Date: Fri, 14 Jun 2013 19:01:11 +0000 From: "Teske, Devin" <Devin.Teske@fisglobal.com> To: Kirk McKusick <mckusick@mckusick.com> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>, Devin Teske <dteske@freebsd.org> Subject: Re: ZFS Union Message-ID: <13CA24D6AB415D428143D44749F57D7201F81A60@ltcfiswmsgmb21> In-Reply-To: <201306141851.r5EIpkl2054401@chez.mckusick.com> References: <201306141851.r5EIpkl2054401@chez.mckusick.com>
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On Jun 14, 2013, at 11:51 AM, Kirk McKusick wrote: The union filesystem uses "whiteout" to remove files that appear in a lower layer. In your example, when you `rm /vm/unit1/foo' what happens is that a whiteout entry gets created for /vm/unit1/foo. (Whiteout is implemented by creating a name with inode number 1; Inode 1 is the "anti-inode" which when combined with any other inode disappears in a cloud of greasy smoke.) WINO=85 yes=85 just as your response came in, I was finding the code=85 http://svnweb.freebsd.org/base/head/sys/ufs/ufs/ufs_lookup.c?r1=3D156418&r2= =3D160269 if (ep->d_ino =3D=3D 0 || - (ep->d_ino =3D=3D WINO && + (ep->d_ino =3D=3D WINO && namlen =3D=3D dirp->d_namlen && bcmp(ep->d_name, dirp->d_name, dirp->d_namlen) =3D=3D 0)) { Thus /vm/master/foo continues to exist and is visible as /vm/unit2/foo and /vm/unit3/foo. You can "recover" /vm/unit1/foo using `rm -W /vm/unit1/foo' which will remove the whiteout entry causing /vm/master/foo to once again be visible as /vm/unit1/foo. Beautiful=85 that was my next consternation after seeing that it was in the= filesystem layer (how to reset the value from WINO to something that will = allow the lower layer to bleed through). In short, I believe that the existing union filesystem will do what you want to do. Kirk McKusick Absolutely right=85 thank you much Sir! I didn't know about "rm -W" until today. -- Devin _____________ The information contained in this message is proprietary and/or confidentia= l. If you are not the intended recipient, please: (i) delete the message an= d all copies; (ii) do not disclose, distribute or use the message in any ma= nner; and (iii) notify the sender immediately. In addition, please be aware= that any message addressed to our domain is subject to archiving and revie= w by persons other than the intended recipient. Thank you.
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