From owner-freebsd-questions Thu Sep 5 7:46:33 2002 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 61D3837B400 for ; Thu, 5 Sep 2002 07:46:29 -0700 (PDT) Received: from mail.thundernet.cz (mail.thundernet.cz [62.77.87.114]) by mx1.FreeBSD.org (Postfix) with SMTP id BDDA043E4A for ; Thu, 5 Sep 2002 07:46:27 -0700 (PDT) (envelope-from neuhauser@bellavista.cz) Received: (qmail 5768 invoked from network); 5 Sep 2002 14:46:25 -0000 Received: from unknown (HELO freepuppy.bellavista.cz) (62.168.44.50) by mail.thundernet.cz with SMTP; 5 Sep 2002 14:46:25 -0000 Received: by freepuppy.bellavista.cz (Postfix, from userid 1001) id 4B8D6141; Thu, 5 Sep 2002 16:46:28 +0200 (CEST) Date: Thu, 5 Sep 2002 16:46:28 +0200 From: Roman Neuhauser To: Lowell Gilbert Cc: freebsd-questions@freebsd.org Subject: Re: mount(8) mount_union(8) and the slippery wet floor... Message-ID: <20020905144627.GL10717@freepuppy.bellavista.cz> Mail-Followup-To: Lowell Gilbert , freebsd-questions@freebsd.org References: <5.1.0.14.0.20020904132723.00bc28e8@mail.lusidor.nu> <20020904124832.GA15994@submonkey.net> <44y9ahecn2.fsf@be-well.ilk.org> <20020905091754.GE10717@freepuppy.bellavista.cz> <44bs7c1phq.fsf@be-well.ilk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <44bs7c1phq.fsf@be-well.ilk.org> User-Agent: Mutt/1.5.1i Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG # freebsd-questions-local@be-well.no-ip.com / 2002-09-05 10:26:57 -0400: > Roman Neuhauser writes: > > # freebsd-questions-local@be-well.no-ip.com / 2002-09-04 16:13:53 -0400: > > > Ceri Davies writes: > > > > > > > On Wed, Sep 04, 2002 at 01:46:42PM +0200, Jimmy Lantz wrote: > > > > > Hi, > > > > > > > > > > My question is: > > > > > Is the mount union mentioned in MOUNT(8) also affected by the > > > > > slippery wet floor in MOUNT_UNION(8)?? > > > > > Or can I safely use the mount with the option union? > > > > > > > > They are the same thing. > > > > > > For the record, they are *not* the same thing. > > > > could you elaborate? > > I'm not 100% sure that I completely understand the technical details, > but I'll give it a shot. You could go check the archives of the > freebsd-fs list for more authoritative information on the subject. > > Very briefly, they implement similar functionality through different > abstractions. mount_union is a filesystem in its own right -- it > "stacks" on top of other filesystem types and uses their capabilities > to perform the I/O operations, but to the system I/O code, it looks > like a filesystem. The union mount option is visible at a higher > level; the filesystem code itself doesn't know about the shadowing. > > Or something like that. At any rate, they don't seem to share any > code. this is interesting. I always thought that mount(8) works by invoking mount_whatever(8) where whatever is determined by the value passed in the -t option to mount(8). looks like this isn't the case, then... hm: If the type is not one of the internally known types, mount will attempt to execute a program in /sbin/mount_XXX where XXX is replaced by the type name. For example, nfs filesystems are mounted by the program /sbin/mount_nfs. And elsewhere: For example, the mount command: mount -t mfs -o nosuid,-N,-s=4000 /dev/dk0b /tmp causes mount to execute the equivalent of: /sbin/mount_mfs -o nosuid -N -s 4000 /dev/dk0b /tmp So, this would look as though mount -t union / mount_union is a hack defiating from the normal way these commands operate? -- begin 666 nonexistent.vbs FreeBSD 4.6-STABLE 4:33PM up 15 days, 22:26, 8 users, load averages: 0.10, 0.04, 0.01 end To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message