linux-kernel - Re: [PATCH 0/10] Add yaffs2 file system: Fifth patchset

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Date:	Sun, 20 Feb 2011 12:07:55 -0800
From:	Greg KH <greg@...ah.com>
To:	Charles Manning <manningc2@...rix.gen.nz>
Cc:	Ryan Mallon <ryan@...ewatersys.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 0/10] Add yaffs2 file system:  Fifth patchset

On Mon, Feb 21, 2011 at 06:25:08AM +1300, Charles Manning wrote:
> On Friday 18 February 2011 13:58:52 Greg KH wrote:
> > On Fri, Feb 18, 2011 at 01:55:04PM +1300, Ryan Mallon wrote:
> > > On 02/18/2011 01:43 PM, Mark Brown wrote:
> > > > On Thu, Feb 17, 2011 at 04:33:53PM -0800, Greg KH wrote:
> > > >> On Fri, Feb 18, 2011 at 12:01:50AM +0000, Mark Brown wrote:
> > > >>> For the proc stuff - for tracing stuff then tracepoints are likely to
> > > >>> be a good option if it's useful to people.
> > > >>
> > > >> Then use the in-kernel tracing functionality, don't roll your own. 
> > > >> And that is not in /proc, so it should be there for this filesystem
> > > >> either.
> > > >
> > > > That'd be the tracepoints I was mentioning, then...
> > >
> > > Are you suggesting that the yaffs_trace function should be replaced with
> > > tracepoints?
> > >
> > > yaffs_trace is basically just a wrapper around printk, which I suggested
> > > should be replaced with pr_debug so that it can be compiled out
> > > completely. Other drivers and filesystems have similar custom debugging
> > > functions.
> > >
> > > I haven't used tracepoints, but it seems like they are better suited to
> > > tracing specific events than as a general printk style debugging
> > > replacement?
> 
> The procfs is not used for tracing as , it is just one of the two ways 
> ofsetting a trace mask to  select what to trace (the other is to set a trace 
> mask).
> 
> eg.  echo +gc > /proc/yaffs
> 
> turns on the garbage collector tracing.
> 
> I will remove the /proc interface and write a userspace script to do the 
> equivalent.
> 
> Realtime selection of tracing is valuable. It allows you to set up a test case 
> with tracing disabled then select what you want to trace to get detail as you 
> run the test case

I agree, so please use the in-kernel tracing code which provides this
infrastructure for you.

> I still intend to keep the tracing printk-based tracing:
> 
> #define yaffs_trace(msk, fmt, ...) do { \
> 	if (yaffs_trace_mask & (msk)) \
> 		printk(KERN_DEBUG "yaffs: " fmt "\n", ##__VA_ARGS__); \
> } while (0)

No, please don't invent your own stuff like this, again, use the
in-kernel functionality provided for this.

thanks,

greg k-h
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