netdev - Re: [PATCH] lib/bpf: Fix btf_load error lead to enable debug log

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Date:   Fri, 30 Jul 2021 11:40:28 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Feng zhou <zhoufeng.zf@...edance.com>
Cc:     Networking <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        kuznet@....inr.ac.ru, duanxiongchun@...edance.com,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        chenzhuowen.simon@...edance.com
Subject: Re: [PATCH] lib/bpf: Fix btf_load error lead to enable debug log

On Wed, Jul 28, 2021 at 9:55 PM Feng zhou <zhoufeng.zf@...edance.com> wrote:
>
> From: Feng Zhou <zhoufeng.zf@...edance.com>
>
> Use tc with no verbose, when bpf_btf_attach fail,
> the conditions:
> "if (fd < 0 && (errno == ENOSPC || !ctx->log_size))"
> will make ctx->log_size != 0. And then, bpf_prog_attach,
> ctx->log_size != 0. so enable debug log.
> The verifier log sometimes is so chatty on larger programs.
> bpf_prog_attach is failed.
> "Log buffer too small to dump verifier log 16777215 bytes (9 tries)!"
>
> BTF load failure does not affect prog load. prog still work.
> So when BTF/PROG load fail, enlarge log_size and re-fail with
> having verbose.
>
> Signed-off-by: Feng Zhou <zhoufeng.zf@...edance.com>
> ---

This seems to be targeted against iproute2? It would be good to
specify that as [PATCH iproute2] or something.


>  lib/bpf_legacy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/bpf_legacy.c b/lib/bpf_legacy.c
> index 8a03b9c2..d824388c 100644
> --- a/lib/bpf_legacy.c
> +++ b/lib/bpf_legacy.c
> @@ -1531,7 +1531,7 @@ retry:
>                  * into our buffer. Still, try to give a debuggable error
>                  * log for the user, so enlarge it and re-fail.
>                  */
> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
> +               if (fd < 0 && errno == ENOSPC) {
>                         if (tries++ < 10 && !bpf_log_realloc(ctx))
>                                 goto retry;
>
> @@ -2069,7 +2069,7 @@ retry:
>         fd = bpf_btf_load(ctx->btf_data->d_buf, ctx->btf_data->d_size,
>                           ctx->log, ctx->log_size);
>         if (fd < 0 || ctx->verbose) {
> -               if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
> +               if (fd < 0 && errno == ENOSPC) {
>                         if (tries++ < 10 && !bpf_log_realloc(ctx))
>                                 goto retry;
>
> --
> 2.11.0
>