netdev - Re: [PATCH bpf-next RFC 2/3] bpf: devmap dynamic map-value storage area based on BTF

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Message-ID: <CAEf4BzbL1ftGZ9x0hvFDc-PGNexTuMv67VxT=q2NF0y6im6+cg@mail.gmail.com>
Date:   Sat, 30 May 2020 00:19:50 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     David Ahern <dsahern@...il.com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH bpf-next RFC 2/3] bpf: devmap dynamic map-value storage
 area based on BTF

On Fri, May 29, 2020 at 8:59 AM Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> The devmap map-value can be read from BPF-prog side, and could be used for a
> storage area per device. This could e.g. contain info on headers that need

If BPF program needs a storage area per device, why can't it just use
a separate map or just plain array (both keyed by ifindex) to store
whatever it needs per-device? It's not clear why this flexibility and
complexity is needed from the description above.

> to be added when packet egress this device.
>
> This patchset adds a dynamic storage member to struct bpf_devmap_val. More
> importantly the struct bpf_devmap_val is made dynamic via leveraging and
> requiring BTF for struct sizes above 4. The only mandatory struct member is
> 'ifindex' with a fixed offset of zero.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>  kernel/bpf/devmap.c |  216 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 185 insertions(+), 31 deletions(-)
>

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