netdev - Re: [PATCH v21 bpf-next 18/23] libbpf: Add SEC name for xdp

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Date:   Sun, 9 Jan 2022 18:16:35 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Shay Agroskin <shayagr@...zon.com>,
        john fastabend <john.fastabend@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Saeed Mahameed <saeed@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        tirthendu.sarkar@...el.com,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH v21 bpf-next 18/23] libbpf: Add SEC name for xdp_mb programs

On Sun, Jan 9, 2022 at 7:05 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
>
> Introduce support for the following SEC entries for XDP multi-buff
> property:
> - SEC("xdp_mb/")
> - SEC("xdp_devmap_mb/")
> - SEC("xdp_cpumap_mb/")

Libbpf seemed to went with .<suffix> rule (e.g., fentry.s for
sleepable, seems like we'll have kprobe.multi or  something along
those lines as well), so let's stay consistent and call this "xdp_mb",
"xdp_devmap.mb", "xdp_cpumap.mb" (btw, is "mb" really all that
recognizable? would ".multibuf" be too verbose?). Also, why the "/"
part? Also it shouldn't be "sloppy" either. Neither expected attach
type should be optional.  Also not sure SEC_ATTACHABLE is needed. So
at most it should be SEC_XDP_MB, probably.

>
> Acked-by: Toke Hoiland-Jorgensen <toke@...hat.com>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  tools/lib/bpf/libbpf.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7f10dd501a52..c93f6afef96c 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -235,6 +235,8 @@ enum sec_def_flags {
>         SEC_SLEEPABLE = 8,
>         /* allow non-strict prefix matching */
>         SEC_SLOPPY_PFX = 16,
> +       /* BPF program support XDP multi-buff */
> +       SEC_XDP_MB = 32,
>  };
>
>  struct bpf_sec_def {
> @@ -6562,6 +6564,9 @@ 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 && (def & SEC_XDP_MB))
> +               opts->prog_flags |= BPF_F_XDP_MB;

I'd say you don't even need SEC_XDP_MB flag at all, you can just check
that prog->sec_name is one of "xdp.mb", "xdp_devmap.mb" or
"xdp_cpumap.mb" and add the flag. SEC_XDP_MB doesn't seem generic
enough to warrant a flag.

> +
>         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 +8605,11 @@ 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_devmap_mb/",       XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE | SEC_XDP_MB),
>         SEC_DEF("xdp_devmap/",          XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE),
> +       SEC_DEF("xdp_cpumap_mb/",       XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE | SEC_XDP_MB),
>         SEC_DEF("xdp_cpumap/",          XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE),
> +       SEC_DEF("xdp_mb/",              XDP, BPF_XDP, SEC_ATTACHABLE_OPT | SEC_SLOPPY_PFX | SEC_XDP_MB),
>         SEC_DEF("xdp",                  XDP, BPF_XDP, SEC_ATTACHABLE_OPT | SEC_SLOPPY_PFX),
>         SEC_DEF("perf_event",           PERF_EVENT, 0, SEC_NONE | SEC_SLOPPY_PFX),
>         SEC_DEF("lwt_in",               LWT_IN, 0, SEC_NONE | SEC_SLOPPY_PFX),
> --
> 2.33.1
>