On Thu, 23 Aug 2001, Dr Andrew C Aitchison wrote:
> I followed the sample fix http://www.and.org/exim-3.31-dirfsync.patch
> well enough to make some guesses.
>
> While fsync flushes the file to disk and rename is atomic from the
> point of view of other processes, I summize that rename is *not* atomic
> below the filesystem level. There is a window during which the
> all process will be told that the rename has happened, but the
> disk thinks that the rename has not.
Yes, I think I've come to a similar conclusion.
The posted fix is, sigh, Linux-specific. It uses O_DIRECTORY. The man
page on RedHat Linux says this:
O_DIRECTORY
If pathname is not a directory, cause the open to
fail. This flag is Linux-specific, and was added
in kernel version 2.1.126, to avoid denial-of-ser
vice problems if opendir(3) is called on a FIFO or
tape device, but should not be used outside of the
implementation of opendir.
So in fact, the posted fix is illegal!
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
