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

[Simon Horman]

On Mon, Oct 21, 2019 at 10:09:46PM +0200, Matteo Croce wrote:
> 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 <mcroce@xxxxxxxxxx>

Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxxx>

> ---
>  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
>