netdev - Re: [Patch bpf-next v7 4/9] skmsg: move sk_redir from TCP_SKB

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Message-ID: <CAM_iQpUCsoXLJ_8BFywJQXmEAXA-Kmes0x7vCN2hnxtoiVaDoQ@mail.gmail.com>
Date:   Mon, 1 Mar 2021 10:24:12 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        duanxiongchun@...edance.com,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf-next v7 4/9] skmsg: move sk_redir from TCP_SKB_CB to skb

On Mon, Mar 1, 2021 at 7:24 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> On Tue, 23 Feb 2021 at 18:49, Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
> > does not work for any other non-TCP protocols. We can move them to
> > skb ext, but it introduces a memory allocation on fast path.
> >
> > Fortunately, we only need to a word-size to store all the information,
> > because the flags actually only contains 1 bit so can be just packed
> > into the lowest bit of the "pointer", which is stored as unsigned
> > long.
> >
> > Inside struct sk_buff, '_skb_refdst' can be reused because skb dst is
> > no longer needed after ->sk_data_ready() so we can just drop it.
>
> Hi Cong Wang,
>
> I saw this on patchwork:
>
> include/linux/skbuff.h:932: warning: Function parameter or member
> '_sk_redir' not described in 'sk_buff'
> New warnings added
> 0a1
> > include/linux/skbuff.h:932: warning: Function parameter or member '_sk_redir' not described in 'sk_buff'
> Per-file breakdown

Ah, I didn't know the function doc is mandatory now.

>
> Source: https://patchwork.kernel.org/project/netdevbpf/patch/20210223184934.6054-5-xiyou.wangcong@gmail.com/
>
> Maybe something to follow up on, I'm not sure what the conventions are here.

It is already merged, so we definitely need a one-line followup fix.

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index bd84f799c952..0503c917d773 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -656,6 +656,7 @@ typedef unsigned char *sk_buff_data_t;
  *     @protocol: Packet protocol from driver
  *     @destructor: Destruct function
  *     @tcp_tsorted_anchor: list structure for TCP (tp->tsorted_sent_queue)
+ *     @_sk_redir: socket redirection information for skmsg
  *     @_nfct: Associated connection, if any (with nfctinfo bits)
  *     @nf_bridge: Saved data about a bridged frame - see br_netfilter.c
  *     @skb_iif: ifindex of device we arrived on

Thanks.