Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933723AbcK2Leb (ORCPT ); Tue, 29 Nov 2016 06:34:31 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36227 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933668AbcK2LeE (ORCPT ); Tue, 29 Nov 2016 06:34:04 -0500 MIME-Version: 1.0 In-Reply-To: References: <20161125212934.GB2622@veci.piliscsaba.szeredi.hu> From: Amir Goldstein Date: Tue, 29 Nov 2016 13:34:01 +0200 Message-ID: Subject: Re: [POC/RFC PATCH] overlayfs: constant inode numbers To: Miklos Szeredi Cc: "linux-unionfs@vger.kernel.org" , linux-fsdevel , linux-kernel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2072 Lines: 45 On Tue, Nov 29, 2016 at 12:16 PM, Miklos Szeredi wrote: > On Mon, Nov 28, 2016 at 12:56 PM, Amir Goldstein wrote: > > [...] > > >> Well, not sure if you noticed my redirect_fh (rediect by file handle) work. >> If differs from redirect by path in 2 major ways: >> 1. Like OVL_XATTR_INO, redirect is set on copy up (but only for dirs) >> 2. Lookup is much simpler (and most likely faster) then full path lookup >> >> It would be trivial to set oe->ino of merged dir from lower most entry in >> ovl_lookup(). > > Okay. In fact always using the handle looks like a better option > overall. File handle should be unique for the lifetime of the > filesystem, while inode numbers may be reused. > > Biggest drawback of the file handle based redirects is exactly that: > makes backing up the overlay basically impossible, since file handles > won't work after a backup + restore. But as an optimization, in > addition to path based redirects it would work fine and provide a good > way to get the stable ino. > Not sure that I understand what you are suggesting, but I would be happy to make the needed adjustments to redirect_fh per your request if you clarify what you mean. From what I understand: 1. If redirect_dir=fh (and supported by layers), store lower handle on dir copy up in new xattr OVL_XATTR_FH 2. In ovl_rename(), set OVL_XATTR_REDIRECT regardless of OVL_XATTR_FH 3. In ovl_lookup_single(), carry both d.redirct and d.redirect_fh to next layer 4. In ovl_lookup_layer(), lookup by handle first then by path Mind you that unlike OVL_XATTR_INO, OVL_XATTR_FH points to *next* inode rather then *lowest* inode, so it does not really improve anything wrt getting the stable inode. Stable inode of merged dir is available after lookup in oe->lowerstack[oe->numlower - 1].dentry->d_inode->i_ino regardless of whether lookup was by handle or by path or no redirect at all, so not sure what you meant by "... and provide a good way to get the stable ino." Either I managed to confuse you, or I am missing something? Amir.