[INET]: Add IP(V6)_PMTUDISC_RPOBE
Add IP(V6)_PMTUDISC_PROBE value for IP(V6)_MTU_DISCOVER. This option forces
us not to fragment, but does not make use of the kernel path MTU discovery.
That is, it allows for user-mode MTU probing (or, packetization-layer path
MTU discovery). This is particularly useful for diagnostic utilities, like
traceroute/tracepath.
Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 34606ef..534650c 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -189,6 +189,14 @@
return -EINVAL;
}
+static inline int ip_skb_dst_mtu(struct sk_buff *skb)
+{
+ struct inet_sock *inet = skb->sk ? inet_sk(skb->sk) : NULL;
+
+ return (inet && inet->pmtudisc == IP_PMTUDISC_PROBE) ?
+ skb->dst->dev->mtu : dst_mtu(skb->dst);
+}
+
static inline int ip_finish_output(struct sk_buff *skb)
{
#if defined(CONFIG_NETFILTER) && defined(CONFIG_XFRM)
@@ -198,7 +206,7 @@
return dst_output(skb);
}
#endif
- if (skb->len > dst_mtu(skb->dst) && !skb_is_gso(skb))
+ if (skb->len > ip_skb_dst_mtu(skb) && !skb_is_gso(skb))
return ip_fragment(skb, ip_finish_output2);
else
return ip_finish_output2(skb);
@@ -422,7 +430,7 @@
if (unlikely((iph->frag_off & htons(IP_DF)) && !skb->local_df)) {
IP_INC_STATS(IPSTATS_MIB_FRAGFAILS);
icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
- htonl(dst_mtu(&rt->u.dst)));
+ htonl(ip_skb_dst_mtu(skb)));
kfree_skb(skb);
return -EMSGSIZE;
}
@@ -787,7 +795,9 @@
inet->cork.addr = ipc->addr;
}
dst_hold(&rt->u.dst);
- inet->cork.fragsize = mtu = dst_mtu(rt->u.dst.path);
+ inet->cork.fragsize = mtu = inet->pmtudisc == IP_PMTUDISC_PROBE ?
+ rt->u.dst.dev->mtu :
+ dst_mtu(rt->u.dst.path);
inet->cork.rt = rt;
inet->cork.length = 0;
sk->sk_sndmsg_page = NULL;
@@ -1203,13 +1213,13 @@
* to fragment the frame generated here. No matter, what transforms
* how transforms change size of the packet, it will come out.
*/
- if (inet->pmtudisc != IP_PMTUDISC_DO)
+ if (inet->pmtudisc < IP_PMTUDISC_DO)
skb->local_df = 1;
/* DF bit is set when we want to see DF on outgoing frames.
* If local_df is set too, we still allow to fragment this frame
* locally. */
- if (inet->pmtudisc == IP_PMTUDISC_DO ||
+ if (inet->pmtudisc >= IP_PMTUDISC_DO ||
(skb->len <= dst_mtu(&rt->u.dst) &&
ip_dont_fragment(sk, &rt->u.dst)))
df = htons(IP_DF);