netdev - Re: [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on BTF

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Date:   Thu, 4 Jun 2020 10:40:06 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH bpf-next V1] bpf: devmap dynamic map-value area based on
 BTF

On 6/4/20 9:48 AM, Jesper Dangaard Brouer wrote:
> I will NOT send a patch that expose this in uapi/bpf.h.  As I explained
> before, this caused the issues for my userspace application, that
> automatically picked-up struct bpf_devmap_val, and started to fail
> (with no code changes), because it needed minus-1 as input.  I fear
> that this will cause more work for me later, when I have to helpout and
> support end-users on e.g. xdp-newbies list, as it will not be obvious
> to end-users why their programs map-insert start to fail.  I have given
> up, so I will not NACK anyone sending such a patch.
> 
> Why is it we need to support file-descriptor zero as a valid
> file-descriptor for a bpf-prog?

That was a nice property of using the id instead of fd. And the init to
-1 is not unique to this; adopters of the bpf_set_link_xdp_fd_opts for
example have to do the same.