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

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Message-Id: <92291682-5422-4AE2-9608-97775603E7FD@tuxera.com>
Date:	Wed, 8 Feb 2012 00:07:15 +0000
From:	Anton Altaparmakov <anton@...era.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>
Cc:	Szabolcs Szakacsits <szaka@...era.com>,
	Janne Kalliomäki <janne@...era.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Direct i/o changes break all non-GPL file systems

Hi Linus, Andrew, Christoph,

With kernel 3.1, Christoph removed i_alloc_sem and replaced it with calls (namely inode_dio_wait() and inode_dio_done()) which are EXPORT_SYMBOL_GPL() thus they cannot be used by non-GPL file systems and further inode_dio_wait() was pushed from notify_change() into the file system ->setattr() method but no non-GPL file system can make this call.

That means non-GPL file systems cannot exist any more unless they do not use any VFS functionality related to reading/writing as far as I can tell or at least as long as they want to implement direct i/o.

What are commercial file systems meant to do now?

For example Tuxera exFAT uses the generic write code which means that read/write use the generic direct_IO functions however Tuxera exFAT's setattr() method cannot call inode_dio_wait() and there are places where exfat_truncate() is called directly with i_alloc_sem held and now this needs to be replaced with calls to inode_dio_wait() but we cannot do that as the function is GPL only.

Previously when APIs have been changed that were accessible to non-GPL modules it was made sure those APIs remained that way but this does not appear to be the case here.

Do all non-GPL file systems now really have to re-implement the entire read-write code paths for themselves for the sake of two GPL only exports in the direct i/o code?  That seems a bit harsh!

Have I missed something?  If not would you accept a patch to change the two needed GPL only symbols into EXPORT_SYMBOL() ones?

Thanks a lot in advance!

Best regards,

	Anton
-- 
Anton Altaparmakov <anton at tuxera.com> (replace at with @)
Senior Kernel Developer, Tuxera Inc., http://www.tuxera.com/
Linux NTFS maintainer, http://www.linux-ntfs.org/

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