Messages in this thread | | | Date | Tue, 19 Aug 2008 17:56:10 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: vfat BKL/lock_super regression in v2.6.26-rc3-g8f59342 |
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On Tue, 19 Aug 2008, Linus Torvalds wrote: > > But I don't know exactly what the timeout should be, though (although I > suspect that it should involve _ignoring_ non-data writes like the atime > updates, and trigger a timeout on data writes so that when you actually > write a file, you'll know that the sync will happen within five seconds of > you having finished the write or whatever).
.. and by "finished the write" I mean "closed the file", not "end of write() system call". Ie it's one of those things where it really doesn't mostly make much sense to try to give any kinds of flush guarantees until the user has basically shown that he's all done with writing.
If you have something like removable media, and you actually remove it while you have a "cp -R" in progress, it damn well won't matter whether we were synchronous or not. But if you remove it after the "cp" has actually finished, it's a lot more understandable if somebody expects it to be on disk.
So one thing we could perhaps consider is to make FAT in particular consider "sync" mounts to be about open/close consistency, not about per-write-system-call consistency. So the "close()" wouldn't return until the file is on disk, but we wouldn't force a synchronous rewrite the inode or the file allocation table thousands of times just because the file was big.
FAT really is kind of different. I suspect we could just change what "sync" means for it. But it would probably be good to have a VFS-level notion of open-close consistency. It is, after all, what NFS is already supposed to give you, so there is precedence for that being a useful IO serialization model.
Al, what do you think?
Linus
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