netdev - Re: [RFC PATCH v6 net-next 2/4] tcp: refactor struct tcp_skb

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Date:	Thu, 27 Aug 2015 14:53:17 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Lawrence Brakmo <brakmo@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Kenneth Klette Jonassen <kennetkl@....uio.no>
Subject: Re: [RFC PATCH v6 net-next 2/4] tcp: refactor struct tcp_skb_cb

On Tue, Aug 25, 2015 at 4:33 PM, Lawrence Brakmo <brakmo@...com> wrote:
>
> Refactor tcp_skb_cb to create two overlaping areas to store
> state for incoming or outgoing skbs based on comments by
> Neal Cardwell to tcp_nv patch:
>
>    AFAICT this patch would not require an increase in the size of
>    sk_buff cb[] if it were to take advantage of the fact that the
>    tcp_skb_cb header.h4 and header.h6 fields are only used in the packet
>    reception code path, and this in_flight field is only used on the
>    transmit side.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>

> ---
>  include/net/tcp.h | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 0121529..a086a98 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -755,11 +755,16 @@ struct tcp_skb_cb {
>         /* 1 byte hole */
>         __u32           ack_seq;        /* Sequence number ACK'd        */
>         union {
> -               struct inet_skb_parm    h4;
> +               struct {
> +                       /* There is space for up to 20 bytes */
> +               } tx;   /* only used for outgoing skbs */
> +               union {
> +                       struct inet_skb_parm    h4;
>  #if IS_ENABLED(CONFIG_IPV6)
> -               struct inet6_skb_parm   h6;
> +                       struct inet6_skb_parm   h6;
>  #endif
> -       } header;       /* For incoming frames          */
> +               } header;       /* For incoming skbs */
> +       };
>  };
>
>  #define TCP_SKB_CB(__skb)      ((struct tcp_skb_cb *)&((__skb)->cb[0]))
> --
> 1.8.1
>
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