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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ipv6.h

···
 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

···
 	 *	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;
···
 	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

···
 	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;
···
 	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;
···
 	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

···
 	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

···
 	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;