Subject: Re: [PATCH v9 bpf-next 10/14] bpf: Add d_path helper

From: Jiri Olsa <[email-masked]>
Date: Wed, 5 Aug 2020 23:01:01 +0200

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 <[email-masked]> 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 <[email-masked]>
> > > ---
> > >  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

jirka