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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Martynas Pumputis <m@lambda.lt>
Cc: David Ahern <dsahern@gmail.com>,
	Networking <netdev@vger.kernel.org>,
	Hangbin Liu <haliu@redhat.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH iproute2] libbpf: fix attach of prog with multiple sections
Date: Thu, 22 Jul 2021 21:01:43 -0700	[thread overview]
Message-ID: <CAEf4BzZCKHTA4o4ShmT_-THuT_mb7nwSkzG9OjeYVLPSzq4gmQ@mail.gmail.com> (raw)
In-Reply-To: <a68f1e05-e9c7-595e-23e9-6f02a3a209de@lambda.lt>

On Wed, Jul 21, 2021 at 8:25 AM Martynas Pumputis <m@lambda.lt> wrote:
>
>
>
> On 7/21/21 4:59 PM, David Ahern wrote:
> > On 7/21/21 8:47 AM, Martynas Pumputis wrote:
> >>>> diff --git a/lib/bpf_libbpf.c b/lib/bpf_libbpf.c
> >>>> index d05737a4..f76b90d2 100644
> >>>> --- a/lib/bpf_libbpf.c
> >>>> +++ b/lib/bpf_libbpf.c
> >>>> @@ -267,10 +267,12 @@ static int load_bpf_object(struct bpf_cfg_in *cfg)
> >>>>           }
> >>>>
> >>>>           bpf_object__for_each_program(p, obj) {
> >>>> +               bool prog_to_attach = !prog && cfg->section &&
> >>>> +                       !strcmp(get_bpf_program__section_name(p),
> >>>> cfg->section);
> >>>
> >>> This is still problematic, because one section can have multiple BPF
> >>> programs. I.e., it's possible two define two or more XDP BPF programs
> >>> all with SEC("xdp") and libbpf works just fine with that. I suggest
> >>> moving users to specify the program name (i.e., C function name
> >>> representing the BPF program). All the xdp_mycustom_suffix namings are
> >>> a hack and will be rejected by libbpf 1.0, so it would be great to get
> >>> a head start on fixing this early on.
> >>
> >> Thanks for bringing this up. Currently, there is no way to specify a
> >> function name with "tc exec bpf" (only a section name via the "sec"
> >> arg). So probably, we should just add another arg to specify the
> >> function name.
> >>
> >> It would be interesting to hear thoughts from iproute2 maintainers
> >> before fixing this.
> >
> > maintaining backwards compatibility is a core principle for iproute2. If
> > we know of a libbpf change is going to cause a breakage then it is best
> > to fix it before any iproute2 release is affected.
> >
>
> Just to avoid any confusion (if there is any), the required change we
> are discussing doesn't have anything to do with my fix.
>
> To set the context, the motivation for unifying section names is
> documented and discussed in "Stricter and more uniform BPF program
> section name (SEC()) handling" of [1].
>
> Andrii: is bpftool able to load programs with multiple sections which
> are named the same today?
>

I'm not familiar with those parts of bpftool, I've never used
bpftool's command to load BPF programs. Please go check the code.

>
> [1]:
> https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY/edit#

  reply	other threads:[~2021-07-23  4:04 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-05 12:43 Martynas Pumputis
2021-07-06  2:44 ` Hangbin Liu
2021-07-20 20:27 ` Andrii Nakryiko
2021-07-21 14:47   ` Martynas Pumputis
2021-07-21 14:59     ` David Ahern
2021-07-21 15:27       ` Martynas Pumputis
2021-07-23  4:01         ` Andrii Nakryiko [this message]
2021-07-23  4:41     ` Hangbin Liu
2021-07-23  4:51       ` Andrii Nakryiko
2021-07-23  7:55         ` Hangbin Liu
2021-07-23 16:09           ` Andrii Nakryiko
2021-07-24  8:12             ` Hangbin Liu
2021-07-24  0:12         ` David Ahern
2021-07-24  0:25           ` Andrii Nakryiko
2021-07-26 13:58             ` David Ahern
2021-07-26 15:13               ` Andrii Nakryiko
2021-07-27  2:51                 ` David Ahern
2021-07-27 19:05                   ` Andrii Nakryiko

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