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

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Date:   Wed, 5 Aug 2020 14:09:49 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <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 Wed, Aug 5, 2020 at 2:01 PM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Wed, Aug 05, 2020 at 07:58:54PM +0200, Jiri Olsa wrote:
> > On Tue, Aug 04, 2020 at 11:35:53PM -0700, Andrii Nakryiko wrote:
> > > On Sat, Aug 1, 2020 at 10:04 AM Jiri Olsa <jolsa@...nel.org> 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)
> > >
> > > nit: probably would be good to do `const struct path *` here, even if
> > > we don't do const-ification properly in all helpers.
>
> hum, for this I need to update scripts/bpf_helpers_doc.py and it looks
> like it's not ready for const struct yet:
>
>   CLNG-LLC [test_maps] get_cgroup_id_kern.o
> In file included from progs/test_lwt_ip_encap.c:7:
> In file included from /home/jolsa/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:11:
> /home/jolsa/linux/tools/testing/selftests/bpf/tools/include/bpf/bpf_helper_defs.h:32:1: warning: 'const' ignored on this declaration [-Wmissing-declarations]
> const struct path;
> ^
>
> would it be ok as a follow up change? I'll need to check
> on bpf_helpers_doc.py script first

yeah, no big deal

>
> jirka
>