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 <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>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9403fa3..105908d 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -244,12 +244,18 @@
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);