Direct i/o changes break all non-GPL file systems
From: Anton Altaparmakov
Date: Tue Feb 07 2012 - 19:07:27 EST
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!
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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