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net: ipv4: Refine the ipv4_default_advmss 

1. Don't get the metric RTAX_ADVMSS of dst.
There are two reasons.
1) Its caller dst_metric_advmss has already invoke dst_metric_advmss
before invoke default_advmss.
2) The ipv4_default_advmss is used to get the default mss, it should
not try to get the metric like ip6_default_advmss.

2. Use sizeof(tcphdr)+sizeof(iphdr) instead of literal 40.

3. Define one new macro IPV4_MAX_PMTU instead of 65535 according to
RFC 2675, section 5.1.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gao Feng 2017-04-12 12:34:03 +08:00 committed by David S. Miller
parent 29b904a0dd
commit 7ed14d973f
2 changed files with 6 additions and 8 deletions
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2
include/net/ip.h
View File

@ -33,6 +33,8 @@
#include <net/flow.h>
#include <net/flow_dissector.h>
#define IPV4_MAX_PMTU 65535U /* RFC 2675, Section 5.1 */
struct sock;
struct inet_skb_parm {

12
net/ipv4/route.c
View File

@ -1250,15 +1250,11 @@ static void set_class_tag(struct rtable *rt, u32 tag)
static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
{
unsigned int advmss = dst_metric_raw(dst, RTAX_ADVMSS);
unsigned int header_size = sizeof(struct tcphdr) + sizeof(struct iphdr);
unsigned int advmss = max_t(unsigned int, dst->dev->mtu - header_size,
ip_rt_min_advmss);
if (advmss == 0) {
advmss = max_t(unsigned int, dst->dev->mtu - 40,
ip_rt_min_advmss);
if (advmss > 65535 - 40)
advmss = 65535 - 40;
}
return advmss;
return min(advmss, IPV4_MAX_PMTU - header_size);
}
static unsigned int ipv4_mtu(const struct dst_entry *dst)