (hlist_unhashed(&call->error_link)) {
  		spin_lock_bh(&call->peer->lock);
  		hlist_add_head_rcu(&call->error_link, &call->peer->error_targets);
  		spin_unlock_bh(&call->peer->lock);
  	}

  	/* Each transmission of a Tx packet needs a new serial number */
  	serial = atomic_inc_return(&conn->serial);

  	whdr.epoch	= htonl(conn->proto.epoch);
  	whdr.cid	= htonl(call->cid);
  	whdr.callNumber	= htonl(call->call_id);
  	whdr.seq	= htonl(sp->hdr.seq);
  	whdr.serial	= htonl(serial);
  	whdr.type	= RXRPC_PACKET_TYPE_DATA;
  	whdr.flags	= sp->hdr.flags;
  	whdr.userStatus	= 0;
  	whdr.securityIndex = call->security_ix;
  	whdr._rsvd	= htons(sp->hdr._rsvd);
  	whdr.serviceId	= htons(call->service_id);

  	if (test_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags) &&
  	    sp->hdr.seq == 1)
  		whdr.userStatus	= RXRPC_USERSTATUS_SERVICE_UPGRADE;

  	iov[0].iov_base = &whdr;
  	iov[0].iov_len = sizeof(whdr);
  	iov[1].iov_base = skb->head;
  	iov[1].iov_len = skb->len;
  	len = iov[0].iov_len + iov[1].iov_len;
  
  	msg.msg_name = &call->peer->srx.transport;
  	msg.msg_namelen = call->peer->srx.transport_len;

  	msg.msg_control = NULL;
  	msg.msg_controllen = 0;
  	msg.msg_flags = 0;

  	/* If our RTT cache needs working on, request an ACK.  Also request
  	 * ACKs if a DATA packet appears to have been lost.

  	 *
  	 * However, we mustn't request an ACK on the last reply packet of a
  	 * service call, lest OpenAFS incorrectly send us an ACK with some
  	 * soft-ACKs in it and then never follow up with a proper hard ACK.

  	 */

  	if ((!(sp->hdr.flags & RXRPC_LAST_PACKET) ||
  	     rxrpc_to_server(sp)
  	     ) &&

  	    (test_and_clear_bit(RXRPC_CALL_EV_ACK_LOST, &call->events) ||
  	     retrans ||

  	     call->cong_mode == RXRPC_CALL_SLOW_START ||

  	     (call->peer->rtt_count < 3 && sp->hdr.seq & 1) ||

  	     ktime_before(ktime_add_ms(call->peer->rtt_last_req, 1000),
  			  ktime_get_real())))

  		whdr.flags |= RXRPC_REQUEST_ACK;

  	if (IS_ENABLED(CONFIG_AF_RXRPC_INJECT_LOSS)) {
  		static int lose;
  		if ((lose++ & 7) == 7) {

  			ret = 0;

  			trace_rxrpc_tx_data(call, sp->hdr.seq, serial,
  					    whdr.flags, retrans, true);
  			goto done;

  		}
  	}

  	trace_rxrpc_tx_data(call, sp->hdr.seq, serial, whdr.flags, retrans,
  			    false);

  	/* send the packet with the don't fragment bit set if we currently
  	 * think it's small enough */

  	if (iov[1].iov_len >= call->peer->maxdata)
  		goto send_fragmentable;
  
  	down_read(&conn->params.local->defrag_sem);

  
  	sp->hdr.serial = serial;
  	smp_wmb(); /* Set serial before timestamp */
  	skb->tstamp = ktime_get_real();

  	if (whdr.flags & RXRPC_REQUEST_ACK)
  		rtt_slot = rxrpc_begin_rtt_probe(call, serial, rxrpc_rtt_tx_data);

  	/* send the packet by UDP
  	 * - returns -EMSGSIZE if UDP would have to fragment the packet
  	 *   to go out of the interface
  	 *   - in which case, we'll have processed the ICMP error
  	 *     message and update the peer record
  	 */
  	ret = kernel_sendmsg(conn->params.local->socket, &msg, iov, 2, len);

  	conn->params.peer->last_tx_at = ktime_get_seconds();

  
  	up_read(&conn->params.local->defrag_sem);

  	if (ret < 0) {
  		rxrpc_cancel_rtt_probe(call, serial, rtt_slot);

  		trace_rxrpc_tx_fail(call->debug_id, serial, ret,

  				    rxrpc_tx_point_call_data_nofrag);

