netdev - Re: [PATCH bpf-next] libbpf: fix BPF_LOG_BUF

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Message-ID: <20190419193206.gtu4ubv7aiu3xmge@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 19 Apr 2019 12:32:08 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     robert.mccabe@...kwellcollins.com
Cc:     netdev@...r.kernel.org, robertjmccabe@...il.com,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] libbpf: fix BPF_LOG_BUF_SIZE off-by-one error

On Fri, Apr 19, 2019 at 11:47:45AM -0500, robert.mccabe@...kwellcollins.com wrote:
> From: "McCabe, Robert J" <Robert.McCabe@...kwellcollins.com>
> 
> The BPF_PROG_LOAD condition for kernel version <= 5.1 is
> 
>    log->len_total > UINT_MAX >> 8 /* (16 * 1024 * 1024) - 1 */
> 
> Signed-off-by: rjmccabe3701 <robert.mccabe@...kwellcollins.com>
> ---
>  tools/lib/bpf/bpf.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index bc30783d1403..62d67caa7aea 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -92,7 +92,7 @@ struct bpf_load_program_attr {
>  #define MAPS_RELAX_COMPAT	0x01
> 
>  /* Recommend log buffer size */
> -#define BPF_LOG_BUF_SIZE (16 * 1024 * 1024) /* verifier maximum in kernels <= 5.1 */
> +#define BPF_LOG_BUF_SIZE ((16 * 1024 * 1024) - 1) /* verifier maximum in kernels <= 5.1 */

thanks. good catch.
please replace with (UINT32_MAX >> 8)

sending one patch was enough. no need to spam 5 times.