linux-kernel - Re: [PATCH bpf-next 1/4] selftests/bpf: convert get_current_cgroup_id_user to test

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Message-ID: <f60d47cc-84ff-4031-a9e6-244954af901e@bootlin.com>
Date: Wed, 31 Jul 2024 20:53:21 +0200
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Alan Maguire <alan.maguire@...cle.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>
Cc: ebpf@...uxfoundation.org, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/4] selftests/bpf: convert
 get_current_cgroup_id_user to test_progs

Hello Alan,

On 7/31/24 19:23, Alan Maguire wrote:
> On 31/07/2024 11:38, Alexis Lothoré (eBPF Foundation) wrote:

[...]

>> +	pid = getpid();
>> +	if (!ASSERT_OK(bpf_map__update_elem(skel->maps.pidmap, &key,
>> +					    sizeof(key), &pid, sizeof(pid), 0),
>> +		       "write pid"))
>> +		goto cleanup_progs;
>> +
> 
> I think it would be worth using a global variable in the BPF program
> my_pid, and setting skel->bss->my_pid here as other more up-to-date
> tests do (example progs/test_usdt.c, prog_tests/usdt.c). No need for a
> separate map anymore.

That sounds like a good improvement, thanks for the hint and the example :) I'll
spin a new revision with this, and make sure to use it in my next test
conversion patches too when relevant.

TBH I am not familiar with global variables usage in ebpf/libbpf, so it is not
clear for me when I should prefer it over classic maps. From some quick search I
feel like it should be the default choice when needing basic controls
knobs/feedback on a bpf program from userspace ? Or maybe it should be used even
more broadly by default ?

>> +	/* trigger the syscall on which is attached the tested prog */
>> +	if (!ASSERT_OK(syscall(__NR_nanosleep, &req, NULL), "nanosleep"))
>> +		goto cleanup_progs;
>> +
>> +	if (!ASSERT_OK(bpf_map__lookup_elem(skel->maps.cg_ids, &key,
>> +					    sizeof(key), &kcgid, sizeof(kcgid),
>> +					    0),
>> +		       "read bpf cgroup id"))
>> +		goto cleanup_progs;
>> +
> 
> ditto here, cg_ids could be a global var cg_id that the bpf prog sets
> and we check here via skel->bss->cg_id.

ACK, I'll update this too.

Thanks,

Alexis

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com