Re: [PATCH net-next 1/4] net/flow_dissector: add support for dissection of misc ip header fields

On Thu, May 25, 2017 at 7:22 PM, Tom Herbert [off-list ref] wrote:

On Thu, May 25, 2017 at 6:24 AM, Or Gerlitz [off-list ref] wrote:

quoted

Add support for dissection of ip tos and ttl and ipv6 traffic-class
and hoplimit. Both are dissected into the same struct.

quoted

Uses similar call to ip dissection function as with tcp, arp and others.

quoted

+/**
+ * struct flow_dissector_key_ip:
+ * @tos: tos
+ * @ttl: ttl
+ */
+struct flow_dissector_key_ip {
+       __u8    tos;
+       __u8    ttl;
+};

--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c

quoted

+static void
+__skb_flow_dissect_ipv4(const struct sk_buff *skb,
+                       struct flow_dissector *flow_dissector,
+                       void *target_container, void *data, const struct iphdr *iph)
+{
+       struct flow_dissector_key_ip *key_ip;
+
+       if (!dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_IP))
+               return;
+
+       key_ip = skb_flow_dissector_target(flow_dissector,
+                                          FLOW_DISSECTOR_KEY_IP,
+                                          target_container);
+       key_ip->tos = iph->tos;
+       key_ip->ttl = iph->ttl;

In an encapsulation this returns the tos and ttl of the encapsulated
packet. Is that really useful to the caller? Seems more likely that
they need the outer tos and ttl for forwarding.

In what we are dealing with, classification is carried after the
packet is decapsulated by the shared tunnel device. So even today,e.g
for the src/dst IP, the dissection is carried on what were the inner
fields before decap.

When we did the the flower patches for being able to classify on both
the inner and outer fields (say outer src/dst ip, tunnel key) for what
related to the  macs/ips/ports/etc -- I don't think we touched the
existing dissection, I will look on that to see if I am wrong..