  	} else {

  		trace_rxrpc_tx_packet(call->debug_id, &whdr,
  				      rxrpc_tx_point_call_data_nofrag);

  	}

  	rxrpc_tx_backoff(call, ret);

  	if (ret == -EMSGSIZE)
  		goto send_fragmentable;
  
  done:

  	if (ret >= 0) {

  		if (whdr.flags & RXRPC_REQUEST_ACK) {

  			call->peer->rtt_last_req = skb->tstamp;

  			if (call->peer->rtt_count > 1) {

  				unsigned long nowj = jiffies, ack_lost_at;

  				ack_lost_at = rxrpc_get_rto_backoff(call->peer, retrans);

  				ack_lost_at += nowj;
  				WRITE_ONCE(call->ack_lost_at, ack_lost_at);
  				rxrpc_reduce_call_timer(call, ack_lost_at, nowj,
  							rxrpc_timer_set_for_lost_ack);
  			}

  		}

  
  		if (sp->hdr.seq == 1 &&
  		    !test_and_set_bit(RXRPC_CALL_BEGAN_RX_TIMER,
  				      &call->flags)) {
  			unsigned long nowj = jiffies, expect_rx_by;
  
  			expect_rx_by = nowj + call->next_rx_timo;
  			WRITE_ONCE(call->expect_rx_by, expect_rx_by);
  			rxrpc_reduce_call_timer(call, expect_rx_by, nowj,
  						rxrpc_timer_set_for_normal);
  		}

  		rxrpc_set_keepalive(call);
  	} else {
  		/* Cancel the call if the initial transmission fails,
  		 * particularly if that's due to network routing issues that
  		 * aren't going away anytime soon.  The layer above can arrange
  		 * the retransmission.
  		 */
  		if (!test_and_set_bit(RXRPC_CALL_BEGAN_RX_TIMER, &call->flags))
  			rxrpc_set_call_completion(call, RXRPC_CALL_LOCAL_ERROR,
  						  RX_USER_ABORT, ret);
  	}

  	_leave(" = %d [%u]", ret, call->peer->maxdata);
  	return ret;

  
  send_fragmentable:
  	/* attempt to send this message with fragmentation enabled */
  	_debug("send fragment");

  	down_write(&conn->params.local->defrag_sem);

  	sp->hdr.serial = serial;
  	smp_wmb(); /* Set serial before timestamp */
  	skb->tstamp = ktime_get_real();

  	if (whdr.flags & RXRPC_REQUEST_ACK)
  		rtt_slot = rxrpc_begin_rtt_probe(call, serial, rxrpc_rtt_tx_data);

  	switch (conn->params.local->srx.transport.family) {

  	case AF_INET6:

  	case AF_INET:

  		ip_sock_set_mtu_discover(conn->params.local->socket->sk,
  				IP_PMTUDISC_DONT);

  		ret = kernel_sendmsg(conn->params.local->socket, &msg,
  				     iov, 2, len);
  		conn->params.peer->last_tx_at = ktime_get_seconds();

  		ip_sock_set_mtu_discover(conn->params.local->socket->sk,
  				IP_PMTUDISC_DO);

  		break;

  
  	default:
  		BUG();

  	}

  	if (ret < 0) {
  		rxrpc_cancel_rtt_probe(call, serial, rtt_slot);

  		trace_rxrpc_tx_fail(call->debug_id, serial, ret,

  				    rxrpc_tx_point_call_data_frag);

  	} else {

  		trace_rxrpc_tx_packet(call->debug_id, &whdr,
  				      rxrpc_tx_point_call_data_frag);

  	}

  	rxrpc_tx_backoff(call, ret);

  	up_write(&conn->params.local->defrag_sem);

  	goto done;

  }

  
  /*
   * reject packets through the local endpoint
   */
  void rxrpc_reject_packets(struct rxrpc_local *local)
  {

  	struct sockaddr_rxrpc srx;

  	struct rxrpc_skb_priv *sp;
  	struct rxrpc_wire_header whdr;
  	struct sk_buff *skb;
  	struct msghdr msg;
  	struct kvec iov[2];
  	size_t size;
  	__be32 code;

  	int ret, ioc;

