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:

quoted

On Sat, Oct 19, 2019 at 1:30 AM John Fastabend [off-list ref] wrote:

quoted

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