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udp: intoduce udp_encap_needed static_key 

Most machines dont use UDP encapsulation (L2TP)

Adds a static_key so that udp_queue_rcv_skb() doesnt have to perform a
test if L2TP never setup the encap_rcv on a socket.

Idea of this patch came after Simon Horman proposal to add a hook on TCP
as well.

If static_key is not yet enabled, the fast path does a single JMP .

When static_key is enabled, JMP destination is patched to reach the real
encap_type/encap_rcv logic, possibly adding cache misses.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Simon Horman <horms@verge.net.au>
Cc: dev@openvswitch.org
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-04-11 23:05:28 +00:00 committed by David S. Miller
parent 77577bf932
commit 447167bf56
3 changed files with 13 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/udp.h
View File

@ -267,4 +267,5 @@ extern void udp_init(void);
extern int udp4_ufo_send_check(struct sk_buff *skb);
extern struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
netdev_features_t features);
extern void udp_encap_enable(void);
#endif /* _UDP_H */

12
net/ipv4/udp.c
View File

@ -107,6 +107,7 @@
#include <net/checksum.h>
#include <net/xfrm.h>
#include <trace/events/udp.h>
#include <linux/static_key.h>
#include "udp_impl.h"
struct udp_table udp_table __read_mostly;
@ -1379,6 +1380,14 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
}
static struct static_key udp_encap_needed __read_mostly;
void udp_encap_enable(void)
{
if (!static_key_enabled(&udp_encap_needed))
static_key_slow_inc(&udp_encap_needed);
}
EXPORT_SYMBOL(udp_encap_enable);
/* returns:
* -1: error
* 0: success
@ -1400,7 +1409,7 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
goto drop;
nf_reset(skb);
if (up->encap_type) {
if (static_key_false(&udp_encap_needed) && up->encap_type) {
int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
/*
@ -1760,6 +1769,7 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
/* FALLTHROUGH */
case UDP_ENCAP_L2TPINUDP:
up->encap_type = val;
udp_encap_enable();
break;
default:
err = -ENOPROTOOPT;

1
net/l2tp/l2tp_core.c
View File

@ -1424,6 +1424,7 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
/* Mark socket as an encapsulation socket. See net/ipv4/udp.c */
udp_sk(sk)->encap_type = UDP_ENCAP_L2TPINUDP;
udp_sk(sk)->encap_rcv = l2tp_udp_encap_recv;
udp_encap_enable();
}
sk->sk_user_data = tunnel;