linux-kernel - Re: [PATCH/RFC] Re: 'perf test BPF' failing, libbpf regression wrt "basic API for BPF obj name"

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Message-ID: <31839372-05b5-3704-4e04-96ff810c1327@fb.com>
Date:   Fri, 1 Dec 2017 17:15:07 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     Martin KaFai Lau <kafai@...com>, Wang Nan <wangnan0@...wei.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH/RFC] Re: 'perf test BPF' failing, libbpf regression wrt
 "basic API for BPF obj name"

On 12/1/17 9:51 AM, Arnaldo Carvalho de Melo wrote:
>
> But this is not just testcase expectations, the usecase is someone
> wanting to use a newer tool, with perhaps some new features of interest
> that don't depend on changes in the kernel, in an older kernel on a
> system where updating it is not possible or desirable.

I think it's also dangerous for the core library like libbpf to
be smarter than the tool that is using it.
In this case we added prog and map names by default into loader and
create_map functions to make sure that all tools pick them up
automatically and we can see a bit more human readable bpf names
in kernel stack traces and in debug tools like bpftool, bcc/bps.
When kernel is older and doesn't support prog/map names, it's perfectly
reasonable to fall back to map creation without the name, but
library shouldn't be doing it in all cases.
Like prog_load command recently got new prog_ifindex field.
It would be incorrect to fallback to loading without it.