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

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Date:	Fri, 1 Aug 2008 10:52:55 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 12:53:17 -0400 (EDT) Steven Rostedt wrote:

> 
> 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 ;-)

I read that.

> Should I move the description to the ftrace_printk macro?

Probably.

> 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?

Just move the kernel-doc to the macro then.

> 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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