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Commit 0ace81ec authored by Lance Richardson's avatar Lance Richardson Committed by David S. Miller
Browse files

ipv4: update comment to document GSO fragmentation cases. 



This is a follow-up to commit 9ee6c5dc ("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: default avatarShmulik Ladkani <shmulik.ladkani@gmail.com>
Reviewed-by: default avatarShmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: default avatarLance Richardson <lrichard@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9b6c14d5

net/ipv4/ip_output.c

+11 −5
Original line number Diff line number Diff line
@@ -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);