linux-kernel - Re: Direct i/o changes break all non-GPL file systems

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Date:	Fri, 10 Feb 2012 21:19:48 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	Anton Altaparmakov <anton@...era.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Szabolcs Szakacsits <szaka@...era.com>,
	Janne Kalliom?ki <janne@...era.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Direct i/o changes break all non-GPL file systems

On Fri, Feb 10, 2012 at 11:28:27AM -0800, Linus Torvalds wrote:
> On Tue, Feb 7, 2012 at 5:51 PM, Andreas Dilger <adilger@...ger.ca> wrote:
> >
> > This doesn't affect me directly, since Lustre is itself a GPL filesystem,
> > but it does seem a bit harsh for such a minor amount of functionality.
> 
> It also wasn't documented in the commit or apparently even intentional.
> 
> > Looking at inode_dio_wait(), there isn't anything in there that couldn't
> > be implemented without using that GPL-only symbol export. ?Both inode_dio_wait()
> > and __inode_dio_wait() use only functions that are themselves EXPORT_SYMBOL()
> > (i.e. not GPL-only) and locally accessible structures (inode->i_dio_count
> > and inode->i_state), so I don't see any benefit or reason in making
> > inode_dio_wait() itself GPL.
> 
> Yes. I suspect we should just remove the _GPL part. Christoph, Al?

I'm all for it; TBH, I simply missed _GPL on those back then.  As far as I'm
concerned, there are 3 cases:
	1) it's a part of general-purpose API and it does make sense for
modules; use EXPORT_SYMBOL
	2) it's a kernel-internal thing that is not used by in-tree modules
and should not be used by any modules; don't export it at all
	3) it's a layering violation that unfortunately still is needed for
an in-tree module.  The *only* case where I'd consider EXPORT_SYMBOL_GPL
borderline useful, as a bad proxy for EXPORT_SYMBOL_DONT_USE_OUT_OF_TREE.

It's Christoph's code, though, so I'm not happy with just going ahead and
ripping that _GPL off those exports.  Christoph?

And folks, for the future, do not use ..._GPL on VFS exports unless you have
a damn good reason to discourage the use in out-of-tree modules in general.
Which needs to be clearly documented.
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