netdev - Re: [RFC bpf-next v2 2/9] net: introduce skb

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Date:   Tue, 19 Mar 2019 22:14:35 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Network Development <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        simon.horman@...ronome.com, Willem de Bruijn <willemb@...gle.com>,
        Petar Penkov <peterpenkov96@...il.com>
Subject: Re: [RFC bpf-next v2 2/9] net: introduce skb_net helper

On Tue, Mar 19, 2019 at 6:20 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> skb_net returns network namespace from the associated device or socket.
>
> This will be used in the next commit.
>
> I tried to inline it in skbuff.h, but I don't think it's feasible.

If so, is this helper necessary?

All existing cases that use it pass both skb_net(skb) and skb to the
flow dissector, so can continue to call it locally if new argument net
is NULL.

The new users are in patch 9/9 in the device drivers, but those should
pass the device pointer unconditionally.



> It depends on 'net/sock.h' for sock_net() and 'linux/netdevice.h' for
> dev_net(), both of which we don't include from 'linux/skbuff.h' (but
> both sock.h and netdevice.h include skbuff.h). I though about doing
> it as a macro/putting it somewhere else, but we will have
> skb_flow_dissect{_xyz} use it in the next commits.
>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>  include/linux/skbuff.h |  2 ++
>  net/core/skbuff.c      | 16 ++++++++++++++++
>  2 files changed, 18 insertions(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index e8c1d5b97f96..75e1d4d73cca 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1275,6 +1275,8 @@ static inline int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
>  }
>  #endif
>
> +struct net *skb_net(const struct sk_buff *skb);
> +
>  struct bpf_flow_keys;
>  bool __skb_flow_bpf_dissect(struct bpf_prog *prog,
>                             const struct sk_buff *skb,
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index b413354ee709..d81f3a95fb4e 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -5725,3 +5725,19 @@ void __skb_ext_put(struct skb_ext *ext)
>  }
>  EXPORT_SYMBOL(__skb_ext_put);
>  #endif /* CONFIG_SKB_EXTENSIONS */
> +
> +/**
> + * skb_net - Return network namespace associated with skb.
> + * @skb: skb
> + *
> + * Returns pointer to struct net or NULL.
> + */
> +struct net *skb_net(const struct sk_buff *skb)
> +{
> +       if (skb->dev)
> +               return dev_net(skb->dev);
> +       else if (skb->sk)
> +               return sock_net(skb->sk);
> +       return NULL;
> +}
> +EXPORT_SYMBOL(skb_net);
> --
> 2.21.0.225.g810b269d1ac-goog
>