linux-kernel - Re: [PATCH v2 2/2] ftrace: printk formatting infrastructure

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Date:	Fri, 1 Aug 2008 12:53:17 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Randy Dunlap <randy.dunlap@...cle.com>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH v2 2/2] ftrace: printk formatting infrastructure


On Fri, 1 Aug 2008, Randy Dunlap wrote:

> On Fri, 01 Aug 2008 12:26:41 -0400 Steven Rostedt wrote:
> 
> > +/**
> > + * ftrace_printk - printf formatting in the ftrace buffer
> > + * @fmt - the printf format for printing.
> 
>     * @fmt: the printf format for printing
>     * @ip: <description>
> 
> > + *
> > + * Note: __ftrace_printk is an internal function for ftrace_printk and
> > + *       the @ip is passed in via the ftrace_printk macro.

The above note actually explains this ;-)

Should I move the description to the ftrace_printk macro?

In include/linux/ftrace.h you see:

#ifdef CONFIG_TRACING
[...]
# define ftrace_printk(x...) __ftrace_printk(_THIS_IP_, x)
extern int
__ftrace_printk(unsigned long ip, const char *fmt, ...)
        __attribute__ ((format (printf, 2, 3)));
#else
[...]
static inline int
ftrace_printk(const char *fmt, ...) __attribute__ ((format (printf, 1, 
0)))
{
        return 0;
}
#endif

The true API is ftrace_printk(const char *fmt) and the __ftrace_printk
version should not be used.

Do you still think I should document the @ip?

I could also just remove the passing of _THIS_IP_ and use _RET_IP_ 
inside of ftrace_printk but the _THIS_IP_ seems to be more accurate 
especially when we have stack unwinding returns.

-- Steve



> > + *
> > + * This function allows a kernel developer to debug fast path sections
> > + * that printk is not appropriate for. By scattering in various
> > + * printk like tracing in the code, a developer can quickly see
> > + * where problems are occurring.
> > + *
> > + * This is intended as a debugging tool for the developer only.
> > + * Please reframe from leaving ftrace_printks scattered around in
> > + * your code.
> > + */
> > +int __ftrace_printk(unsigned long ip, const char *fmt, ...)
> > +{
> 
> 
> ---
> ~Randy
> Linux Plumbers Conference, 17-19 September 2008, Portland, Oregon USA
> http://linuxplumbersconf.org/
> 
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