Date: Tue, 06 Feb 2001 09:07:58 -0800 From: Julian Elischer <julian@elischer.org> To: Mike Silbersack <silby@silby.com> Cc: Rik van Riel <riel@conectiva.com.br>, 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, mckusick@mckusick.com Subject: Re: soft updates and qmail (RE: qmail IO problems) Message-ID: <3A802F6E.D4582D54@elischer.org> References: <Pine.BSF.4.31.0102061149180.14899-100000@achilles.silby.com>
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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 ... > > > > regards, > > > > Rik > > Well, the various qmail programs do seem to fsync (though I'm not sure if > it's in the right places.) In any case, this link seems to throw some > light on the situation: > > ftp://elektroni.ee.tut.fi/pub/qmail_linux_metadata_message > > Now, I have no clue if this is correct or not, but the core of the > explanation given on that page seems to be: > > --- > > 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. 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. > > --- > > So, does anyone know if that is a correct assertion to make, and if > softupdates does indeed break it? kirk said (but I have not completely checked it) that if you fsync a file, it will effectively fsync all the way back to the root of the filesystem. I don't know how true this is, but cerainly the inode is updated before fsync returns. I cannot tell if any directory entries pointing at that file that have not yet been sync'd are forced out before it returns.... > > Mike "Silby" Silbersack > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message -- __--_|\ Julian Elischer / \ julian@elischer.org ( OZ ) World tour 2000-2001 ---> X_.---._/ v To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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