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>
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 5e1e605..0fcc2d5 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -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)