[TCP/DCCP]: Introduce net_xmit_eval

Throughout the TCP/DCCP (and tunnelling) code, it often happens that the
return code of a transmit function needs to be tested against NET_XMIT_CN
which is a value that does not indicate a strict error condition.

This patch uses a macro for these recurring situations which is consistent
with the already existing macro net_xmit_errno, saving on duplicated code.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

include/linux/netdevice.h

@@ -66,6 +66,10 @@ struct netpoll_info;
 #define NET_RX_CN_HIGH		4   /* The storm is here */
 #define NET_RX_BAD		5  /* packet dropped due to kernel error */
 
+/* NET_XMIT_CN is special. It does not guarantee that this packet is lost. It
+ * indicates that the device will soon be dropping packets, or already drops
+ * some packets of the same priority; prompting us to send less aggressively. */
+#define net_xmit_eval(e)	((e) == NET_XMIT_CN? 0 : (e))
 #define net_xmit_errno(e)	((e) != NET_XMIT_CN ? -ENOBUFS : 0)
 
 #endif

include/net/ipip.h

@@ -35,7 +35,7 @@ struct ip_tunnel
 	ip_send_check(iph);						\
 									\
 	err = NF_HOOK(PF_INET, NF_IP_LOCAL_OUT, skb, NULL, rt->u.dst.dev, dst_output);\
-	if (err == NET_XMIT_SUCCESS || err == NET_XMIT_CN) {		\
+	if (net_xmit_eval(err) == 0) {					\
 		stats->tx_bytes += pkt_len;				\
 		stats->tx_packets++;					\
 	} else {							\

net/dccp/ipv4.c

@@ -501,8 +501,7 @@ static int dccp_v4_send_response(struct sock *sk, struct request_sock *req,
 		err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
 					    ireq->rmt_addr,
 					    ireq->opt);
-		if (err == NET_XMIT_CN)
-			err = 0;
+		err = net_xmit_eval(err);
 	}
 
 out:
@@ -571,7 +570,7 @@ static void dccp_v4_ctl_send_reset(struct sk_buff *rxskb)
 				    rxskb->nh.iph->saddr, NULL);
 	bh_unlock_sock(dccp_v4_ctl_socket->sk);
 
-	if (err == NET_XMIT_CN || err == 0) {
+	if (net_xmit_eval(err) == 0) {
 		DCCP_INC_STATS_BH(DCCP_MIB_OUTSEGS);
 		DCCP_INC_STATS_BH(DCCP_MIB_OUTRSTS);
 	}

net/dccp/ipv6.c

@@ -294,8 +294,7 @@ static int dccp_v6_send_response(struct sock *sk, struct request_sock *req,
 							 &ireq6->rmt_addr);
 		ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
 		err = ip6_xmit(sk, skb, &fl, opt, 0);
-		if (err == NET_XMIT_CN)
-			err = 0;
+		err = net_xmit_eval(err);
 	}
 
 done:

net/dccp/output.c

@@ -125,16 +125,7 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
 
 		memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 		err = icsk->icsk_af_ops->queue_xmit(skb, sk, 0);
-		if (err <= 0)
-			return err;
-
-		/* NET_XMIT_CN is special. It does not guarantee,
-		 * that this packet is lost. It tells that device
-		 * is about to start to drop packets or already
-		 * drops some packets of the same priority and
-		 * invokes us to send less aggressively.
-		 */
-		return err == NET_XMIT_CN ? 0 : err;
+		return net_xmit_eval(err);
 	}
 	return -ENOBUFS;
 }
@@ -426,8 +417,7 @@ int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
 		if (skb != NULL) {
 			memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 			err = inet_csk(sk)->icsk_af_ops->queue_xmit(skb, sk, 0);
-			if (err == NET_XMIT_CN)
-				err = 0;
+			return net_xmit_eval(err);
 		}
 	}
 

net/ipv4/tcp_ipv4.c

@@ -662,8 +662,7 @@ static int tcp_v4_send_synack(struct sock *sk, struct request_sock *req,
 		err = ip_build_and_send_pkt(skb, sk, ireq->loc_addr,
 					    ireq->rmt_addr,
 					    ireq->opt);
-		if (err == NET_XMIT_CN)
-			err = 0;
+		err = net_xmit_eval(err);
 	}
 
 out:

net/ipv4/tcp_output.c

@@ -484,13 +484,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 
 	tcp_enter_cwr(sk);
 
-	/* NET_XMIT_CN is special. It does not guarantee,
-	 * that this packet is lost. It tells that device
-	 * is about to start to drop packets or already
-	 * drops some packets of the same priority and
-	 * invokes us to send less aggressively.
-	 */
-	return err == NET_XMIT_CN ? 0 : err;
+	return net_xmit_eval(err);
 
 #undef SYSCTL_FLAG_TSTAMPS
 #undef SYSCTL_FLAG_WSCALE

net/ipv6/ip6_tunnel.c

@@ -748,7 +748,7 @@ ip6ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 	err = NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, skb, NULL, 
 		      skb->dst->dev, dst_output);
 
-	if (err == NET_XMIT_SUCCESS || err == NET_XMIT_CN) {
+	if (net_xmit_eval(err) == 0) {
 		stats->tx_bytes += pkt_len;
 		stats->tx_packets++;
 	} else {

net/ipv6/tcp_ipv6.c

@@ -502,8 +502,7 @@ static int tcp_v6_send_synack(struct sock *sk, struct request_sock *req,
 
 		ipv6_addr_copy(&fl.fl6_dst, &treq->rmt_addr);
 		err = ip6_xmit(sk, skb, &fl, opt, 0);
-		if (err == NET_XMIT_CN)
-			err = 0;
+		err = net_xmit_eval(err);
 	}
 
 done: