[PATCH net-next 2/4] flow_dissector: skip the ICMP dissector for non ICMP packets

[Matteo Croce]

FLOW_DISSECTOR_KEY_ICMP is checked for every packet, not only ICMP ones.
Even if the test overhead is probably negligible, move the
ICMP dissector code under the big 'switch(ip_proto)' so it gets called
only for ICMP packets.

Signed-off-by: Matteo Croce <mcr...@redhat.com>
---
 net/core/flow_dissector.c | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index affde70dad47..6443fac65ce8 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -203,6 +203,25 @@ __be32 __skb_flow_get_ports(const struct sk_buff *skb, int 
thoff, u8 ip_proto,
 }
 EXPORT_SYMBOL(__skb_flow_get_ports);
 
+/* If FLOW_DISSECTOR_KEY_ICMP is set, get the Type and Code from an ICMP packet
+ * using skb_flow_get_be16().
+ */
+static void __skb_flow_dissect_icmp(const struct sk_buff *skb,
+                                   struct flow_dissector *flow_dissector,
+                                   void *target_container,
+                                   void *data, int thoff, int hlen)
+{
+       struct flow_dissector_key_icmp *key_icmp;
+
+       if (!dissector_uses_key(flow_dissector, FLOW_DISSECTOR_KEY_ICMP))
+               return;
+
+       key_icmp = skb_flow_dissector_target(flow_dissector,
+                                            FLOW_DISSECTOR_KEY_ICMP,
+                                            target_container);
+       key_icmp->icmp = skb_flow_get_be16(skb, thoff, data, hlen);
+}
+
 void skb_flow_dissect_meta(const struct sk_buff *skb,
                           struct flow_dissector *flow_dissector,
                           void *target_container)
@@ -853,7 +872,6 @@ bool __skb_flow_dissect(const struct net *net,
        struct flow_dissector_key_basic *key_basic;
        struct flow_dissector_key_addrs *key_addrs;
        struct flow_dissector_key_ports *key_ports;
-       struct flow_dissector_key_icmp *key_icmp;
        struct flow_dissector_key_tags *key_tags;
        struct flow_dissector_key_vlan *key_vlan;
        struct bpf_prog *attached = NULL;
@@ -1295,6 +1313,12 @@ bool __skb_flow_dissect(const struct net *net,
                                       data, nhoff, hlen);
                break;
 
+       case IPPROTO_ICMP:
+       case IPPROTO_ICMPV6:
+               __skb_flow_dissect_icmp(skb, flow_dissector, target_container,
+                                       data, nhoff, hlen);
+               break;
+
        default:
                break;
        }
@@ -1308,14 +1332,6 @@ bool __skb_flow_dissect(const struct net *net,
                                                        data, hlen);
        }
 
-       if (dissector_uses_key(flow_dissector,
-                              FLOW_DISSECTOR_KEY_ICMP)) {
-               key_icmp = skb_flow_dissector_target(flow_dissector,
-                                                    FLOW_DISSECTOR_KEY_ICMP,
-                                                    target_container);
-               key_icmp->icmp = skb_flow_get_be16(skb, nhoff, data, hlen);
-       }
-
        /* Process result of IP proto processing */
        switch (fdret) {
        case FLOW_DISSECT_RET_PROTO_AGAIN:
-- 
2.21.0