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

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Date:   Sun, 6 May 2018 15:13:24 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...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 Sun, May 6, 2018 at 2:50 PM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
> 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?

Good call, though I think I might change this up a bit and do something like:
uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;

That way I can avoid the extra read.

Thanks.

- Alex