> fraioli@dg-rtp.dg.com (Marc J. Fraioli) writes:
> > I'm looking at the docs for CMU's cygnus IMAP server, and came
> > across the following warning in a README:
> > [...]
> > What is the reason for this?
>
> The ext2 filesystem performs directory updates asynchronously. When
> the IMAP server (or sendmail) is given a message, it will create a
> file for it, write out the contents, and fsync() it before informing
> the sender that it has accepted responsibility for the message.
>
> However, the fsync() doesn't mean a hill of beans if the directory
> entry for the file doesn't get committed to disk. If the machine
You are saying that fsync() violates the POSIX requirements. It seems
that recent POSIX has a relaxed fsync() that "only writes essential
data" to the disk. I can't remember the syscall right now. I'm rather
sure that Ted knows about it.
If fsync is broken, shouldn't it be fixed before 2.0?
> crashes before that buffer gets flushed, the message gets lost. There
> is no way the application can commit the directory change short of
> calling sync().
>
> Similarly, there are cases where the server databases can become
> inconsistent if rename() calls don't get committed to disk. There's a
> *lot* of open()/writev()/fsync()/rename() sequences in the code.
>
> These server applications absolutely depend on synchronous directory
> updates. So the directories for their databases have to be marked
> with the synchronous attribute.
>
> --
> _.John G. Myers Internet: jgm+@CMU.EDU
> LoseNet: ...!seismo!ihnp4!wiscvm.wisc.edu!give!up
------------
Ulrich Windl Klinikum der Universitaet Regensburg
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