[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/include/linux/in.h b/include/linux/in.h
index 1912e7c..3975cbf 100644 (file)
--- a/include/linux/in.h
+++ b/include/linux/in.h
@@ -83,6 +83,7 @@ struct in_addr {
 #define IP_PMTUDISC_DONT               0       /* Never send DF frames */
 #define IP_PMTUDISC_WANT               1       /* Use per route hints  */
 #define IP_PMTUDISC_DO                 2       /* Always DF            */
+#define IP_PMTUDISC_PROBE              3       /* Ignore dst pmtu      */
 
 #define IP_MULTICAST_IF                        32
 #define IP_MULTICAST_TTL               33

diff --git a/include/linux/in6.h b/include/linux/in6.h
index 4e8350a..d559fac 100644 (file)
--- a/include/linux/in6.h
+++ b/include/linux/in6.h
@@ -179,6 +179,7 @@ struct in6_flowlabel_req
 #define IPV6_PMTUDISC_DONT             0
 #define IPV6_PMTUDISC_WANT             1
 #define IPV6_PMTUDISC_DO               2
+#define IPV6_PMTUDISC_PROBE            3
 
 /* Flowlabel */
 #define IPV6_FLOWLABEL_MGR     32

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 34606ef..534650c 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -189,6 +189,14 @@ static inline int ip_finish_output2(struct sk_buff *skb)
        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 @@ static inline int ip_finish_output(struct sk_buff *skb)
                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 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff*))
        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 @@ int ip_append_data(struct sock *sk,
                        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 @@ int ip_push_pending_frames(struct sock *sk)
         * 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);

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index c199d23..4d54457 100644 (file)
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -542,7 +542,7 @@ static int do_ip_setsockopt(struct sock *sk, int level,
                inet->hdrincl = val ? 1 : 0;
                break;
        case IP_MTU_DISCOVER:
-               if (val<0 || val>2)
+               if (val<0 || val>3)
                        goto e_inval;
                inet->pmtudisc = val;
                break;

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 5a5b7d4..f508171 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -137,9 +137,17 @@ static int ip6_output2(struct sk_buff *skb)
        return NF_HOOK(PF_INET6, NF_IP6_POST_ROUTING, skb,NULL, skb->dev,ip6_output_finish);
 }
 
+static inline int ip6_skb_dst_mtu(struct sk_buff *skb)
+{
+       struct ipv6_pinfo *np = skb->sk ? inet6_sk(skb->sk) : NULL;
+
+       return (np && np->pmtudisc == IPV6_PMTUDISC_PROBE) ?
+              skb->dst->dev->mtu : dst_mtu(skb->dst);
+}
+
 int ip6_output(struct sk_buff *skb)
 {
-       if ((skb->len > dst_mtu(skb->dst) && !skb_is_gso(skb)) ||
+       if ((skb->len > ip6_skb_dst_mtu(skb) && !skb_is_gso(skb)) ||
                                dst_allfrag(skb->dst))
                return ip6_fragment(skb, ip6_output2);
        else
@@ -566,7 +574,7 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
        hlen = ip6_find_1stfragopt(skb, &prevhdr);
        nexthdr = *prevhdr;
 
-       mtu = dst_mtu(&rt->u.dst);
+       mtu = ip6_skb_dst_mtu(skb);
 
        /* We must not fragment if the socket is set to force MTU discovery
         * or if the skb it not generated by a local socket.  (This last
@@ -1063,7 +1071,8 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
                inet->cork.fl = *fl;
                np->cork.hop_limit = hlimit;
                np->cork.tclass = tclass;
-               mtu = dst_mtu(rt->u.dst.path);
+               mtu = np->pmtudisc == IPV6_PMTUDISC_PROBE ?
+                     rt->u.dst.dev->mtu : dst_mtu(rt->u.dst.path);
                if (np->frag_size < mtu) {
                        if (np->frag_size)
                                mtu = np->frag_size;

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index da930fa..aa3d07c 100644 (file)
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -694,7 +694,7 @@ done:
                retv = ip6_ra_control(sk, val, NULL);
                break;
        case IPV6_MTU_DISCOVER:
-               if (val<0 || val>2)
+               if (val<0 || val>3)
                        goto e_inval;
                np->pmtudisc = val;
                retv = 0;