Subject: Re: [PATCH 09/11] bpf: Add d_path helper

From: Jiri Olsa <[email-masked]>
Date: Fri, 19 Jun 2020 15:31:24 +0200

On Thu, Jun 18, 2020 at 09:35:10PM -0700, Andrii Nakryiko wrote:
> On Tue, Jun 16, 2020 at 3:07 AM Jiri Olsa <[email-masked]> wrote:
> >
> > Adding d_path helper function that returns full path
> > for give 'struct path' object, which needs to be the
> > kernel BTF 'path' object.
> >
> > The helper calls directly d_path function.
> >
> > Updating also bpf.h tools uapi header and adding
> > 'path' to bpf_helpers_doc.py script.
> >
> > Signed-off-by: Jiri Olsa <[email-masked]>
> > ---
> >  include/linux/bpf.h            |  4 ++++
> >  include/uapi/linux/bpf.h       | 14 ++++++++++++-
> >  kernel/bpf/btf_ids.c           | 11 ++++++++++
> >  kernel/trace/bpf_trace.c       | 38 ++++++++++++++++++++++++++++++++++
> >  scripts/bpf_helpers_doc.py     |  2 ++
> >  tools/include/uapi/linux/bpf.h | 14 ++++++++++++-
> >  6 files changed, 81 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index a94e85c2ec50..d35265b6c574 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1752,5 +1752,9 @@ extern int bpf_skb_output_btf_ids[];
> >  extern int bpf_seq_printf_btf_ids[];
> >  extern int bpf_seq_write_btf_ids[];
> >  extern int bpf_xdp_output_btf_ids[];
> > +extern int bpf_d_path_btf_ids[];
> > +
> > +extern int btf_whitelist_d_path[];
> > +extern int btf_whitelist_d_path_cnt;
> 
> So with suggestion from previous patch, this would be declared as:
> 
> extern const struct btf_id_set btf_whitelist_d_path;

yes

SNIP

> >  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> >   * function eBPF program intends to call
> > diff --git a/kernel/bpf/btf_ids.c b/kernel/bpf/btf_ids.c
> > index d8d0df162f04..853c8fd59b06 100644
> > --- a/kernel/bpf/btf_ids.c
> > +++ b/kernel/bpf/btf_ids.c
> > @@ -13,3 +13,14 @@ BTF_ID(struct, seq_file)
> >
> >  BTF_ID_LIST(bpf_xdp_output_btf_ids)
> >  BTF_ID(struct, xdp_buff)
> > +
> > +BTF_ID_LIST(bpf_d_path_btf_ids)
> > +BTF_ID(struct, path)
> > +
> > +BTF_WHITELIST_ENTRY(btf_whitelist_d_path)
> > +BTF_ID(func, vfs_truncate)
> > +BTF_ID(func, vfs_fallocate)
> > +BTF_ID(func, dentry_open)
> > +BTF_ID(func, vfs_getattr)
> > +BTF_ID(func, filp_close)
> > +BTF_WHITELIST_END(btf_whitelist_d_path)
> 
> Oh, so that's why you added btf_ids.c. Do you think centralizing all
> those BTF ID lists in one file is going to be more convenient? I lean
> towards keeping them closer to where they are used, as it was with all
> those helper BTF IDS. But I wonder what others think...

either way works for me, but then BTF_ID_* macros needs to go
to include/linux/btf_ids.h header right?

jirka

> 
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index c1866d76041f..0ff5d8434d40 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1016,6 +1016,42 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = {
> >         .arg1_type      = ARG_ANYTHING,
> >  };
> >
> 
> [...]
>