Re: [PATCH] libbpf: Support raw btf placed in the default path

[Tao Chen]

Hi Nakryiko, thank you for your reply. Yes, i happed to put the raw
BTF made by myself in /boot on kernel4.19, unluckly it reported error.
So is it possible to allow the raw BTF in /boot directly, athough we
can set the specified btf location again to solve the problem with the
bpf_object_open_opts interface. 


As you say, maybe we can remove the locations[i].raw_btf check, just
use the btf__parse. It looks more concise.


在 2022/8/26 上午4:26, Andrii Nakryiko 写道:
> On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
> <chentao.kernel@xxxxxxxxxxxxxxxxx> wrote:
> > Now only elf btf can be placed in the default path, raw btf should
> > also can be there.
>
> It's not clear what you are trying to achieve. Do you want libbpf to
> attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
> of sneak in pregenerated BTF), or what exactly?
> btf__load_vmlinux_btf() code already supports loading raw BTF, it just
> needs to be explicitly specified in locations table.
>
> So with your change locations[i].raw_btf check doesn't make sense and
> we need to clean this up.
>
> But first, let's discuss the use case, instead of your specific solution.
>
>
> > Signed-off-by: chentao.ct <chentao.kernel@xxxxxxxxxxxxxxxxx>
> > ---
> >   tools/lib/bpf/btf.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> > index bb1e06e..b22b5b3 100644
> > --- a/tools/lib/bpf/btf.c
> > +++ b/tools/lib/bpf/btf.c
> > @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
> >          } locations[] = {
> >                  /* try canonical vmlinux BTF through sysfs first */
> >                  { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
> > -               /* fall back to trying to find vmlinux ELF on disk otherwise */
> > +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
> >                  { "/boot/vmlinux-%1$s" },
> >                  { "/lib/modules/%1$s/vmlinux-%1$s" },
> >                  { "/lib/modules/%1$s/build/vmlinux" },
> > @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
> >                  if (locations[i].raw_btf)
> >                          btf = btf__parse_raw(path);
> >                  else
> > -                       btf = btf__parse_elf(path, NULL);
> > +                       btf = btf__parse(path, NULL);
> >                  err = libbpf_get_error(btf);
> >                  pr_debug("loading kernel BTF '%s': %d\n", path, err);
> >                  if (err)
> > --
> > 2.2.1