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

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Date:   Thu, 25 May 2017 09:22:57 -0700
From:   Tom Herbert <tom@...bertland.com>
To:     Or Gerlitz <ogerlitz@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Roi Dayan <roid@...lanox.com>, Paul Blakey <paulb@...lanox.com>
Subject: Re: [PATCH net-next 1/4] net/flow_dissector: add support for
 dissection of misc ip header fields

On Thu, May 25, 2017 at 6:24 AM, Or Gerlitz <ogerlitz@...lanox.com> wrote:
> Add support for dissection of ip tos and ttl and ipv6 traffic-class
> and hoplimit. Both are dissected into the same struct.
>
> Uses similar call to ip dissection function as with tcp, arp and others.
>
> Signed-off-by: Or Gerlitz <ogerlitz@...lanox.com>
> Reviewed-by: Jiri Pirko <jiri@...lanox.com>
> ---
>  include/net/flow_dissector.h | 11 +++++++++++
>  net/core/flow_dissector.c    | 40 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 51 insertions(+)
>
> diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
> index efe34eec..e2663e9 100644
> --- a/include/net/flow_dissector.h
> +++ b/include/net/flow_dissector.h
> @@ -165,6 +165,16 @@ struct flow_dissector_key_tcp {
>         __be16 flags;
>  };
>
> +/**
> + * struct flow_dissector_key_ip:
> + * @tos: tos
> + * @ttl: ttl
> + */
> +struct flow_dissector_key_ip {
> +       __u8    tos;
> +       __u8    ttl;
> +};
> +
>  enum flow_dissector_key_id {
>         FLOW_DISSECTOR_KEY_CONTROL, /* struct flow_dissector_key_control */
>         FLOW_DISSECTOR_KEY_BASIC, /* struct flow_dissector_key_basic */
> @@ -186,6 +196,7 @@ enum flow_dissector_key_id {
>         FLOW_DISSECTOR_KEY_ENC_PORTS, /* struct flow_dissector_key_ports */
>         FLOW_DISSECTOR_KEY_MPLS, /* struct flow_dissector_key_mpls */
>         FLOW_DISSECTOR_KEY_TCP, /* struct flow_dissector_key_tcp */
> +       FLOW_DISSECTOR_KEY_IP, /* struct flow_dissector_key_ip */
>
>         FLOW_DISSECTOR_KEY_MAX,
>  };
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 5a45943..fc5fc45 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -367,6 +367,40 @@ __skb_flow_dissect_tcp(const struct sk_buff *skb,
>         key_tcp->flags = (*(__be16 *) &tcp_flag_word(th) & htons(0x0FFF));
>  }
>
> +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.

> +}
> +
> +static void
> +__skb_flow_dissect_ipv6(const struct sk_buff *skb,
> +                       struct flow_dissector *flow_dissector,
> +                       void *target_container, void *data, const struct ipv6hdr *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 = ipv6_get_dsfield(iph);
> +       key_ip->ttl = iph->hop_limit;
> +}
> +
>  /**
>   * __skb_flow_dissect - extract the flow_keys struct and return it
>   * @skb: sk_buff to extract the flow from, can be NULL if the rest are specified
> @@ -469,6 +503,9 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>                         }
>                 }
>
> +               __skb_flow_dissect_ipv4(skb, flow_dissector,
> +                                       target_container, data, iph);
> +
>                 if (flags & FLOW_DISSECTOR_F_STOP_AT_L3)
>                         goto out_good;
>
> @@ -514,6 +551,9 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
>                                 goto out_good;
>                 }
>
> +               __skb_flow_dissect_ipv6(skb, flow_dissector,
> +                                       target_container, data, iph);
> +
>                 if (flags & FLOW_DISSECTOR_F_STOP_AT_L3)
>                         goto out_good;
>
> --
> 2.3.7
>