netdev - Re: [PATCH net-next] samples/bpf: Fix map interation in xdp1

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Date:   Mon, 17 Oct 2022 09:27:57 -0700
From:   Song Liu <song@...nel.org>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, john.fastabend@...il.com,
        bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] samples/bpf: Fix map interation in xdp1_user

On Thu, Oct 13, 2022 at 2:01 PM Gerhard Engleder
<gerhard@...leder-embedded.com> wrote:
>
> BPF map iteration in xdp1_user results in endless loop without any
> output, because the return value of bpf_map_get_next_key() is checked
> against the wrong value.
>
> Other call locations of bpf_map_get_next_key() check for equal 0 for
> continuing the iteration. xdp1_user checks against unequal -1. This is
> wrong for a function which can return arbitrary negative errno values,
> because a return value of e.g. -2 results in an endless loop.
>
> With this fix xdp1_user is printing statistics again:
> proto 0:          1 pkt/s
> proto 0:          1 pkt/s
> proto 17:     107383 pkt/s
> proto 17:     881655 pkt/s
> proto 17:     882083 pkt/s
> proto 17:     881758 pkt/s
>
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>

Acked-by: Song Liu <song@...nel.org>

> ---
>  samples/bpf/xdp1_user.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/samples/bpf/xdp1_user.c b/samples/bpf/xdp1_user.c
> index ac370e638fa3..281dc964de8d 100644
> --- a/samples/bpf/xdp1_user.c
> +++ b/samples/bpf/xdp1_user.c
> @@ -51,7 +51,7 @@ static void poll_stats(int map_fd, int interval)
>
>                 sleep(interval);
>
> -               while (bpf_map_get_next_key(map_fd, &key, &key) != -1) {
> +               while (bpf_map_get_next_key(map_fd, &key, &key) == 0) {
>                         __u64 sum = 0;
>
>                         assert(bpf_map_lookup_elem(map_fd, &key, values) == 0);
> --
> 2.30.2
>