netdev - Re: [PATCH bpf-next 2/5] bpf: Add support to attach bpf program to a devmap entry

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Date:   Wed, 27 May 2020 16:58:46 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     David Ahern <dsahern@...il.com>, David Ahern <dsahern@...nel.org>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, brouer@...hat.com,
        daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com
Subject: Re: [PATCH bpf-next 2/5] bpf: Add support to attach bpf program to a devmap entry

David Ahern <dsahern@...il.com> writes:

> On 5/27/20 4:01 AM, Toke Høiland-Jørgensen wrote:
>> Did you give any special consideration to where the hook should be? I'm
>> asking because my immediate thought was that it should be on flush
>> (i.e., in bq_xmit_all()), but now that I see this I'm so sure anymore.
>> What were your thoughts around this?
>
> I chose this spot for many reasons:
>
> 1. dev_map_enqueue has the bpf_dtab_netdev structure which holds the program
>
> 2. programs take xdp_buff, and dev_map_enqueue still has the xdp_buff
> with the rx information; no need to convert from buff to frame losing rx
> data, enqueue, back to buff to run program, back to frame to hand off to
> the driver.
>
> 3. no sense enqueuing if the device program drops the frame.

Right, makes sense; thank you for explaining :)

-Toke