netdev - Re: [PATCH bpf v3] libbpf: handle symbol versioning properly for libbpf.a

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Message-ID: <a508b199-d6b9-26ee-a3f6-2012c9fdde37@fb.com>
Date:   Mon, 30 Sep 2019 16:56:05 +0000
From:   Yonghong Song <yhs@...com>
To:     Alexei Starovoitov <ast@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        Kevin Laatz <kevin.laatz@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf v3] libbpf: handle symbol versioning properly for
 libbpf.a



On 9/30/19 9:42 AM, Alexei Starovoitov wrote:
> On 9/30/19 9:29 AM, Yonghong Song wrote:
>> +OLD_VERSION(xsk_umem__create_v0_0_2, xsk_umem__create, LIBBPF_0.0.2)
>> +NEW_VERSION(xsk_umem__create_v0_0_4, xsk_umem__create, LIBBPF_0.0.4)
> 
> how this will look when yet another version of this function is
> introduced, say in 0.0.6 ?
> 
> OLD_VERSION(xsk_umem__create_v0_0_2, xsk_umem__create, LIBBPF_0.0.2)
> OLD_VERSION(xsk_umem__create_v0_0_4, xsk_umem__create, LIBBPF_0.0.4)
> NEW_VERSION(xsk_umem__create_v0_0_6, xsk_umem__create, LIBBPF_0.0.6)

Yes.

> 
> 0.0.4 will be renamed to OLD_ and the latest addition NEW_ ?

Right.

> The macro name feels a bit confusing. May be instead of NEW_
> call it CURRENT_ ? or DEFAULT_ ?
> NEW_ will become not so 'new' few months from now.

Right. After a few months, the version number may indeed be
behind the libbpf versions.... "current" may not be current ....
Let me use DEFAULT then. How about using
    COMPAT_VERSION(...)
for old versions, and using
    DEFAULT_VERSION(...)
for the new version?