From owner-freebsd-hackers  Tue Feb  6 11:20:59 2001
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Date: Tue, 6 Feb 2001 11:20:39 -0800 (PST)
From: Matt Dillon <dillon@earth.backplane.com>
Message-Id: <200102061920.f16JKdN64467@earth.backplane.com>
To: Mike Silbersack <silby@silby.com>
Cc: Andre Oppermann <oppermann@monzoon.net>,
	Poul-Henning Kamp <phk@critter.freebsd.dk>,
	Charles Randall <crandall@matchlogic.com>,
	Dan Phoenix <dphoenix@bravenet.com>,
	Alfred Perlstein <bright@wintelcom.net>,
	Jos Backus <josb@cncdsl.com>, <freebsd-hackers@FreeBSD.ORG>
Subject: Re: soft updates and qmail (RE: qmail IO problems)
References:  <Pine.BSF.4.31.0102061305430.15212-100000@achilles.silby.com>
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:On Tue, 6 Feb 2001, Matt Dillon wrote:
:
:>     I did a quick search of the qmail site but couldn't find an email
:>     address to report the FAQ issue to.  If QMail calls fsync() in a
:>     reasonable manner, then softupdates is perfectly safe and the QMail
:>     FAQ needs to be updated to recommend softupdates rather then
:>     disrecommend it.
:>
:> 						-Matt
:
:The question still reamins about link/unlink/rename.  Is a fsync of the
:directory necessary to ensure that they completed properly?  As they take
:filenames instead of fds, an fsync after the operation seems
:non-intuitive.  The rename manpage seems to imply that the operation is
:synchronous - the other two are ambiguous.
:
:Mike "Silby" Silbersack

    If you rename a file and then fsync() the file's descriptor, you
    will guarentee the directory structure.  Same with link.  If you
    you unlink a file and still have an open descriptor you can fsync()
    the descriptor to guarentee the directory unlink.  It might be a good
    idea to ftruncate() the file to 0-length in addition to unlinking it,
    prior to calling fsync(), to avoid unnecessary data block writes.

    I've never tried fsync()ing a directory descriptor so I don't know
    if that would work or not. 

    No other filesystem makes guarentees for these operations either.
    Not even normal UFS mounts.

						-Matt


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