linux-kernel - [PATCH bpf-next 0/2] bpftool: fix feature output when helper probes fail

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Message-Id: <20220504161356.3497972-1-milan@mdaverde.com>
Date:   Wed,  4 May 2022 12:13:30 -0400
From:   Milan Landaverde <milan@...verde.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     milan@...verde.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Paul Chaignon <paul@...valent.com>,
        Niklas Söderlund <niklas.soderlund@...igine.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next 0/2] bpftool: fix feature output when helper probes fail

Currently in bpftool's feature probe, we incorrectly tell the user that
all of the helper functions are supported for program types where helper
probing fails or is explicitly unsupported[1]:

$ bpftool feature probe
...
eBPF helpers supported for program type tracing:
	- bpf_map_lookup_elem
	- bpf_map_update_elem
	- bpf_map_delete_elem
	...
	- bpf_redirect_neigh
	- bpf_check_mtu
	- bpf_sys_bpf
	- bpf_sys_close

This patch adjusts bpftool to relay to the user when helper support
can't be determined:

$ bpftool feature probe
...
eBPF helpers supported for program type lirc_mode2:
    Program type not supported
eBPF helpers supported for program type tracing:
    Could not determine which helpers are available
eBPF helpers supported for program type struct_opts:
    Could not determine which helpers are available
eBPF helpers supported for program type ext:
    Could not determine which helpers are available

Rather than imply that no helpers are available for the program type, we
let the user know that helper function probing failed entirely.

[1] https://lore.kernel.org/bpf/20211217171202.3352835-2-andrii@kernel.org/

Milan Landaverde (2):
  bpftool: adjust for error codes from libbpf probes
  bpftool: output message if no helpers found in feature probing

 tools/bpf/bpftool/feature.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

--
2.32.0