[Lustre-devel] Flush on file close

[Nicolas Williams <Nicolas.Williams@oracle.com>]

POSIX behavior is that close(2) can fail, so if you care, you should
check its error status.  POSIX behavior is also that close(2) doesn't
imply an fsync(2) (much less a sync(2)).

NFS clients implement fsync(2)-on-close, but that's another story.

However, when writes deferred at close(2) time fail on a local
filesystem...  chances are that subsequent I/O will just fail.  Or at
least that's probably what many users will expect.  But does POSIX
require that?  I don't have it handy, but I'm pretty sure the answer is
"no".  With Lustre we could also have a close(2) whose deferred writes
fail long after the process that could handle the failure is gone.

Databases and so on should always fsync(2) when they need to ensure
consistent on-disk state.  Many apps that write(2) don't need to
fsync(2) (think of writes to log files).

Nico
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