linux-kernel - Re: [PATCH] mctp i2c: Add rx trace

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Date: Thu, 30 May 2024 16:42:12 +0800
From: Jeremy Kerr <jk@...econstruct.com.au>
To: Tal Yacobi <talycb8@...il.com>
Cc: matt@...econstruct.com.au, rostedt@...dmis.org, mhiramat@...nel.org, 
	mathieu.desnoyers@...icios.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] mctp i2c: Add rx trace

Hi Tal,

> > > mctp-i2c rx implementation doesn't call
> > > __i2c_transfer which calls the i2c reply trace function.
> > 
> > No, but we can trace the i2c rx path through the trace_i2c_slave
> > tracepoint. It is a little messier than tracing trace_i2c_write,
> > but
> > has been sufficient with the debugging I've needed in the past.
> 
> Oh, I missed that.
> I had to test it with an older kernel without i2c_slave tracing
> so I looked only at the regular i2c and mctp trace paths.

OK! That tracepoint was (coincidentally) added in 5.18, same as the
MCTP-over-i2c transport. So we should have coverage for both features
on upstream kernels, at least.

> > > Add an mctp_reply trace function that will be used instead.
> > 
> > Can you elaborate a little on what you were/are looking to inspect
> > here? (mainly: which packet fields are you interested in?) That
> > will
> > help to determine the best approach here.
> 
> Sure, I basically wanted to trace the i2c packet buffer in a simple
> way.

OK - did you specifically need the i2c transport headers? Since the
MCTP interfaces are regular net devices, the easiest way to trace
generic MCTP transfers is generally via a packet capture (tcpdump,
wireshark, etc).

Cheers,


Jeremy