linux-kernel - Re: [PATCH 0/4] initramfs: remove sparse warnings

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Date:	Mon, 23 Aug 2010 23:59:43 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] initramfs: remove sparse warnings

2010-08-22 (일), 22:33 +0200, Arnd Bergmann:
> On Friday 20 August 2010 17:36:41 Namhyung Kim wrote:
> > 
> > 2010-08-20 (금), 13:00 +0100, Al Viro:
> > > No.  This code should NOT use the VFS guts, TYVM.  The whole fscking point
> > > is that this puppy is a sequence of plain vanilla syscalls, ideally run
> > > simply in userland thread.  We used to have a magical mystery shite in there
> > > and it had been a huge PITA.
> > 
> > So is it worth to work on removing the warnings like this patchset does?
> > Or else, how can I improve the code even a bit? Can you please give me a
> > direction?
> 
> It would be useful to add annotations in those places where they are
> obviously just missing but don't require adding __force.
> Even better would be patches that fix actual bugs found by sparse.
> 
> Simply throwing in extra __force arguments will just make people
> nervous, because it is often a sign of papering over a bug instead
> of fixing it, and warnings in the core kernel are there exactly
> because there is no easy correct fix for them.
> 
> Try producing patches that clean up the code and result in using
> fewer annotations and especially few __force where possible.
> Also, in places where you need __force, make sure that a person
> reading that code understands why it's needed and that the use is
> correct (or at least permissable).
> 
> One possible solution in this particular case would be to add
> helper functions like 
> 
> /* wrapper for sys_newlstat for use in the init code */
> static inline int kern_newlstat(const char * filename, struct stat * statbuf)
> {
> 	mm_segment_t fs = get_fs();
> 	int ret;
> 
> 	set_fs(KERNEL_DS);
> 	ret = sys_newlstat((const char __user __force*)filename,
> 			   (struct stat __user __force *)statbuf);
> 	set_fs(fs);
> 
> 	return ret;
> }
> 
> Such a function makes it clear that it can only accept a kernel pointer,
> and it documents how the conversion to a __user pointer happens (by
> calling set_fs).
> Then again, it adds some bloat, and it may encourage people to do the
> same thing in device drivers, which could be argued against such helpers.
> 
> In general, my recommendation would be to leave code alone if you can't
> come up with a patch that clearly improves it. There is enough
> bad code in the kernel that can use some help along the lines of
> your other patches, so you may want to focus on that.
> 
> 	Arnd

Thank you Arnd for the precious comments and advices. This really helps
me.

-- 
Regards,
Namhyung Kim


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