netdev - Re: [Intel-wired-lan] [PATCH bpf-next v4 03/11] libbpf: add flags to umem config

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Message-ID: <CAJ+HfNhQFs4jgJORmdPh6zeJXXMd-9j3YgdSUac3PxRQrGzNDw@mail.gmail.com>
Date:   Fri, 2 Aug 2019 09:26:55 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Kevin Laatz <kevin.laatz@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Bruce Richardson <bruce.richardson@...el.com>,
        ciara.loftus@...el.com,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH bpf-next v4 03/11] libbpf: add flags to
 umem config

On Fri, 2 Aug 2019 at 09:19, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>
> On Thu, Aug 1, 2019 at 12:34 AM Björn Töpel <bjorn.topel@...il.com> wrote:
> >
[...]
> >
> > Old application, dynamically linked to new libbpf.so will crash,
> > right? Old application passes old version of xsk_umem_config, and new
> > library accesses (non-existing) flag struct member.
>
> I think we have similar problems for all the _xattr type of commands
> (as well some of btf stuff accepting extra opts structs). How is this
> problem solved in general? Do we version same function multiple times,
> one for each added field? It feels like there should be some better
> way to handle this...
>

If the size of the struct was passed as an argument (and extra care is
taken when adding members to the struct), it could be handled w/o
versioning... but that's not the case here. :-( Versioning is a mess
to deal with, so I'd be happy if it could be avoided...