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Date:   Fri, 22 May 2020 12:11:02 -0600
From:   David Ahern <>
To:     Jesper Dangaard Brouer <>,
        David Ahern <>
Cc:,,,,,,,,,,, Lorenzo Bianconi <>
Subject: Re: [PATCH RFC bpf-next 1/4] bpf: Handle 8-byte values in DEVMAP and

On 5/22/20 10:04 AM, Jesper Dangaard Brouer wrote:
> On Fri, 22 May 2020 14:08:05 +0200
> Jesper Dangaard Brouer <> wrote:
>> On Thu, 21 May 2020 19:05:23 -0600
>> David Ahern <> wrote:
>>> Add support to DEVMAP and DEVMAP_HASH to support 8-byte values as a
>>> <device index, program id> pair. To do this, a new struct is needed in
>>> bpf_dtab_netdev to hold the values to return on lookup.  
>> I would like to see us leverage BTF instead of checking on the size
>> attr->value_size. E.g do the sanity check based on BTF.
>> Given I don't know the exact details on how this should be done, I will
>> look into it... I already promised Lorenzo, as we have already
>> discussed this on IRC.
>> So, you can Lorenzo can go ahead with this approach, and test the
>> use-case. And I'll try to figure out if-and-how we can leverage BTF
>> here.  Input from BTF experts will be much appreciated.
> Published my current notes here:
> And created PR that people can GitHub "subscribe" to, if you are interested:

thanks for compiling some notes.

Fundamentally, I do not see how this can work for something like the
program id where the kernel needs to know not just the type (u32) but
that it should take the id and do a lookup - convert the id into a
bpf_prog reference.

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