netdev - Re: [net-next PATCH v2 6/8] udp: Add support for software checksum and GSO

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Date:   Mon, 7 May 2018 06:50:01 +0900
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [net-next PATCH v2 6/8] udp: Add support for software checksum
 and GSO_PARTIAL with GSO offload

On Sat, May 5, 2018 at 3:31 AM, Alexander Duyck
<alexander.duyck@...il.com> wrote:
> From: Alexander Duyck <alexander.h.duyck@...el.com>
>
> This patch adds support for a software provided checksum and GSO_PARTIAL
> segmentation support. With this we can offload UDP segmentation on devices
> that only have partial support for tunnels.
>
> Since we are no longer needing the hardware checksum we can drop the checks
> in the segmentation code that were verifying if it was present.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> ---
>  net/ipv4/udp_offload.c |   28 ++++++++++++++++++----------
>  net/ipv6/udp_offload.c |   11 +----------
>  2 files changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 946d06d2aa0c..fd94bbb369b2 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -217,6 +217,13 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
>                 return segs;
>         }
>
> +       /* GSO partial and frag_list segmentation only requires splitting
> +        * the frame into an MSS multiple and possibly a remainder, both
> +        * cases return a GSO skb. So update the mss now.
> +        */
> +       if (skb_is_gso(segs))
> +               mss *= skb_shinfo(segs)->gso_segs;
> +
>         seg = segs;
>         uh = udp_hdr(seg);
>
> @@ -237,6 +244,11 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
>                 uh->len = newlen;
>                 uh->check = check;
>
> +               if (seg->ip_summed == CHECKSUM_PARTIAL)
> +                       gso_reset_checksum(seg, ~check);
> +               else
> +                       uh->check = gso_make_checksum(seg, ~check);

Here and below, this needs

  if (uh->check == 0)
    uh->check = CSUM_MANGLED_0;

similar to __skb_udp_tunnel_segment?