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From: guy@gorodish.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: O_SYNC and filesystem updating
Message-ID: <13321@sun.uucp>
Date: Sat, 14-Feb-87 17:15:04 EST
Article-I.D.: sun.13321
Posted: Sat Feb 14 17:15:04 1987
Date-Received: Sun, 15-Feb-87 07:38:41 EST
References: <11470@gatech.EDU> <12946@sun.uucp> <413@yabbie.rmit.oz>
Sender: news@sun.uucp
Reply-To: guy@sun.UUCP (Guy Harris)
Organization: Sun Microsystems, Mountain View
Lines: 10
Keywords: O_SYNC, System V, reliability? What reliability?
Summary: O_SYNC is controllable with "fcntl" as well as "open"

>It is not sensible to ensure that *every* write be syncronously updated
>to disk.

The O_SYNC flag is controllable by "fcntl".  You can turn it on when
opening the file (or not - I hope that writes done when *creating* a
file are done so that there won't be any serious file system
inconsistencies *regardless* of whether O_SYNC is set), turn it off
for most writes, and turn it back on when you are about to do a write
that must be flushed to disk at that time.  There's no need to open
two file descriptors.