On Aug 17, 2009, at 11:41 AM, Matt Sergeant wrote:
>
> Kernels will fflush when a file handle is closed
Not according to Ted Ts'o (creator of the Ext2/3/4 filesystems). See,
for example, the extensive discussions of this at
http://thunk.org/tytso/blog/2009/03/12/delayed-allocation-and-the-zero-length-file-problem/
http://thunk.org/tytso/blog/2009/03/15/dont-fear-the-fsync/
Ted says that it is widely believed among programmers that close()
will sync a file, but in fact nothing in POSIX requires this and in
fact Linux does not do it. Some hacks were added to ext4 in the
2.6.30 kernel release to mitigate the damage following a power loss
when programs fail to fsync() prior to close(). But everybody agrees
those changes are an ugly hack.
In POSIX, the bottom line is this: The *only* way to force data to
oxide is to call sync() or fsync(). Some kernels and/or some
filesystems might sync at other times, but it is not something that
you can rely on.
D. Richard Hipp
[email protected]
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