netdev - Re: [PATCH v3 bpf-next 2/2] selftests/bpf: add tests for BPF_F_PRESERVE

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Date:   Wed, 30 Sep 2020 12:26:47 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com,
        ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
        kpsingh@...omium.org
Subject: Re: [PATCH v3 bpf-next 2/2] selftests/bpf: add tests for
 BPF_F_PRESERVE_ELEMS

On Wed, Sep 30, 2020 at 08:20:58AM -0700, Song Liu wrote:
> diff --git a/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
> new file mode 100644
> index 0000000000000..dc77e406de41f
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_pe_preserve_elems.c
> @@ -0,0 +1,44 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2020 Facebook
> +#include "vmlinux.h"

Does it actually need vmlinux.h ?
Just checking to make sure it compiles on older kernels.

> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(int));
> +} array_1 SEC(".maps");
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +	__uint(max_entries, 1);
> +	__uint(key_size, sizeof(int));
> +	__uint(value_size, sizeof(int));
> +	__uint(map_flags, BPF_F_PRESERVE_ELEMS);
> +} array_2 SEC(".maps");
> +
> +SEC("raw_tp/sched_switch")
> +int BPF_PROG(read_array_1)
> +{
> +	struct bpf_perf_event_value val;
> +	long ret;
> +
> +	ret = bpf_perf_event_read_value(&array_1, 0, &val, sizeof(val));
> +	bpf_printk("read_array_1 returns %ld", ret);
> +	return ret;
> +}
> +
> +SEC("raw_tp/task_rename")
> +int BPF_PROG(read_array_2)
> +{
> +	struct bpf_perf_event_value val;
> +	long ret;
> +
> +	ret = bpf_perf_event_read_value(&array_2, 0, &val, sizeof(val));
> +	bpf_printk("read_array_2 returns %ld", ret);

Please remove printk from the tests. It only spams the trace_pipe.

> +	return ret;

The return code is already checked as far as I can see.
That's enough to pass/fail the test, right?