Re: [PATCH v22 bpf-next 18/23] libbpf: Add SEC name for xdp multi-frags programs

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Jan 18, 2022 at 2:33 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Jan 18, 2022 at 2:31 PM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> >
> > > On Mon, Jan 17, 2022 at 06:28:30PM +0100, Lorenzo Bianconi wrote:
> > > > Introduce support for the following SEC entries for XDP multi-frags
> > > > property:
> > > > - SEC("xdp.frags")
> > > > - SEC("xdp.frags/devmap")
> > > > - SEC("xdp.frags/cpumap")
> > > >
> > > > Acked-by: Toke Hoiland-Jorgensen <toke@redhat.com>
> > > > Acked-by: John Fastabend <john.fastabend@gmail.com>
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > > > ---
> > > >  tools/lib/bpf/libbpf.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > > index fdb3536afa7d..611e81357fb6 100644
> > > > --- a/tools/lib/bpf/libbpf.c
> > > > +++ b/tools/lib/bpf/libbpf.c
> > > > @@ -6562,6 +6562,9 @@ static int libbpf_preload_prog(struct bpf_program *prog,
> > > >     if (def & SEC_SLEEPABLE)
> > > >             opts->prog_flags |= BPF_F_SLEEPABLE;
> > > >
> > > > +   if (prog->type == BPF_PROG_TYPE_XDP && strstr(prog->sec_name, ".frags"))
> > > > +           opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;
> > >
> > > That's a bit sloppy.
> > > Could you handle it similar to SEC_SLEEPABLE?
> > >
> > > > +
> > > >     if ((prog->type == BPF_PROG_TYPE_TRACING ||
> > > >          prog->type == BPF_PROG_TYPE_LSM ||
> > > >          prog->type == BPF_PROG_TYPE_EXT) && !prog->attach_btf_id) {
> > > > @@ -8600,8 +8603,11 @@ static const struct bpf_sec_def section_defs[] = {
> > > >     SEC_DEF("lsm.s/",               LSM, BPF_LSM_MAC, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_lsm),
> > > >     SEC_DEF("iter/",                TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF, attach_iter),
> > > >     SEC_DEF("syscall",              SYSCALL, 0, SEC_SLEEPABLE),
> > > > +   SEC_DEF("xdp.frags/devmap",     XDP, BPF_XDP_DEVMAP, SEC_NONE),
> > > >     SEC_DEF("xdp_devmap/",          XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE),
> > > > +   SEC_DEF("xdp.frags/cpumap",     XDP, BPF_XDP_CPUMAP, SEC_NONE),
> > > >     SEC_DEF("xdp_cpumap/",          XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE),
> > > > +   SEC_DEF("xdp.frags",            XDP, BPF_XDP, SEC_NONE),
> > >
> > > It would be SEC_FRAGS here instead of SEC_NONE.
> >
> > ack, I dropped SEC_FRAGS (SEC_XDP_MB before) from sec_def_flags because Andrii asked to remove
> > it but I am fine to add it back. Agree?
>
> Andrii,
> what was the motivation?
> imo that's cleaner than strstr.

Given it was XDP-specific (as opposed to sleepable flag that applies
more widely), it felt cleaner ([0]) to handle that as a special case
in libbpf_preload_prog. But I didn't feel that strongly about that
back then and still don't, so if you think SEC_FRAGS is better, I'm
fine with it. I'd make it SEC_XDP_FRAGS to make it more obvious it's
still XDP-specific (there are no plans to extend it to non-XDP,
right?).

But whichever way, it's internal implementation detail and pretty
small one at that, so I don't care much.

  [0] https://lore.kernel.org/bpf/CAEf4BzbfDvH5CYNsWg9Dx7JcFEp4jNmNRR6H-6sJEUxDSy1zZw@mail.gmail.com/