Val,
Maybe it is not only our (FS people) problem. We probably need to
bring the kernel people judge as ext2 and ext3 are the base Linux FS.
I add the kernel list for opinion.
/Sorin
On Wed, 14 Feb 2007 14:54:54 -0500, Valerie Henson
<[email protected]> wrote:
Just some quick notes on possible ways to fix the ext2 fsync bug that
eXplode found. Whether or not anyone will bother to implement it is
another matter.
Background: The eXplode file system checker found a bug in ext2 fsync
behavior. Do the following: truncate file A, create file B which
reallocates one of A's old indirect blocks, fsync file B. If you then
crash before file A's metadata is all written out, fsck will complete
the truncate for file A... thereby deleting file B's data. So fsync
file B doesn't guarantee data is on disk after a crash. Details:
http://www.stanford.edu/~engler/explode-osdi06.pdf
Two possible solutions I can think of:
* Rearrange order of duplicate block checking and fixing file size in
fsck. Not sure how hard this is. (Ted?)
* Keep a set of "still allocated on disk" block bitmaps that gets
flushed whenever a sync happens. Don't allocate these blocks.
Journaling file systems already have to do this.
-VAL
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