linux-kernel - Re: [PATCH 3/8] Add yaffs2 file system: guts code

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Message-Id: <201012071113.51408.manningc2@actrix.gen.nz>
Date:	Tue, 7 Dec 2010 11:13:51 +1300
From:	Charles Manning <manningc2@...rix.gen.nz>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 3/8] Add yaffs2 file system: guts code

On Tuesday 07 December 2010 01:55:43 Arnd Bergmann wrote:
> On Monday 06 December 2010, Charles Manning wrote:
> > On Wednesday 01 December 2010 11:23:53 you wrote:
> > > On Tuesday 30 November 2010 22:57:29 Charles Manning wrote:
> > > It would be better to reorder the functions in each file so that
> > > you don't need forward declarations. This generally makes reading
> > > the code easier because it is what people expect to see. It
> > > also makes it clearer where you have possible recursions in the code.
> >
> > Hmmm..
> > I too prefer minimal use of forward declaration.
> > Some of them are because I copied the layout of existing kernel code
> > which uses fwd declarations a lot. eg. fs/jffs2/dir.c  and many of the
> > examples in Rubini & Corbet.
>
> There is not much point in changing the legacy code that's already in
> the kernel, but let's try to keep it clean for new code. We have a lot
> of bad examples for coding style that we wouldn't merge these days.
>
> In this case, it should be an obvious change with no real downsides.

Arnd thanks for your input, I appreciate it immensely.

Is this objection to forward declarations just your personal taste or is this 
a real issue?

I can't find any references to forward declarations in any of the coding style 
docs. I would therefore expect it to be an issue of little consequence. 
Perhaps I did not look in the right places.

It is perhaps also worth considering that yaffs has been in use for 8 years 
and is more widely used than many of the file systems already in the kernel  
and thus, by some measures, does constitute legacy code.

>
> > > > +	T(YAFFS_TRACE_BUFFERS,
> > > > +	  (TSTR("Out of temp buffers at line %d, other held by lines:"),
> > > > +	   line_no));
> > > > +	for (i = 0; i < YAFFS_N_TEMP_BUFFERS; i++)
> > > > +		T(YAFFS_TRACE_BUFFERS,
> > > > +		  (TSTR(" %d "), dev->temp_buffer[i].line));
> > > > +
> > > > +	T(YAFFS_TRACE_BUFFERS, (TSTR(" " TENDSTR)));
> > >
> > > The tracing functions are rather obscure. I would recommend dropping
> > > them all for now, in order to get the code included.
> >
> > Yup that was a very ugly bunch of hackery to make WinCE unicode work.
> >
> > I think I can pull the var-arg-foo to replace these with
> >
> > yaffs_trace(YAFFS_TRACE_BUFFERS,
> > 	"Out of temp buffers at line %d, other held by lines:",line_no);
> > for (i = 0; i < YAFFS_N_TEMP_BUFFERS; i++)
> > 	yaffs_trace(YAFFS_TRACE_BUFFERS," %d ", dev->temp_buffer[i].line);
> > yaffs_trace(YAFFS_TRACE_BUFFERS, "\n");
> >
> > Would that be OK?
> >
> > I am loath to have to pull out useful code then plug it back in again.
>
> I don't think the yaffs_trace() function would be much better than the T()
> macro, I was talking more about the fact that you have your own nonstandard
> tracing infrastructure than the ugliness of the interface.
>
> The point of pulling it out now would be force you to rethink the
> tracing. If you think that you'd arrive at the same conclusion, just
> save the diff between the code with and without tracing so you can
> submit that patch again later.
>
> Having some sort of tracing is clearly useful, but it's also not essential
> for the basic yaffs2 operation. We want to keep a consistent way of
> presenting trace points across the kernel, so as long as you do it
> differently, your code is going to be viewed with some suspicion.
>
> Please have a look at how ext4, gfs2 and xfs do tracing.

Looking in Linus' tree, all of those contain custom tracing of the form I 
propose.

>
> > > At a later
> > > stage, you can add standard trace points.
> > >
> > > > +	return YMALLOC(dev->data_bytes_per_chunk);
> >
> > I'm getting rid of those..
> >
> > The reason for thew wrapping was to make portable code.
> >
> > I'm replacing these with kmalloc() and then providing kmalloc() which is
> > just a wrapped malloc() for non-Linux use.
>
> Ok, excellent!
>
> > I am hoping to reduce this to YCHAR, _Y() and maybe one or two others.
>
> Ok. Maybe rename YCHAR to ychar to make it stick out less, and add a
> comment to the definition why you need it then.

Can do.

Thanks.

-- Charles
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