netdev - Re: [PATCH bpf-next 3/3] samples: bpf: refactor XDP kern program maps with BTF-defined map

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Date:   Fri, 9 Oct 2020 11:25:33 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Xdp <xdp-newbies@...r.kernel.org>
Subject: Re: [PATCH bpf-next 3/3] samples: bpf: refactor XDP kern program maps
 with BTF-defined map

On Fri, Oct 9, 2020 at 9:04 AM Daniel T. Lee <danieltimlee@...il.com> wrote:
>
> Most of the samples were converted to use the new BTF-defined MAP as
> they moved to libbpf, but some of the samples were missing.
>
> Instead of using the previous BPF MAP definition, this commit refactors
> xdp_monitor and xdp_sample_pkts_kern MAP definition with the new
> BTF-defined MAP format.
>
> Also, this commit removes the max_entries attribute at PERF_EVENT_ARRAY
> map type. The libbpf's bpf_object__create_map() will automatically
> set max_entries to the maximum configured number of CPUs on the host.
>
> Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> ---
>  samples/bpf/xdp_monitor_kern.c     | 60 +++++++++++++++---------------
>  samples/bpf/xdp_sample_pkts_kern.c | 14 +++----
>  samples/bpf/xdp_sample_pkts_user.c |  1 -
>  3 files changed, 36 insertions(+), 39 deletions(-)
>

[...]

> --- a/samples/bpf/xdp_sample_pkts_kern.c
> +++ b/samples/bpf/xdp_sample_pkts_kern.c
> @@ -5,14 +5,12 @@
>  #include <bpf/bpf_helpers.h>
>
>  #define SAMPLE_SIZE 64ul
> -#define MAX_CPUS 128
> -
> -struct bpf_map_def SEC("maps") my_map = {
> -       .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> -       .key_size = sizeof(int),
> -       .value_size = sizeof(u32),
> -       .max_entries = MAX_CPUS,
> -};
> +
> +struct {
> +       __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +       __type(key, int);
> +       __type(value, u32);


this actually will generate unnecessary libbpf warnings, because
PERF_EVENT_ARRAY doesn't support BTF types for key/value. So use
__uint(key_size, sizeof(int)) and __uint(value_size, sizeof(u32))
instead.

> +} my_map SEC(".maps");
>
>  SEC("xdp_sample")
>  int xdp_sample_prog(struct xdp_md *ctx)
> diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
> index 991ef6f0880b..4b2a300c750c 100644
> --- a/samples/bpf/xdp_sample_pkts_user.c
> +++ b/samples/bpf/xdp_sample_pkts_user.c
> @@ -18,7 +18,6 @@
>
>  #include "perf-sys.h"
>
> -#define MAX_CPUS 128
>  static int if_idx;
>  static char *if_name;
>  static __u32 xdp_flags = XDP_FLAGS_UPDATE_IF_NOEXIST;
> --
> 2.25.1
>