linux-kernel - Re: [PATCH RFC v4 net-next 23/26] samples: bpf: elf file loader

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Message-ID: <CAE40pddG1e3Q8OZ8t5QQimGhHzS5FbqK3YuvKnFywEEoSUbGzQ@mail.gmail.com>
Date:	Thu, 14 Aug 2014 12:29:09 -0700
From:	Brendan Gregg <brendan.d.gregg@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v4 net-next 23/26] samples: bpf: elf file loader

On Wed, Aug 13, 2014 at 12:57 AM, Alexei Starovoitov <ast@...mgrid.com> wrote:
[...]
> +static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
> +{
> +       int fd, event_fd, err;
> +       char fmt[32];
> +       char path[256] = DEBUGFS;
> +
> +       fd = bpf_prog_load(BPF_PROG_TYPE_TRACING_FILTER, prog, size, license);
> +
> +       if (fd < 0) {
> +               printf("err %d errno %d\n", fd, errno);
> +               return fd;
> +       }

Minor suggestion: since this is sample code, I'd always print the bpf
log after this this printf() error message:

printf("%s", bpf_log_buf);

Which has helped me debug my eBPF programs, as will be the case for
anyone hacking on the examples. Or have a function for logdie(), if
the log buffer may be populated with useful messages from other error
paths as well.

Brendan
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