  
  	_enter("%d", local->debug_id);
  
  	iov[0].iov_base = &whdr;
  	iov[0].iov_len = sizeof(whdr);
  	iov[1].iov_base = &code;
  	iov[1].iov_len = sizeof(code);

  	msg.msg_name = &srx.transport;

  	msg.msg_control = NULL;
  	msg.msg_controllen = 0;
  	msg.msg_flags = 0;

  	memset(&whdr, 0, sizeof(whdr));

  
  	while ((skb = skb_dequeue(&local->reject_queue))) {

  		rxrpc_see_skb(skb, rxrpc_skb_seen);

  		sp = rxrpc_skb(skb);

  		switch (skb->mark) {
  		case RXRPC_SKB_MARK_REJECT_BUSY:
  			whdr.type = RXRPC_PACKET_TYPE_BUSY;
  			size = sizeof(whdr);
  			ioc = 1;
  			break;
  		case RXRPC_SKB_MARK_REJECT_ABORT:
  			whdr.type = RXRPC_PACKET_TYPE_ABORT;
  			code = htonl(skb->priority);
  			size = sizeof(whdr) + sizeof(code);
  			ioc = 2;
  			break;
  		default:

  			rxrpc_free_skb(skb, rxrpc_skb_freed);

  			continue;
  		}

  		if (rxrpc_extract_addr_from_skb(&srx, skb) == 0) {

  			msg.msg_namelen = srx.transport_len;

  			whdr.epoch	= htonl(sp->hdr.epoch);
  			whdr.cid	= htonl(sp->hdr.cid);
  			whdr.callNumber	= htonl(sp->hdr.callNumber);
  			whdr.serviceId	= htons(sp->hdr.serviceId);
  			whdr.flags	= sp->hdr.flags;
  			whdr.flags	^= RXRPC_CLIENT_INITIATED;
  			whdr.flags	&= RXRPC_CLIENT_INITIATED;

  			ret = kernel_sendmsg(local->socket, &msg,
  					     iov, ioc, size);

  			if (ret < 0)
  				trace_rxrpc_tx_fail(local->debug_id, 0, ret,

  						    rxrpc_tx_point_reject);
  			else
  				trace_rxrpc_tx_packet(local->debug_id, &whdr,
  						      rxrpc_tx_point_reject);

  		}

  		rxrpc_free_skb(skb, rxrpc_skb_freed);

  	}
  
  	_leave("");
  }

  
  /*
   * Send a VERSION reply to a peer as a keepalive.
   */
  void rxrpc_send_keepalive(struct rxrpc_peer *peer)
  {
  	struct rxrpc_wire_header whdr;
  	struct msghdr msg;
  	struct kvec iov[2];
  	size_t len;
  	int ret;
  
  	_enter("");
  
  	msg.msg_name	= &peer->srx.transport;
  	msg.msg_namelen	= peer->srx.transport_len;
  	msg.msg_control	= NULL;
  	msg.msg_controllen = 0;
  	msg.msg_flags	= 0;
  
  	whdr.epoch	= htonl(peer->local->rxnet->epoch);
  	whdr.cid	= 0;
  	whdr.callNumber	= 0;
  	whdr.seq	= 0;
  	whdr.serial	= 0;
  	whdr.type	= RXRPC_PACKET_TYPE_VERSION; /* Not client-initiated */
  	whdr.flags	= RXRPC_LAST_PACKET;
  	whdr.userStatus	= 0;
  	whdr.securityIndex = 0;
  	whdr._rsvd	= 0;
  	whdr.serviceId	= 0;
  
  	iov[0].iov_base	= &whdr;
  	iov[0].iov_len	= sizeof(whdr);
  	iov[1].iov_base	= (char *)rxrpc_keepalive_string;
  	iov[1].iov_len	= sizeof(rxrpc_keepalive_string);
  
  	len = iov[0].iov_len + iov[1].iov_len;
  
  	_proto("Tx VERSION (keepalive)");
  
  	ret = kernel_sendmsg(peer->local->socket, &msg, iov, 2, len);
  	if (ret < 0)

  		trace_rxrpc_tx_fail(peer->debug_id, 0, ret,

  				    rxrpc_tx_point_version_keepalive);
  	else
  		trace_rxrpc_tx_packet(peer->debug_id, &whdr,
  				      rxrpc_tx_point_version_keepalive);

  	peer->last_tx_at = ktime_get_seconds();

  	_leave("");
  }