From owner-freebsd-hackers Tue Dec 4 23:26:50 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from snipe.prod.itd.earthlink.net (snipe.mail.pas.earthlink.net [207.217.120.62]) by hub.freebsd.org (Postfix) with ESMTP id 0E6F137B419; Tue, 4 Dec 2001 23:26:44 -0800 (PST) Received: from dialup-209.244.107.135.dial1.sanjose1.level3.net ([209.244.107.135] helo=blossom.cjclark.org) by snipe.prod.itd.earthlink.net with esmtp (Exim 3.33 #1) id 16BWS2-00046Q-00; Tue, 04 Dec 2001 23:26:43 -0800 Received: (from cjc@localhost) by blossom.cjclark.org (8.11.6/8.11.3) id fB57QdC83515; Tue, 4 Dec 2001 23:26:39 -0800 (PST) (envelope-from cjc) Date: Tue, 4 Dec 2001 23:26:39 -0800 From: "Crist J . Clark" To: Greg Black Cc: Matthew Dillon , Ian Dowse , Bernd Walter , Mark Hannon , bugs-followup@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: bin/32261: dump creates a dump file much larger than sum of dumped files Message-ID: <20011204232639.F40864@blossom.cjclark.org> Reply-To: cjclark@alum.mit.edu References: <200112041339.aa05506@salmon.maths.tcd.ie> <200112041957.fB4Jv1j20226@apollo.backplane.com> <20011204225814.E40864@blossom.cjclark.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from gjb@gbch.net on Wed, Dec 05, 2001 at 05:10:49PM +1000 X-URL: http://people.freebsd.org/~cjc/ Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wed, Dec 05, 2001 at 05:10:49PM +1000, Greg Black wrote: > "Crist J . Clark" wrote: > > | On Wed, Dec 05, 2001 at 06:02:49AM +1000, Greg Black wrote: > | > Matthew Dillon wrote: > | > > | > | :In message <20011204135626.A75212@cicely8.cicely.de>, Bernd Walter writes: > | > | :>> Is there any reason we don't want to truncate the file? Does O_TRUNC > | > | :>> not work well of the file is a tape device or something? > | > | :> > | > | :>I don't expect O_TRUNK to work on devices such tapes and disks. > | > | : > | > | :Well, it won't achieve anything on tapes or disk devices, but it > | > | :should be completely harmless to add the O_TRUNC flag. The current > | > | :behaviour is likely to be unexpected and cause confusion so it > | > | :might as well be changed. I'll commit this later unless someone > | > | :can think of a good reason not to. > | > | : > | > | :Ian > | > | > | > | Woa! That sounds like a bad idea to me. If you want to do it right > | > | then open(), fstat(), and only if the stat says it is a regular file > | > | do you then ftruncate(). Passing O_TRUNC to a tape device may be ignored > | > | by us, but it's not a valid flag to pass to a tape device and we shouldn't > | > | do it. > | > > | > I haven't used any of them for a while, but there are certainly > | > Unix systems that treat O_TRUNC as a signal to rewind a tape > | > device before writing to it. > | > | So? Who cares? This is FreeBSD's dump(8) and FreeBSD's write(2). There > | is no reason to worry about portability of FreeBSD's dump(8) in how > | write(2) flags work. If our write(2) "does the right thing" with > | O_TRUNC and tape devices, there is no reason not to let it do the > | right thing on its own. > > That's a rather strange attitude. All I was suggesting that, > from the once-respected POLA, it would be less surprising to > people who might have experience of other systems if FreeBSD did > not make its own arrangements without some good reason. From what Ian said elsewhere in this thread, the O_TRUNC already does not "act strange" on a tape device. I don't see any new POLA issues if adding O_TRUNC to the write call doesn't change how dump(8) has been working on tapes for FreeBSD for these n years now. The only POLA issue I see is the current behavior that "regular" files are _not_ truncated, which was the start of the thread and the issue in the PR. > There's > no need for responses like: "So? Who cares?" -- if there's some > reason not to consider other people, by all means explain it; > but be polite while you're at it. I don't see who would care if FreeBSD's dump(8) might have some funny reactions on UNIX-like systems where O_TRUNC has a different behavior on tape devices. I don't think the Project is overly concerned about porting FreeBSD's dump(8) to other OSes. -- Crist J. Clark | cjclark@alum.mit.edu | cjclark@jhu.edu http://people.freebsd.org/~cjc/ | cjc@freebsd.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message