linux-kernel - Re: vfat BKL/lock_super regression in v2.6.26-rc3-g8f59342

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Message-ID: <20080820022712.GF28029@jukie.net>
Date:	Tue, 19 Aug 2008 22:27:12 -0400
From:	Bart Trojanowski <bart@...ie.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: vfat BKL/lock_super regression in v2.6.26-rc3-g8f59342

* Linus Torvalds <torvalds@...ux-foundation.org> [080819 20:56]:
> 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.

I was reading the vfat code, and it turns out that vfat has a "flush"
mount option.  Which is documented in the code (not in the manpage) as:

    struct fat_mount_options {
            ...
            unsigned
            ...
                     flush:1,         /* write things quickly */

Since that was very informative I looked at the usage.  It's used
in fat_file_release() to do almost what you describe.  But it seems to
be a best effort thing.  If my data doesn't hit the disk (or flash) in
HZ/10, then all bets are off.

-Bart

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