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

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Message-Id: <1445970551.497935.421785961.521DBDF0@webmail.messagingengine.com>
Date:	Tue, 27 Oct 2015 19:29:11 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Tom Herbert <tom@...bertland.com>
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 18:32, Tom Herbert wrote:
> 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 lack of correct driver support is a big bumper, but as I wrote, I
don't see a reason to not lift this restriction in net-next. I proposed
a new feature flag, or by looking at your series, we could probably use
the extension header okay field for that.

I would be conservative in net though.

Bye,
Hannes
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