sunvnet: generate ICMP PTMUD messages for smaller port MTUs

This patch sends ICMP and ICMPv6 messages for Path MTU Discovery when a remote port MTU is smaller than the device MTU. This allows mixing newer VIO protocol devices that support MTU negotiation with older devices that do not on the same vswitch. It also allows Linux-Linux LDOMs to use 64K-1 data packets even though Solaris vswitch is limited to <16K MTU.

---
 drivers/net/ethernet/sun/sunvnet.c |   37 +++++++++++++++++++++++++++++++++++-
 1 files changed, 36 insertions(+), 1 deletions(-)

index 1a7dce0..cb2d2b7 100644
@@ -17,6 +17,13 @@
 #include <linux/mutex.h>
 #include <linux/if_vlan.h>
 +#if IS_ENABLED(CONFIG_IPV6)
+#include <linux/icmpv6.h>
+#endif
+
+#include <net/icmp.h>
+#include <net/route.h>
+
 #include <asm/vio.h>
 #include <asm/ldc.h>
 @@ -884,8 +891,36 @@ static int vnet_start_xmit(struct sk_buff *skb, struct net_device *dev)

skb = vnet_skb_shape(skb, &start, &nlen);
- if (skb->len > port->rmtu)
+ if (skb->len > port->rmtu) {
+ unsigned long localmtu = port->rmtu - ETH_HLEN;
+
+ if (vio_version_after_eq(&port->vio, 1, 3))
+ localmtu -= VLAN_HLEN;
+
+ if (skb->protocol == htons(ETH_P_IP)) {
+ struct flowi4 fl4;
+ struct rtable *rt = NULL;
+
+ memset(&fl4, 0, sizeof(fl4));
+ fl4.flowi4_oif = dev->ifindex;
+ fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
+ fl4.daddr = ip_hdr(skb)->daddr;
+ fl4.saddr = ip_hdr(skb)->saddr;
+
+ rt = ip_route_output_key(dev_net(dev), &fl4);
+ if (!IS_ERR(rt)) {
+ skb_dst_set(skb, &rt->dst);
+ icmp_send(skb, ICMP_DEST_UNREACH,
+ ICMP_FRAG_NEEDED,
+ htonl(localmtu));
+ }
+ }
+#if IS_ENABLED(CONFIG_IPV6)
+ else if (skb->protocol == htons(ETH_P_IPV6))
+ icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, localmtu);
+#endif
goto out_dropped;
+ }
spin_lock_irqsave(&port->vio.lock, flags);
-- 1.7.1