ipv4: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Notice that in some cases I placed the "fall through" comment
on its own line, which is what GCC is expecting to find.

Addresses-Coverity-ID: 115108
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/af_inet.c

@@ -827,6 +827,7 @@ int inet_shutdown(struct socket *sock, int how)
 		err = -ENOTCONN;
 		/* Hack to wake up other listeners, who can poll for
 		   POLLHUP, even on eg. unconnected UDP sockets -- RR */
+		/* fall through */
 	default:
 		sk->sk_shutdown |= how;
 		if (sk->sk_prot->shutdown)
@@ -840,7 +841,7 @@ int inet_shutdown(struct socket *sock, int how)
 	case TCP_LISTEN:
 		if (!(how & RCV_SHUTDOWN))
 			break;
-		/* Fall through */
+		/* fall through */
 	case TCP_SYN_SENT:
 		err = sk->sk_prot->disconnect(sk, O_NONBLOCK);
 		sock->state = err ? SS_DISCONNECTING : SS_UNCONNECTED;

net/ipv4/arp.c

@@ -1180,6 +1180,7 @@ int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
 	case SIOCSARP:
 		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
 			return -EPERM;
+		/* fall through */
 	case SIOCGARP:
 		err = copy_from_user(&r, arg, sizeof(struct arpreq));
 		if (err)

net/ipv4/devinet.c

@@ -1522,6 +1522,7 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
 		if (inetdev_valid_mtu(dev->mtu))
 			break;
 		/* disable IP when MTU is not enough */
+		/* fall through */
 	case NETDEV_UNREGISTER:
 		inetdev_destroy(in_dev);
 		break;

net/ipv4/ipmr.c

@@ -1528,6 +1528,7 @@ int ip_mroute_setsockopt(struct sock *sk, int optname, char __user *optval,
 	case MRT_ADD_MFC:
 	case MRT_DEL_MFC:
 		parent = -1;
+		/* fall through */
 	case MRT_ADD_MFC_PROXY:
 	case MRT_DEL_MFC_PROXY:
 		if (optlen != sizeof(mfc)) {

net/ipv4/netfilter/nf_nat_l3proto_ipv4.c

@@ -276,7 +276,8 @@ nf_nat_ipv4_fn(void *priv, struct sk_buff *skb,
 			else
 				return NF_ACCEPT;
 		}
-		/* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
+		/* Only ICMPs can be IP_CT_IS_REPLY: */
+		/* fall through */
 	case IP_CT_NEW:
 		/* Seen it before?  This can happen for loopback, retrans,
 		 * or local packets.

net/ipv4/tcp_input.c

@@ -2885,6 +2885,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 		      (*ack_flag & FLAG_LOST_RETRANS)))
 			return;
 		/* Change state if cwnd is undone or retransmits are lost */
+		/* fall through */
 	default:
 		if (tcp_is_reno(tp)) {
 			if (flag & FLAG_SND_UNA_ADVANCED)
@@ -6044,6 +6045,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 	case TCP_LAST_ACK:
 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
 			break;
+		/* fall through */
 	case TCP_FIN_WAIT1:
 	case TCP_FIN_WAIT2:
 		/* RFC 793 says to queue data in these states,

net/ipv4/tcp_ipv4.c

@@ -1779,8 +1779,9 @@ int tcp_v4_rcv(struct sk_buff *skb)
 			refcounted = false;
 			goto process;
 		}
-		/* Fall through to ACK */
 	}
+		/* to ACK */
+		/* fall through */
 	case TCP_TW_ACK:
 		tcp_v4_timewait_ack(sk, skb);
 		break;