ipv6: exthdrs: get rid of indirect calls in ip6_parse_tlv()

As presented last month in our "BIG TCP" talk at netdev 0x15,
we plan using IPv6 jumbograms.

One of the minor problem we talked about is the fact that
ip6_parse_tlv() is currently using tables to list known tlvs,
thus using potentially expensive indirect calls.

While we could mitigate this cost using macros from
indirect_call_wrapper.h, we also can get rid of the tables
and let the compiler emit optimized code.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Justin Iurman <justin.iurman@uliege.be>
Cc: Coco Li <lixiaoyan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

net/ipv6/exthdrs.c

@@ -55,19 +55,6 @@
 
 #include <linux/uaccess.h>
 
-/*
- *	Parsing tlv encoded headers.
- *
- *	Parsing function "func" returns true, if parsing succeed
- *	and false, if it failed.
- *	It MUST NOT touch skb->h.
- */
-
-struct tlvtype_proc {
-	int	type;
-	bool	(*func)(struct sk_buff *skb, int offset);
-};
-
 /*********************
   Generic functions
  *********************/
@@ -112,16 +99,23 @@ static bool ip6_tlvopt_unknown(struct sk_buff *skb, int optoff,
 	return false;
 }
 
+static bool ipv6_hop_ra(struct sk_buff *skb, int optoff);
+static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff);
+static bool ipv6_hop_jumbo(struct sk_buff *skb, int optoff);
+static bool ipv6_hop_calipso(struct sk_buff *skb, int optoff);
+#if IS_ENABLED(CONFIG_IPV6_MIP6)
+static bool ipv6_dest_hao(struct sk_buff *skb, int optoff);
+#endif
+
 /* Parse tlv encoded option header (hop-by-hop or destination) */
 
-static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
+static bool ip6_parse_tlv(bool hopbyhop,
 			  struct sk_buff *skb,
 			  int max_count)
 {
 	int len = (skb_transport_header(skb)[1] + 1) << 3;
 	const unsigned char *nh = skb_network_header(skb);
 	int off = skb_network_header_len(skb);
-	const struct tlvtype_proc *curr;
 	bool disallow_unknowns = false;
 	int tlv_count = 0;
 	int padlen = 0;
@@ -176,20 +170,45 @@ static bool ip6_parse_tlv(const struct tlvtype_proc *procs,
 			if (tlv_count > max_count)
 				goto bad;
 
-			for (curr = procs; curr->type >= 0; curr++) {
-				if (curr->type == nh[off]) {
-					/* type specific length/alignment
-					   checks will be performed in the
-					   func(). */
-					if (curr->func(skb, off) == false)
+			if (hopbyhop) {
+				switch (nh[off]) {
+				case IPV6_TLV_ROUTERALERT:
+					if (!ipv6_hop_ra(skb, off))
+						return false;
+					break;
+				case IPV6_TLV_IOAM:
+					if (!ipv6_hop_ioam(skb, off))
+						return false;
+					break;
+				case IPV6_TLV_JUMBO:
+					if (!ipv6_hop_jumbo(skb, off))
+						return false;
+					break;
+				case IPV6_TLV_CALIPSO:
+					if (!ipv6_hop_calipso(skb, off))
+						return false;
+					break;
+				default:
+					if (!ip6_tlvopt_unknown(skb, off,
+								disallow_unknowns))
+						return false;
+					break;
+				}
+			} else {
+				switch (nh[off]) {
+#if IS_ENABLED(CONFIG_IPV6_MIP6)
+				case IPV6_TLV_HAO:
+					if (!ipv6_dest_hao(skb, off))
+						return false;
+					break;
+#endif
+				default:
+					if (!ip6_tlvopt_unknown(skb, off,
+								disallow_unknowns))
 						return false;
 					break;
 				}
 			}
-			if (curr->type < 0 &&
-			    !ip6_tlvopt_unknown(skb, off, disallow_unknowns))
-				return false;
-
 			padlen = 0;
 		}
 		off += optlen;
@@ -267,16 +286,6 @@ static bool ipv6_dest_hao(struct sk_buff *skb, int optoff)
 }
 #endif
 
-static const struct tlvtype_proc tlvprocdestopt_lst[] = {
-#if IS_ENABLED(CONFIG_IPV6_MIP6)
-	{
-		.type	= IPV6_TLV_HAO,
-		.func	= ipv6_dest_hao,
-	},
-#endif
-	{-1,			NULL}
-};
-
 static int ipv6_destopt_rcv(struct sk_buff *skb)
 {
 	struct inet6_dev *idev = __in6_dev_get(skb->dev);
@@ -307,8 +316,7 @@ static int ipv6_destopt_rcv(struct sk_buff *skb)
 	dstbuf = opt->dst1;
 #endif
 
-	if (ip6_parse_tlv(tlvprocdestopt_lst, skb,
-			  net->ipv6.sysctl.max_dst_opts_cnt)) {
+	if (ip6_parse_tlv(false, skb, net->ipv6.sysctl.max_dst_opts_cnt)) {
 		skb->transport_header += extlen;
 		opt = IP6CB(skb);
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
@@ -1051,26 +1059,6 @@ static bool ipv6_hop_calipso(struct sk_buff *skb, int optoff)
 	return false;
 }
 
-static const struct tlvtype_proc tlvprochopopt_lst[] = {
-	{
-		.type	= IPV6_TLV_ROUTERALERT,
-		.func	= ipv6_hop_ra,
-	},
-	{
-		.type	= IPV6_TLV_IOAM,
-		.func	= ipv6_hop_ioam,
-	},
-	{
-		.type	= IPV6_TLV_JUMBO,
-		.func	= ipv6_hop_jumbo,
-	},
-	{
-		.type	= IPV6_TLV_CALIPSO,
-		.func	= ipv6_hop_calipso,
-	},
-	{ -1, }
-};
-
 int ipv6_parse_hopopts(struct sk_buff *skb)
 {
 	struct inet6_skb_parm *opt = IP6CB(skb);
@@ -1096,8 +1084,7 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
 		goto fail_and_free;
 
 	opt->flags |= IP6SKB_HOPBYHOP;
-	if (ip6_parse_tlv(tlvprochopopt_lst, skb,
-			  net->ipv6.sysctl.max_hbh_opts_cnt)) {
+	if (ip6_parse_tlv(true, skb, net->ipv6.sysctl.max_hbh_opts_cnt)) {
 		skb->transport_header += extlen;
 		opt = IP6CB(skb);
 		opt->nhoff = sizeof(struct ipv6hdr);