From owner-freebsd-questions Thu Sep 5 7:27: 2 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 0CFA237B400 for ; Thu, 5 Sep 2002 07:27:00 -0700 (PDT) Received: from be-well.ilk.org (lowellg.ne.client2.attbi.com [24.147.188.198]) by mx1.FreeBSD.org (Postfix) with ESMTP id BB0E243E3B for ; Thu, 5 Sep 2002 07:26:58 -0700 (PDT) (envelope-from freebsd-questions-local@be-well.no-ip.com) Received: from be-well.ilk.org (lowellg.ne.client2.attbi.com [24.147.188.198]) by be-well.ilk.org (8.12.5/8.12.5) with ESMTP id g85EQvLu034611 for ; Thu, 5 Sep 2002 10:26:57 -0400 (EDT) (envelope-from freebsd-questions-local@be-well.no-ip.com) Received: (from lowell@localhost) by be-well.ilk.org (8.12.5/8.12.5/Submit) id g85EQvxb034608; Thu, 5 Sep 2002 10:26:57 -0400 (EDT) X-Authentication-Warning: be-well.ilk.org: lowell set sender to freebsd-questions-local@be-well.ilk.org using -f To: freebsd-questions@freebsd.org Subject: Re: mount(8) mount_union(8) and the slippery wet floor... 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> From: Lowell Gilbert Date: 05 Sep 2002 10:26:57 -0400 In-Reply-To: <20020905091754.GE10717@freepuppy.bellavista.cz> Message-ID: <44bs7c1phq.fsf@be-well.ilk.org> Lines: 32 User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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 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. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message