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 |   35 +++++++++++++++++++++++++++++++++++
 1 files changed, 35 insertions(+), 0 deletions(-)

index b557ec4..1251603 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>
 @@ -752,6 +759,34 @@ static int vnet_start_xmit(struct sk_buff *skb, struct net_device *dev)

goto out_dropped;
if (skb->len > port->vio.rmtu) {
+ unsigned long localmtu = port->vio.rmtu - ETH_HLEN;
+
+ if (port->vio.ver.major == 1 && port->vio.ver.minor >= 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;
}
-- 1.7.1

From: David L Stevens <[email protected]>
Date: Fri, 12 Sep 2014 18:22:52 -0400

Hello.

Yes, it was mangled by my mailer. I think PATCHv3, the latest I sent, is ok, but please try that. And, of course, let me know if it doesn't work.

						+-DLS