netdev - Re: [PATCH net v2 3/4] ipv6: no CHECKSUM_PARTIAL on MSG

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Date:	Tue, 27 Oct 2015 10:32:42 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Vladislav Yasevich <vyasevich@...il.com>,
	Benjamin Coddington <bcodding@...hat.com>
Subject: Re: [PATCH net v2 3/4] ipv6: no CHECKSUM_PARTIAL on MSG_MORE corked sockets

On Tue, Oct 27, 2015 at 9:44 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
>
>
> On Tue, Oct 27, 2015, at 17:36, Tom Herbert wrote:> > -               if
> (cork->length + length > maxnonfragsize - headersize) {
>> > +       if (cork->length + length > maxnonfragsize - headersize) {
>> >  emsgsize:
>> > -                       ipv6_local_error(sk, EMSGSIZE, fl6,
>> > -                                        mtu - headersize +
>> > -                                        sizeof(struct ipv6hdr));
>> > -                       return -EMSGSIZE;
>> > -               }
>> > +               ipv6_local_error(sk, EMSGSIZE, fl6,
>> > +                                mtu - headersize +
>> > +                                sizeof(struct ipv6hdr));
>> > +               return -EMSGSIZE;
>> >         }
>> >
>> > +       /* CHECKSUM_PARTIAL only with no extension headers and when
>>
>> No, please don't do this. CHECKSUM_PARTIAL should work with extension
>> headers as defined, so this is just disabling otherwise valid and
>> useful functionality. If (some) drivers have problems with this they
>> need to be identified and fixed.
>
> I don't understand. The old code already didn't allow the use of
> opt_flen with CHECKSUM_PARTIAL.
>
Then that's a problem with the old code :-). Is there any other reason
that we can't use CHECKSUM_PARTIAL with extension headers other than
lack of correct driver support?

> The MSG_MORE check has nothing to do with that but only with corking.
>
> Bye,
> Hannes
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