From owner-freebsd-fs Wed May 1 23:48:53 2002 Delivered-To: freebsd-fs@freebsd.org Received: from swan.prod.itd.earthlink.net (swan.mail.pas.earthlink.net [207.217.120.123]) by hub.freebsd.org (Postfix) with ESMTP id 3116D37B417 for ; Wed, 1 May 2002 23:48:50 -0700 (PDT) Received: from pool0052.cvx21-bradley.dialup.earthlink.net ([209.179.192.52] helo=mindspring.com) by swan.prod.itd.earthlink.net with esmtp (Exim 3.33 #2) id 173AOL-0001G0-00; Wed, 01 May 2002 23:48:38 -0700 Message-ID: <3CD0E128.980AA927@mindspring.com> Date: Wed, 01 May 2002 23:48:08 -0700 From: Terry Lambert X-Mailer: Mozilla 4.7 [en]C-CCK-MCD {Sony} (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: kudzu@tenebras.com Cc: Ian Dowse , utsl@quic.net, "Andrew P. Lentvorski" , freebsd-fs@freebsd.org Subject: Re: Non-standard root filesystems References: <200205012115.aa68752@salmon.maths.tcd.ie> <3CD04F45.1040704@tenebras.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org Michael Sierchio wrote: > Ian Dowse wrote: > > I never said anything about using union filesystems; you can just > > mount another filesystem directly over /, and it hides the underlying > > root filesystem. > > Covering mounts are also broken, IIRC, with the same cache coherency > problem. I may be mistaken, but the problem is with NULLFS, which > is required for covering mounts. He's talking a fully covering mount, not a stacking mount. The coherency issues are particular to the stacking process, and to the "unionfs", which is a stacking FS. The "union" mount option, which is handled internally to the FS framework itself, has different problems. The main problem with covering mounts is what happens to inferior mount points, when you cover a mount point higher up in the mount hierarchy (e.g. "What happens to an already mounted "/usr/" when you cover over "/"?"), and "slip under" (e.g. "How do I replace, rather than cover, an FS at a mount point?"). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message