* bpf_debug output
@ 2021-07-14 3:08 Ethy H. Brito
2021-07-14 17:06 ` Ivan Koveshnikov
0 siblings, 1 reply; 3+ messages in thread
From: Ethy H. Brito @ 2021-07-14 3:08 UTC (permalink / raw)
To: xdp-newbies
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: bpf_debug output
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
0 siblings, 1 reply; 3+ messages in thread
From: Ivan Koveshnikov @ 2021-07-14 17:06 UTC (permalink / raw)
To: Ethy H. Brito; +Cc: xdp-newbies
Hi Ethy,
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.
Here you can find some examples:
https://github.com/xdp-project/xdp-tutorial/tree/master/tracing03-xdp-debug-print
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: bpf_debug output
2021-07-14 17:06 ` Ivan Koveshnikov
@ 2021-07-15 19:25 ` Ethy H. Brito
0 siblings, 0 replies; 3+ messages in thread
From: Ethy H. Brito @ 2021-07-15 19:25 UTC (permalink / raw)
To: Ivan Koveshnikov; +Cc: xdp-newbies
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
--
Ethy H. Brito /"\
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PGP key: http://www.inexo.com.br/~ethy/0xC3F222A0.asc
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