netdev - Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff and xdp

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Date:   Sat, 29 May 2021 15:37:28 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Tom Herbert <tom@...bertland.com>, bpf@...r.kernel.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eelco Chaudron <echaudro@...hat.com>,
        David Ahern <dsahern@...il.com>, magnus.karlsson@...el.com,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>, bjorn@...nel.org,
        Maciej Fijałkowski (Intel) 
        <maciej.fijalkowski@...el.com>,
        john fastabend <john.fastabend@...il.com>
Subject: Re: [RFC bpf-next 1/4] net: xdp: introduce flags field in xdp_buff
 and xdp_frame

> On Fri, 28 May 2021 14:18:33 -0700 Tom Herbert wrote:
> > On Fri, May 28, 2021 at 10:44 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> > > Introduce flag field in xdp_buff and xdp_frame data structure in order
> > > to report xdp_buffer metadata. For the moment just hw checksum hints
> > > are defined but flags field will be reused for xdp multi-buffer
> > > For the moment just CHECKSUM_UNNECESSARY is supported.
> > > CHECKSUM_COMPLETE will need to set csum value in metada space.
> > >  
> > Lorenzo,
> > 
> > This isn't sufficient for the checksum-unnecessary interface, we'd
> > also need ability to set csum_level for cases the device validated
> > more than one checksum.
> > 
> > IMO, we shouldn't support CHECKSUM_UNNECESSARY for new uses like this.
> > For years now, the Linux community has been pleading with vendors to
> > provide CHECKSUM_COMPLETE which is far more useful and robust than
> > CHECSUM_UNNECESSARY, and yet some still haven't got with the program
> > even though we see more and more instances where CHECKSUM_UNNECESSARY
> > doesn't even work at all (e.g. cases with SRv6, new encaps device
> > doesn't understand). I believe it's time to take a stand! :-)
> 
> I must agree. Not supporting CHECKSUM_COMPLETE seems like a step back.

I completely agree on it and I want add support for CHECKSUM_COMPLETE as soon
as we decide what is the best way to store csum value (xdp_metadata?). At the
same time this preliminary series wants to add support just for
CHECSUM_UNNECESSARY. Moreover the flags field in xdp_buff/xdp_frame will be
reused for xdp multi-buff work.

Regards,
Lorenzo

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