From 0ace81ec7192201af48528c309ee0b4103021f55 Mon Sep 17 00:00:00 2001 From: Lance Richardson Date: Wed, 9 Nov 2016 15:04:39 -0500 Subject: [PATCH] ipv4: update comment to document GSO fragmentation cases. This is a follow-up to commit 9ee6c5dc816a ("ipv4: allow local fragmentation in ip_finish_output_gso()"), updating the comment documenting cases in which fragmentation is needed for egress GSO packets. Suggested-by: Shmulik Ladkani Reviewed-by: Shmulik Ladkani Signed-off-by: Lance Richardson Signed-off-by: David S. Miller --- net/ipv4/ip_output.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index 9403fa3850be..105908d841a3 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -244,12 +244,18 @@ static int ip_finish_output_gso(struct net *net, struct sock *sk, if (skb_gso_validate_mtu(skb, mtu)) return ip_finish_output2(net, sk, skb); - /* Slowpath - GSO segment length is exceeding the dst MTU. + /* Slowpath - GSO segment length exceeds the egress MTU. * - * This can happen in two cases: - * 1) TCP GRO packet, DF bit not set - * 2) skb arrived via virtio-net, we thus get TSO/GSO skbs directly - * from host network stack. + * This can happen in several cases: + * - Forwarding of a TCP GRO skb, when DF flag is not set. + * - Forwarding of an skb that arrived on a virtualization interface + * (virtio-net/vhost/tap) with TSO/GSO size set by other network + * stack. + * - Local GSO skb transmitted on an NETIF_F_TSO tunnel stacked over an + * interface with a smaller MTU. + * - Arriving GRO skb (or GSO skb in a virtualized environment) that is + * bridged to a NETIF_F_TSO tunnel stacked over an interface with an + * insufficent MTU. */ features = netif_skb_features(skb); BUILD_BUG_ON(sizeof(*IPCB(skb)) > SKB_SGO_CB_OFFSET); -- 2.20.1