Re: [PATCH bpf-next 09/10] libbpf: simplify look up by name of internal maps

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On Tue, Oct 12, 2021 at 8:29 AM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> On Mon, Oct 11, 2021 at 8:45 PM Andrii Nakryiko
> <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > On Mon, Oct 11, 2021 at 11:24 PM Alexei Starovoitov <ast@xxxxxx> wrote:
> > >
> > > On 10/8/21 2:44 PM, Toke Høiland-Jørgensen wrote:
> > > >
> > > > Hmm, so introduce a new 'map_name_long' field, and on query the kernel
> > > > will fill in the old map_name with a truncated version, and put the full
> > > > name in the new field? Yeah, I guess that would work too!
> > >
> > > Let's start storing full map names in BTF instead.
> > > Like we do already for progs.
> > > Some tools already fetch full prog names this way.
> >
> > We do have those names in BTF. Each map has either corresponding VAR
> > or DATASEC. The problem is that we don't know which.
> >
> > Are you proposing to add some extra "btf_def_type_id" field to specify
> > BTF type ID of what "defines" the map (VAR or DATASEC)? That would
> > work. Would still require UAPI and kernel changes, of course.
> >
> > The reason Toke and others were asking to preserve that object name
> > prefix for .rodata/.data maps was different though, and won't be
> > addressed by the above. Even if you know the BTF VAR/DATASEC, you
> > don't know the "object name" associated with the map. And the kernel
> > doesn't know because it's purely libbpf's abstraction. And sometimes
> > that abstraction doesn't make sense (e.g., if we create a map that's
> > pinned and reused from multiple BPF apps/objects).
>
> [..]
>
> > We do have BPF metadata that Stanislav added a while ago, so maybe we
> > should just punt that problem to that? I'd love to have clean
> > ".rodata" and ".data" names, of course.
>
> Are you suggesting we add some option to associate the metadata with
> the maps (might be an option)? IIRC, the metadata can only be
> associated with the progs right now.

Well, maps have associated BTF fd, when they are created, no? So you
can find all the same metadata for the map, no?




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