ipv6: Introduce ip6_flow_hdr() to fill version, tclass and flowlabel.

This is not only for readability but also for optimization.
What we do here is to build the 32bit word at the beginning of the ipv6
header (the "ip6_flow" virtual member of struct ip6_hdr in RFC3542) and
we do not need to read the tclass portion of the target buffer.
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ipv6.h

@@ -546,6 +546,15 @@ static inline int ipv6_addr_diff(const struct in6_addr *a1, const struct in6_add
 
 extern void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt);
 
+/*
+ *	Header manipulation
+ */
+static inline void ip6_flow_hdr(struct ipv6hdr *hdr, unsigned int tclass,
+				__be32 flowlabel)
+{
+	*(__be32 *)hdr = ntohl(0x60000000 | (tclass << 20)) | flowlabel;
+}
+
 /*
  *	Prototypes exported by ipv6
  */

net/ipv6/ip6_gre.c

@@ -772,9 +772,7 @@ static netdev_tx_t ip6gre_xmit2(struct sk_buff *skb,
 	 *	Push down and install the IP header.
 	 */
 	ipv6h = ipv6_hdr(skb);
-	*(__be32 *)ipv6h = fl6->flowlabel | htonl(0x60000000);
-	dsfield = INET_ECN_encapsulate(0, dsfield);
-	ipv6_change_dsfield(ipv6h, ~INET_ECN_MASK, dsfield);
+	ip6_flow_hdr(ipv6h, INET_ECN_encapsulate(0, dsfield), fl6->flowlabel);
 	ipv6h->hop_limit = tunnel->parms.hop_limit;
 	ipv6h->nexthdr = proto;
 	ipv6h->saddr = fl6->saddr;
@@ -1240,7 +1238,7 @@ static int ip6gre_header(struct sk_buff *skb, struct net_device *dev,
 	struct ipv6hdr *ipv6h = (struct ipv6hdr *)skb_push(skb, t->hlen);
 	__be16 *p = (__be16 *)(ipv6h+1);
 
-	*(__be32 *)ipv6h = t->fl.u.ip6.flowlabel | htonl(0x60000000);
+	ip6_flow_hdr(ipv6h, 0, t->fl.u.ip6.flowlabel);
 	ipv6h->hop_limit = t->parms.hop_limit;
 	ipv6h->nexthdr = NEXTHDR_GRE;
 	ipv6h->saddr = t->parms.laddr;

net/ipv6/ip6_output.c

@@ -216,7 +216,7 @@ int ip6_xmit(struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 	if (hlimit < 0)
 		hlimit = ip6_dst_hoplimit(dst);
 
-	*(__be32 *)hdr = htonl(0x60000000 | (tclass << 20)) | fl6->flowlabel;
+	ip6_flow_hdr(hdr, tclass, fl6->flowlabel);
 
 	hdr->payload_len = htons(seg_len);
 	hdr->nexthdr = proto;
@@ -267,7 +267,7 @@ int ip6_nd_hdr(struct sock *sk, struct sk_buff *skb, struct net_device *dev,
 	skb_put(skb, sizeof(struct ipv6hdr));
 	hdr = ipv6_hdr(skb);
 
-	*(__be32*)hdr = htonl(0x60000000);
+	ip6_flow_hdr(hdr, 0, 0);
 
 	hdr->payload_len = htons(len);
 	hdr->nexthdr = proto;
@@ -1548,9 +1548,7 @@ int ip6_push_pending_frames(struct sock *sk)
 	skb_reset_network_header(skb);
 	hdr = ipv6_hdr(skb);
 
-	*(__be32*)hdr = fl6->flowlabel |
-		     htonl(0x60000000 | ((int)np->cork.tclass << 20));
-
+	ip6_flow_hdr(hdr, np->cork.tclass, fl6->flowlabel);
 	hdr->hop_limit = np->cork.hop_limit;
 	hdr->nexthdr = proto;
 	hdr->saddr = fl6->saddr;

net/ipv6/ip6_tunnel.c

@@ -1030,9 +1030,7 @@ static int ip6_tnl_xmit2(struct sk_buff *skb,
 	skb_push(skb, sizeof(struct ipv6hdr));
 	skb_reset_network_header(skb);
 	ipv6h = ipv6_hdr(skb);
-	*(__be32*)ipv6h = fl6->flowlabel | htonl(0x60000000);
-	dsfield = INET_ECN_encapsulate(0, dsfield);
-	ipv6_change_dsfield(ipv6h, ~INET_ECN_MASK, dsfield);
+	ip6_flow_hdr(ipv6h, INET_ECN_encapsulate(0, dsfield), fl6->flowlabel);
 	ipv6h->hop_limit = t->parms.hop_limit;
 	ipv6h->nexthdr = proto;
 	ipv6h->saddr = fl6->saddr;

net/ipv6/netfilter/ip6t_REJECT.c

@@ -126,7 +126,7 @@ static void send_reset(struct net *net, struct sk_buff *oldskb)
 	skb_put(nskb, sizeof(struct ipv6hdr));
 	skb_reset_network_header(nskb);
 	ip6h = ipv6_hdr(nskb);
-	*(__be32 *)ip6h =  htonl(0x60000000 | (tclass << 20));
+	ip6_flow_hdr(ip6h, tclass, 0);
 	ip6h->hop_limit = ip6_dst_hoplimit(dst);
 	ip6h->nexthdr = IPPROTO_TCP;
 	ip6h->saddr = oip6h->daddr;