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Date: Mon, 30 Jul 2001 13:11:32 -0400
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From: Lawrence Greenfield <leg+@andrew.cmu.edu>
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To: Rik van Riel <riel@conectiva.com.br>,
        "Patrick J. LoPresti" <patl@cag.lcs.mit.edu>
Cc: linux-kernel@vger.kernel.org, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Chris Wedgwood <cw@f00f.org>, Chris Mason <mason@suse.com>
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Subject: Re: ext3-2.4-0.9.4
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   From: "Patrick J. LoPresti" <patl@cag.lcs.mit.edu>
   Date: 	30 Jul 2001 12:46:13 -0400

   > Besides BSD softupdates and the various journaling
   > filesystems which are in use on other Unixen also
   > don't provide the 4.3BSD solution any more ...

   This surprises me if it is true; do you have a reference?  And what
   mechanism *do* the modern BSDs provide to commit metadata changes to
   disk?

BSD softupdates allows you to call fsync() on the file, and this will
sync the directories all the way up to the root if necessary.

Thus BSD fsync() actually guarantees that when it returns, the file
(and all of it's filenames) will survive a reboot.

Sendmail does:
fd = open(tmp)
write(fd)
fsync(fd)
rename(tmp, final)
fsync(fd)

Cyrus IMAP does:
fd = open(tmp)
write(fd)
fsync(fd)
link(tmp, final1)
link(tmp, final2)
link(tmp, final3)
fsync(fd)
close(fd)
unlink(tmp)

The idea that Linux fsync() doesn't actually make the file survive
reboots is pretty ridiculous.

Larry


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