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Date:   Wed, 29 Apr 2020 19:12:28 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next v1 17/19] tools/bpf: selftests: add iterator
 programs for ipv6_route and netlink

On Mon, Apr 27, 2020 at 1:18 PM Yonghong Song <yhs@...com> wrote:
>
> Two bpf programs are added in this patch for netlink and ipv6_route
> target. On my VM, I am able to achieve identical
> results compared to /proc/net/netlink and /proc/net/ipv6_route.
>
>   $ cat /proc/net/netlink
>   sk               Eth Pid        Groups   Rmem     Wmem     Dump  Locks    Drops    Inode
>   000000002c42d58b 0   0          00000000 0        0        0     2        0        7
>   00000000a4e8b5e1 0   1          00000551 0        0        0     2        0        18719
>   00000000e1b1c195 4   0          00000000 0        0        0     2        0        16422
>   000000007e6b29f9 6   0          00000000 0        0        0     2        0        16424
>   ....
>   00000000159a170d 15  1862       00000002 0        0        0     2        0        1886
>   000000009aca4bc9 15  3918224839 00000002 0        0        0     2        0        19076
>   00000000d0ab31d2 15  1          00000002 0        0        0     2        0        18683
>   000000008398fb08 16  0          00000000 0        0        0     2        0        27
>   $ cat /sys/fs/bpf/my_netlink
>   sk               Eth Pid        Groups   Rmem     Wmem     Dump  Locks    Drops    Inode
>   000000002c42d58b 0   0          00000000 0        0        0     2        0        7
>   00000000a4e8b5e1 0   1          00000551 0        0        0     2        0        18719
>   00000000e1b1c195 4   0          00000000 0        0        0     2        0        16422
>   000000007e6b29f9 6   0          00000000 0        0        0     2        0        16424
>   ....
>   00000000159a170d 15  1862       00000002 0        0        0     2        0        1886
>   000000009aca4bc9 15  3918224839 00000002 0        0        0     2        0        19076
>   00000000d0ab31d2 15  1          00000002 0        0        0     2        0        18683
>   000000008398fb08 16  0          00000000 0        0        0     2        0        27
>
>   $ cat /proc/net/ipv6_route
>   fe800000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001       lo
>   fe80000000000000c04b03fffe7827ce 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   ff000000000000000000000000000000 08 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000003 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   $ cat /sys/fs/bpf/my_ipv6_route
>   fe800000000000000000000000000000 40 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000001 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>   00000000000000000000000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000003 00000000 80200001       lo
>   fe80000000000000c04b03fffe7827ce 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000002 00000000 80200001     eth0
>   ff000000000000000000000000000000 08 00000000000000000000000000000000 00 00000000000000000000000000000000 00000100 00000003 00000000 00000001     eth0
>   00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200       lo
>
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  .../selftests/bpf/progs/bpf_iter_ipv6_route.c | 69 +++++++++++++++++
>  .../selftests/bpf/progs/bpf_iter_netlink.c    | 77 +++++++++++++++++++
>  2 files changed, 146 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_netlink.c
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c b/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c
> new file mode 100644
> index 000000000000..bed34521f997
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_ipv6_route.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Facebook */
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include <bpf/bpf_endian.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +extern bool CONFIG_IPV6_SUBTREES __kconfig __weak;
> +
> +#define        RTF_GATEWAY             0x0002
> +#define IFNAMSIZ               16
> +#define fib_nh_gw_family        nh_common.nhc_gw_family
> +#define fib_nh_gw6              nh_common.nhc_gw.ipv6
> +#define fib_nh_dev              nh_common.nhc_dev
> +
> +SEC("iter/ipv6_route")
> +int dump_ipv6_route(struct bpf_iter__ipv6_route *ctx)
> +{
> +       static const char fmt1[] = "%pi6 %02x ";
> +       static const char fmt2[] = "%pi6 ";
> +       static const char fmt3[] = "00000000000000000000000000000000 ";
> +       static const char fmt4[] = "%08x %08x %08x %08x %8s\n";
> +       static const char fmt5[] = "%08x %08x %08x %08x\n";
> +       static const char fmt7[] = "00000000000000000000000000000000 00 ";
> +       struct seq_file *seq = ctx->meta->seq;
> +       struct fib6_info *rt = ctx->rt;
> +       const struct net_device *dev;
> +       struct fib6_nh *fib6_nh;
> +       unsigned int flags;
> +       struct nexthop *nh;
> +
> +       if (rt == (void *)0)
> +               return 0;
> +
> +       fib6_nh = &rt->fib6_nh[0];
> +       flags = rt->fib6_flags;
> +
> +       /* FIXME: nexthop_is_multipath is not handled here. */
> +       nh = rt->nh;
> +       if (rt->nh)
> +               fib6_nh = &nh->nh_info->fib6_nh;
> +
> +       BPF_SEQ_PRINTF(seq, fmt1, &rt->fib6_dst.addr, rt->fib6_dst.plen);
> +
> +       if (CONFIG_IPV6_SUBTREES)
> +               BPF_SEQ_PRINTF(seq, fmt1, &rt->fib6_src.addr,
> +                              rt->fib6_src.plen);
> +       else
> +               BPF_SEQ_PRINTF0(seq, fmt7);

Looking at these examples, I think BPF_SEQ_PRINTF should just assume
that fmt argument is string literal and do:

static const char ___tmp_fmt[] = fmt;

inside that macro. So one can just do:

BPF_SEQ_PRINTF(seq, "Hello, world!\n");

or

BPF_SEQ_PRINTF(seq, "My awesome template %d ==> %s\n", id, some_string);

WDYT?

> +
> +       if (fib6_nh->fib_nh_gw_family) {
> +               flags |= RTF_GATEWAY;
> +               BPF_SEQ_PRINTF(seq, fmt2, &fib6_nh->fib_nh_gw6);
> +       } else {
> +               BPF_SEQ_PRINTF0(seq, fmt3);
> +       }
> +
> +       dev = fib6_nh->fib_nh_dev;
> +       if (dev)
> +               BPF_SEQ_PRINTF(seq, fmt4, rt->fib6_metric,
> +                              rt->fib6_ref.refs.counter, 0, flags, dev->name);
> +       else
> +               BPF_SEQ_PRINTF(seq, fmt4, rt->fib6_metric,
> +                              rt->fib6_ref.refs.counter, 0, flags);
> +
> +       return 0;
> +}

[...]

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