Re: [PATCH net-next 08/15] ipv6: Add hop-by-hop header to jumbograms in ip6_output

From: Coco Li <redacted>

Instead of simply forcing a 0 payload_len in IPv6 header,
implement RFC 2675 and insert a custom extension header.

Note that only TCP stack is currently potentially generating
jumbograms, and that this extension header is purely local,
it wont be sent on a physical link.

This is needed so that packet capture (tcpdump and friends)
can properly dissect these large packets.

Signed-off-by: Coco Li <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/ipv6.h  |  1 +
 net/ipv6/ip6_output.c | 22 ++++++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 1e0f8a31f3de175659dca9ecee9f97d8b01e2b68..d3fb87e1589997570cde9cb5d92b2222008a229d 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h

@@ -144,6 +144,7 @@ struct inet6_skb_parm {
 #define IP6SKB_L3SLAVE         64
 #define IP6SKB_JUMBOGRAM      128
 #define IP6SKB_SEG6	      256
+#define IP6SKB_FAKEJUMBO      512
 };
 
 #if defined(CONFIG_NET_L3_MASTER_DEV)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 0c6c971ce0a58b50f8a9349b8507dffac9c7818c..f78ba145620560e5d7cb25aaf16fec61ddd9ed40 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c

@@ -180,7 +180,9 @@ static int __ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff
 #endif
 
 	mtu = ip6_skb_dst_mtu(skb);
-	if (skb_is_gso(skb) && !skb_gso_validate_network_len(skb, mtu))
+	if (skb_is_gso(skb) &&
+	    !(IP6CB(skb)->flags & IP6SKB_FAKEJUMBO) &&
+	    !skb_gso_validate_network_len(skb, mtu))
 		return ip6_finish_output_gso_slowpath_drop(net, sk, skb, mtu);