From: "Ethy H. Brito" <ethy.brito@inexo.com.br>
To: Ivan Koveshnikov <ikoveshnik@gmail.com>
Cc: "xdp-newbies@vger.kernel.org" <xdp-newbies@vger.kernel.org>
Subject: Re: bpf_debug output
Date: Thu, 15 Jul 2021 16:25:53 -0300 [thread overview]
Message-ID: <20210715162553.3e151bae@babalu> (raw)
In-Reply-To: <CAHQrGVPbu8WVEaGWV1ytuOwx=-yam0OHD2fpOQdVVHTUz9F2GQ@mail.gmail.com>
On Wed, 14 Jul 2021 22:06:48 +0500
Ivan Koveshnikov <ikoveshnik@gmail.com> wrote:
> Hi Ethy,
Hi Ivan (and others behind the bushes)
>
> Correct. The output is available via file
> `/sys/kernel/debug/tracing/trace_pipe`. There are other helper
> programs that can also read it, like `bpftool prog tracelog` or `tc
> exec bpf dbg`.
>
> But you need to pay attention, what you're trying to print, since
> `bpf_printk()` supports much fewer formats than usual `printk()`. I.e.
> only `%d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %s`
> conversion specifiers are allowed. If an unsupported specifier is
> spotted, the string is silently dropped and never appears in trace
> log.
Very useful info.
I couldn't see my logs just because of this: unsupported format.
Now it is OK.
>
> Here you can find some examples:
> https://github.com/xdp-project/xdp-tutorial/tree/master/tracing03-xdp-debug-print
Thanx
Regards
Ethy
>
>
> Best regards,
> Ivan Koveshnikov
>
> On Wed, 14 Jul 2021 at 08:08, Ethy H. Brito <ethy.brito@inexo.com.br> wrote:
> >
> >
> > Hi!
> >
> > I am working on some minor modifications in xdp-cpumap-tc to accommodate NAT at WAN side.
> > But the things are not working as expected.
> >
> > How can bpf_debug be used to help debugging?
> >
> > I read that its output ends-up in /sys/kernel/debug/tracing/trace_pipe.
> > But how can it be read?
> > I tried "cat trace_pipe" but this produced no output whatsoever.
> >
> > Any hints will be appreciated.
> >
> > Thanx
> >
> > Regards
> >
> > Ethy
--
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prev parent reply other threads:[~2021-07-15 19:28 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 3:08 bpf_debug output Ethy H. Brito
2021-07-14 17:06 ` Ivan Koveshnikov
2021-07-15 19:25 ` Ethy H. Brito [this message]
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