netdev - Re: [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup

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Message-ID: <20190604184306.362d9d8e@carbon>
Date:   Tue, 4 Jun 2019 18:43:06 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     brouer@...hat.com, <netdev@...r.kernel.org>, <kernel-team@...com>,
        <bjorn.topel@...el.com>, <magnus.karlsson@...el.com>,
        <ast@...nel.org>, <daniel@...earbox.net>
Subject: Re: [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an
 xskmap

On Mon, 3 Jun 2019 09:38:51 -0700
Jonathan Lemon <jonathan.lemon@...il.com> wrote:

> Currently, the AF_XDP code uses a separate map in order to
> determine if an xsk is bound to a queue.  Instead of doing this,
> have bpf_map_lookup_elem() return the queue_id, as a way of
> indicating that there is a valid entry at the map index.

Just a reminder, that once we choose a return value, there the
queue_id, then it basically becomes UAPI, and we cannot change it.

Can we somehow use BTF to allow us to extend this later?



I was also going to point out that, you cannot return a direct pointer
to queue_id, as BPF-prog side can modify this... but Daniel already
pointed this out.
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer