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ipv6: add IPV6_RECVFRAGSIZE cmsg

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When reading a datagram or raw packet that arrived fragmented, expose
the maximum fragment size if recorded to allow applications to
estimate receive path MTU.

At this point, the field is only recorded when ipv6 connection
tracking is enabled. A follow-up patch will record this field also
in the ipv6 input path.

Tested using the test for IP_RECVFRAGSIZE plus

  ip netns exec to ip addr add dev veth1 fc07::1/64
  ip netns exec from ip addr add dev veth0 fc07::2/64

  ip netns exec to ./recv_cmsg_recvfragsize -6 -u -p 6000 &
  ip netns exec from nc -q 1 -u fc07::1 6000 < payload

Both with and without enabling connection tracking

  ip6tables -A INPUT -m state --state NEW -p udp -j LOG

Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn
2016-11-02 11:02:17 -04:00
committed by David S. Miller
parent 70ecc24841
commit 0cc0aa614b
4 changed files with 17 additions and 2 deletions
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1
include/uapi/linux/in6.h
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@@ -283,6 +283,7 @@ struct in6_flowlabel_req {
#define IPV6_RECVORIGDSTADDR IPV6_ORIGDSTADDR
#define IPV6_TRANSPARENT 75
#define IPV6_UNICAST_IF 76
#define IPV6_RECVFRAGSIZE 77
/*
* Multicast Routing: