netdev - Re: [PATCH v9 bpf-next 10/14] bpf: Add d

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Message-ID: <20200802031342.3bfxqo22ezi2zzu4@ast-mbp.dhcp.thefacebook.com>
Date:   Sat, 1 Aug 2020 20:13:42 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Song Liu <songliubraving@...com>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        David Miller <davem@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Wenbo Zhang <ethercflow@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Brendan Gregg <bgregg@...flix.com>,
        Florent Revest <revest@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v9 bpf-next 10/14] bpf: Add d_path helper

On Sat, Aug 01, 2020 at 07:03:18PM +0200, Jiri Olsa wrote:
> Adding d_path helper function that returns full path for
> given 'struct path' object, which needs to be the kernel
> BTF 'path' object. The path is returned in buffer provided
> 'buf' of size 'sz' and is zero terminated.
> 
>   bpf_d_path(&file->f_path, buf, size);
> 
> The helper calls directly d_path function, so there's only
> limited set of function it can be called from. Adding just
> very modest set for the start.
> 
> Updating also bpf.h tools uapi header and adding 'path' to
> bpf_helpers_doc.py script.
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/uapi/linux/bpf.h       | 13 +++++++++
>  kernel/trace/bpf_trace.c       | 48 ++++++++++++++++++++++++++++++++++
>  scripts/bpf_helpers_doc.py     |  2 ++
>  tools/include/uapi/linux/bpf.h | 13 +++++++++
>  4 files changed, 76 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index eb5e0c38eb2c..a356ea1357bf 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3389,6 +3389,18 @@ union bpf_attr {
>   *		A non-negative value equal to or less than *size* on success,
>   *		or a negative error in case of failure.
>   *
> + * int bpf_d_path(struct path *path, char *buf, u32 sz)

Please make it return 'long'. As you well ware the generated code will be better.