Re: BPF program metadata

[sdf@google.com]

On 08/05, Alexei Starovoitov wrote:
> On Tue, Aug 4, 2020 at 12:42 PM <sdf@google.com> wrote:
> >
> > On 07/29, sdf@google.com wrote:
> > > As discussed in
> > >  
> https://docs.google.com/presentation/d/1A9Anx8JPHl_pK1aXy8hlxs3V5pkrKwHHtkPf_-HeYTc
> > > during BPF office hours, we'd like to attach arbitrary auxiliary
> > > metadata to the program, for example, the build timestamp or the  
> commit
> > > hash.
> >
> > > IIRC, the suggestion was to explore BTF and .BTF.ext section in
> > > particular.
> > > We've spent some time looking at the BTF encoding and BTF.ext section
> > > and we don't see how we can put this data into .BTF.ext or even .BTF
> > > without any kernel changes.
> >
> > > The reasoning (at least how we see it):
> > > * .BTF.ext is just a container with  
> func_info/line_info/relocation_info
> > >    and libbpf extracts the data form this section and passes it to
> > >    sys_bpf(BPF_PROG_LOAD); the important note is that it doesn't pass  
> the
> > >    whole container to the kernel, but passes the data that's been
> > >    extracted from the appropriate sections
> > > * .BTF can be used for metadata, but it looks like we'd have to add
> > >    another BTF_INFO_KIND() to make it a less messy (YiFei, feel free  
> to
> > >    correct me)
> >
> > > So the question is: are we missing something? Is there some way to add
> > > key=value metadata to BTF that doesn't involve a lot of kernel  
> changes?
> >
> > > If the restrictions above are correct, should we go back to trying to
> > > put this metadata into .data section (or maybe even the new .metadata
> > > section)? The only missing piece of the puzzle in that case is the
> > > ability to extend BPF_PROG_LOAD with a way to say 'hold this map
> > > unconditionally'.
> > Should we have a short discussion about that this Thu during the office
> > hours?

> Of course. That's what office hours are for.
> Since google folks have trouble with zoom I've added google meets link
> to the spreadsheet. Let's try it tomorrow.
Ooooh, thank you for the Google Meets link :-)