netdev - [PATCH 5/5] soreuseport: UDP/IPv6 implementation

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Date:	Mon, 14 Jan 2013 12:00:26 -0800 (PST)
From:	Tom Herbert <therbert@...gle.com>
To:	netdev@...r.kernel.org, davem@...emloft.net
cc:	netdev@...kandruth.co.uk, eric.dumazet@...il.com
Subject: [PATCH 5/5] soreuseport: UDP/IPv6 implementation

Allow multiple UDP sockets to bind to the same port.

Motivation for soreuseport would be something like a DNS server.  An
alternative would be to recv on the same socket from multiple threads.
As in the case of TCP, the load across these threads tends to be
disproportionate and we also see a lot of contection on the socket lock.
Note that SO_REUSEADDR already allows multiple UDP sockets to bind to
the same port, however there is no provision to prevent hijacking and
nothing to distribute packets across all the sockets sharing the same
bound port.  This patch does not change the semantics of SO_REUSEADDR,
but provides usable functionality of it for unicast.

Signed-off-by: Tom Herbert <therbert@...gle.com>
---
 net/ipv6/udp.c |   30 +++++++++++++++++++++++++++---
 1 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 1afb635..779d8c0 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -45,6 +45,7 @@
 #include <net/tcp_states.h>
 #include <net/ip6_checksum.h>
 #include <net/xfrm.h>
+#include <net/inet6_hashtables.h>
 
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
@@ -203,7 +204,8 @@ static struct sock *udp6_lib_lookup2(struct net *net,
 {
 	struct sock *sk, *result;
 	struct hlist_nulls_node *node;
-	int score, badness;
+	int score, badness, matches = 0, reuseport = 0;
+	u32 hash = 0;
 
 begin:
 	result = NULL;
@@ -214,8 +216,18 @@ begin:
 		if (score > badness) {
 			result = sk;
 			badness = score;
-			if (score == SCORE2_MAX)
+			reuseport = sk->sk_reuseport;
+			if (reuseport) {
+				hash = inet6_ehashfn(net, daddr, hnum,
+				    saddr, sport);
+				matches = 1;
+			} else if (score == SCORE2_MAX)
 				goto exact_match;
+		} else if (score == badness && reuseport) {
+			matches++;
+			if (((u64)hash * matches) >> 32 == 0)
+				result = sk;
+			hash = next_pseudo_random32(hash);
 		}
 	}
 	/*
@@ -249,7 +261,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
 	unsigned short hnum = ntohs(dport);
 	unsigned int hash2, slot2, slot = udp_hashfn(net, hnum, udptable->mask);
 	struct udp_hslot *hslot2, *hslot = &udptable->hash[slot];
-	int score, badness;
+	int score, badness, matches = 0, reuseport = 0;
+	u32 hash = 0;
 
 	rcu_read_lock();
 	if (hslot->count > 10) {
@@ -284,6 +297,17 @@ begin:
 		if (score > badness) {
 			result = sk;
 			badness = score;
+			reuseport = sk->sk_reuseport;
+			if (reuseport) {
+				hash = inet6_ehashfn(net, daddr, hnum,
+				    saddr, sport);
+				matches = 1;
+			}
+		} else if (score == badness && reuseport) {
+			matches++;
+			if (((u64)hash * matches) >> 32 == 0)
+				result = sk;
+			hash = next_pseudo_random32(hash);
 		}
 	}
 	/*
-- 
1.7.7.3