linux-kernel - Re: [PATCH 1/3] tracing: add __print

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Date:	Mon, 18 May 2009 13:38:54 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH 1/3] tracing: add __print_flags for events

On Fri, May 15, 2009 at 05:03:43PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Developers have been asking for the ability in the ftrace event tracer
> to display names of bits in a flags variable.
> 
> Instead of printing out c2, it would be easier to read FOO|BAR|GOO,
> assuming that FOO is bit 1, BAR is bit 6 and GOO is bit 7.
> 
> Some examples where this would be useful are the state flags in a context
> switch, kmalloc flags, and even permision flags in accessing files.
> 
> I included Frederic Weisbecker's idea of using a mask instead of bits,
> thus we can output GFP_KERNEL instead of GPF_WAIT|GFP_IO|GFP_FS.
> 
> I also included Li Zefan's idea of allowing the caller of __print_flags
> to add their own delimiter (or no delimiter) where we can get for
> file permissions rwx instead of r|w|x.

Looks good to me.

Some small comments:

 - __print_flags might be a little to generic.  What about trace_print_flags?
 - some documentation would help.  I can submit a patch to the
   trave_events sample module to make use of it once this patch is
   merged.
 - Maybe passing an array instead of a list of flag/value pairs would be
   a tad cleaner?  That would get rid of all the varargs mess and allow
   to declare that array next to the flags so get less easily out of
   sync.

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