Re: [PATCH v4 bpf-next 13/14] selftests/bpf: Add test for d_path helper

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Wenbo Zhang <ethercflow@gmail.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>, Andrii Nakryiko <andriin@fb.com>,
	Brendan Gregg <bgregg@netflix.com>,
	Florent Revest <revest@chromium.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v4 bpf-next 13/14] selftests/bpf: Add test for d_path helper
Date: Fri, 26 Jun 2020 14:55:34 -0700	[thread overview]
Message-ID: <CAEf4BzYpYXN6nZc1CT3ZHUoeYfALK_SY2cLUZ7G72ka5GL_33Q@mail.gmail.com> (raw)
In-Reply-To: <20200625221304.2817194-14-jolsa@kernel.org>

On Thu, Jun 25, 2020 at 4:49 PM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding test for d_path helper which is pretty much
> copied from Wenbo Zhang's test for bpf_get_fd_path,
> which never made it in.
>
> I've failed so far to compile the test with <linux/fs.h>
> kernel header, so for now adding 'struct file' with f_path
> member that has same offset as kernel's file object.
>
> Original-patch-by: Wenbo Zhang <ethercflow@gmail.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  .../testing/selftests/bpf/prog_tests/d_path.c | 145 ++++++++++++++++++
>  .../testing/selftests/bpf/progs/test_d_path.c |  50 ++++++
>  2 files changed, 195 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/d_path.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_d_path.c
>

[...]

> diff --git a/tools/testing/selftests/bpf/progs/test_d_path.c b/tools/testing/selftests/bpf/progs/test_d_path.c
> new file mode 100644
> index 000000000000..6096aef2bafc
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_d_path.c
> @@ -0,0 +1,50 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#define MAX_PATH_LEN           128
> +#define MAX_EVENT_NUM          16
> +
> +pid_t my_pid;
> +__u32 cnt_stat;
> +__u32 cnt_close;
> +char paths_stat[MAX_EVENT_NUM][MAX_PATH_LEN];
> +char paths_close[MAX_EVENT_NUM][MAX_PATH_LEN];
> +
> +SEC("fentry/vfs_getattr")
> +int BPF_PROG(prog_stat, struct path *path, struct kstat *stat,
> +            __u32 request_mask, unsigned int query_flags)
> +{
> +       pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +       if (pid != my_pid)
> +               return 0;
> +
> +       if (cnt_stat >= MAX_EVENT_NUM)
> +               return 0;
> +
> +       bpf_d_path(path, paths_stat[cnt_stat], MAX_PATH_LEN);
> +       cnt_stat++;
> +       return 0;
> +}
> +
> +SEC("fentry/filp_close")
> +int BPF_PROG(prog_close, struct file *file, void *id)
> +{
> +       pid_t pid = bpf_get_current_pid_tgid() >> 32;
> +
> +       if (pid != my_pid)
> +               return 0;
> +
> +       if (cnt_close >= MAX_EVENT_NUM)
> +               return 0;
> +
> +       bpf_d_path((struct path *) &file->f_path,
> +                  paths_close[cnt_close], MAX_PATH_LEN);

Can you please capture the return result of bpf_d_path() (here and
above) and validate that it's correct? That will help avoid future
breakages if anyone changes this.

> +       cnt_close++;
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.25.4
>