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ipv4: update comment to document GSO fragmentation cases. 

This is a follow-up to commit 9ee6c5dc81 ("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 <shmulik.ladkani@gmail.com>
Reviewed-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lance Richardson 2016-11-09 15:04:39 -05:00 committed by David S. Miller
parent 9b6c14d51b
commit 0ace81ec71
1 changed files with 11 additions and 5 deletions
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16
net/ipv4/ip_output.c
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@ -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);