Date: Tue, 6 Feb 2001 11:20:39 -0800 (PST) From: Matt Dillon <dillon@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) Message-ID: <200102061920.f16JKdN64467@earth.backplane.com> 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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