Date: Tue, 06 Feb 2001 20:27:49 +0100 From: Andre Oppermann <oppermann@monzoon.net> To: Rik van Riel <riel@conectiva.com.br> Cc: Mike Silbersack <silby@silby.com>, Poul-Henning Kamp <phk@critter.freebsd.dk>, Charles Randall <crandall@matchlogic.com>, 'Matt Dillon' <dillon@earth.backplane.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: <3A805035.C71AAD5E@monzoon.net> References: <Pine.LNX.4.21.0102061555550.1535-100000@duckman.distro.conectiva>
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Rik van Riel wrote: > > On Tue, 6 Feb 2001, Mike Silbersack wrote: > > On Tue, 6 Feb 2001, Rik van Riel wrote: > > > > > The system call used to guarantee this is fsync (and friends?); > > > if qmail doesn't use it but makes assumptions that aren't true > > > on any decent OS out there ... > > > > Well, the various qmail programs do seem to fsync (though I'm > > not sure if it's in the right places.) > > > ftp://elektroni.ee.tut.fi/pub/qmail_linux_metadata_message : > > > So what is this all about? qmail relies on the BSD semantics of > ^^^ > > immediate update of directories on the disk when link(), > > unlink(), open() and rename() calls are used. > > Pre-softupdate BSD semantics, apparently. Doesn't sound like > the smartest thing to do when you want a reliable MTA... This description is not entirely right. Qmail depends on ordered-metadata updates (Terry! :-). That means if you issue a link() to the new place and a unlink() in the old place it should guarantee that the link() happens *BEFORE* the unlink(). At least standard FFS/UFS does this. Linux ext2 might do the the unlink() before the link() and a crash in that moment will loose the file completely. It is all about the ordering guarantee. > > But Linux writes them to the disk asynchronously. My library > > loaded before libc changes those calls to do the corresponding > > directory writes too. Then qmail should be reliable against > > power outages also in Linux. > > If djb could be considered to take things like reliability > and the SMTP specification into account, and not just > security, then qmail would have the potential to be a pretty > decent mailer. He did and qmail is one of the best and most reliable mailers on the Internet. > As it is, I can only recommend people to go with something > like postfix, Exim or zmailer ... Have a look at the qmail source and the facts before you spill out such a *bullshit*! -- Andre To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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