netdev - Re: [PATCH net-next 1/2] bpf_xdp_redirect_map: Add flag to return XDP

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Date:   Wed, 05 Jun 2019 08:09:50 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Jesper Dangaard Brouer" <brouer@...hat.com>
Cc:     "Toke Høiland-Jørgensen" <toke@...hat.com>,
        "David Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "Alexei Starovoitov" <ast@...nel.org>
Subject: Re: [PATCH net-next 1/2] bpf_xdp_redirect_map: Add flag to return
 XDP_PASS on map lookup failure



On 5 Jun 2019, at 3:39, Jesper Dangaard Brouer wrote:

> On Tue, 04 Jun 2019 17:24:10 +0200
> Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
>> The bpf_redirect_map() helper used by XDP programs doesn't return any
>> indication of whether it can successfully redirect to the map index 
>> it was
>> given. Instead, BPF programs have to track this themselves, leading 
>> to
>> programs using duplicate maps to track which entries are populated in 
>> the
>> devmap.
>>
>> This adds a flag to the XDP version of the bpf_redirect_map() helper, 
>> which
>> makes the helper do a lookup in the map when called, and return 
>> XDP_PASS if
>> there is no value at the provided index. This enables two use cases:
>
> To Jonathan Lemon, notice this approach of adding a flag to the helper
> call, it actually also works for your use-case of XSK AF_XDP maps.c

Hmm, yes, that should work also.

I have a patch which returns a XDP_SOCK type from the xskmap.
This could be used with a new helper for redirection directly to a 
socket
(instead of looking the socket up a second time).

While flexible, the downside is that this won't apply to devmaps.
-- 
Jonathan