netdev - Re: [RFC net-next PATCH 4/5] net: new XDP feature for reading HW rxhash from drivers

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Message-ID: <20170519202147.3c6bda7f@cakuba.netronome.com>
Date:   Fri, 19 May 2017 20:21:47 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        John Fastabend <john.r.fastabend@...el.com>,
        netdev@...r.kernel.org
Subject: Re: [RFC net-next PATCH 4/5] net: new XDP feature for reading HW
 rxhash from drivers

On Fri, 19 May 2017 20:07:52 -0700, Alexei Starovoitov wrote:
> How about exposing 'struct mlx5_cqe64 *' to XDP programs as-is?
> We can make sure that XDP program does read only access into it and
> it will see cqe->rss_hash_result, cqe->rss_hash_type and everything else
> in there, but this will not be uapi and it will be pretty obvious
> to program authors that their programs are vendor specific.
> 'not uapi' here means that mellanox is free to change their HW descriptor
> and its contents as they wish.

Hm..  Would that mean we have to teach the verifier about all possible
drivers and their metadata structures (i.e. sizes thereof).  And add an
UAPI enum of known drivers?

Other idea I floated in early days was to standardize the fields but
let the driver "JIT" the accesses to look at the right offset of the
right structure.  Admittedly that would be a lot more work.