netdev - Re: [PATCH bpf-next 4/9] libbpf: add libbpf_swap

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Message-ID: <20190727003045.63s6qau6kcnpkgxq@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 26 Jul 2019 17:30:46 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Stanislav Fomichev <sdf@...ichev.me>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 4/9] libbpf: add libbpf_swap_print to get
 previous print func

On Fri, Jul 26, 2019 at 02:47:28PM -0700, Andrii Nakryiko wrote:
> On Fri, Jul 26, 2019 at 2:28 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
> >
> > On 07/26, Andrii Nakryiko wrote:
> > > libbpf_swap_print allows to restore previously set print function.
> > > This is useful when running many independent test with one default print
> > > function, but overriding log verbosity for particular subset of tests.
> > Can we change the return type of libbpf_set_print instead and return
> > the old function from it? Will it break ABI?
> 
> Yeah, thought about that, but I wasn't sure about ABI breakage. It
> seems like it shouldn't, so I'll just change libbpf_set_print
> signature instead.

I think it's ok to change return value of libbpf_set_print() from void
to useful pointer.
This function is not marked as __attribute__((__warn_unused_result__)),
so there should be no abi issues.

Please double check by compiler perf with different gcc-s as Arnaldo's setup does.