netdev - Re: [bpf-next PATCH] bpf: libbpf, support older style kprobe load

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Message-ID: <20191022072023.GA31343@pc-66.home>
Date:   Tue, 22 Oct 2019 09:20:23 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [bpf-next PATCH] bpf: libbpf, support older style kprobe load

On Mon, Oct 21, 2019 at 10:07:59PM -0700, John Fastabend wrote:
> Andrii Nakryiko wrote:
> > On Sat, Oct 19, 2019 at 1:30 AM John Fastabend <john.fastabend@...il.com> wrote:
> > >
> > > Following ./Documentation/trace/kprobetrace.rst add support for loading
> > > kprobes programs on older kernels.
> > 
> > My main concern with this is that this code is born bit-rotten,
> > because selftests are never testing the legacy code path. How did you
> > think about testing this and ensuring that this keeps working going
> > forward?
> 
> Well we use it, but I see your point and actually I even broke the retprobe
> piece hastily fixing merge conflicts in this patch. When I ran tests on it
> I missed running retprobe tests on the set of kernels that would hit that
> code.

If it also gets explicitly exposed as bpf_program__attach_legacy_kprobe() or
such, it should be easy to add BPF selftests for that API to address the test
coverage concern. Generally more selftests for exposed libbpf APIs is good to
have anyway.

Cheers,
Daniel