From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752252AbdBFVwh (ORCPT ); Mon, 6 Feb 2017 16:52:37 -0500 Received: from fieldses.org ([173.255.197.46]:47544 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752176AbdBFVwe (ORCPT ); Mon, 6 Feb 2017 16:52:34 -0500 Date: Mon, 6 Feb 2017 16:52:33 -0500 To: James Bottomley Cc: "Theodore Ts'o" , "J. R. Okajima" , Djalal Harouni , Chris Mason , Josh Triplett , "Eric W. Biederman" , Andy Lutomirski , Seth Forshee , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Dongsu Park , David Herrmann , Miklos Szeredi , Alban Crequy , Al Viro , "Serge E. Hallyn" , Phil Estes Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount Message-ID: <20170206215233.GC19704@fieldses.org> References: <1486235880.2484.17.camel@HansenPartnership.com> <1486235972.2484.19.camel@HansenPartnership.com> <4608.1486351540@jrobl> <1486363583.2496.63.camel@HansenPartnership.com> <20170206145044.7xlm6l72kystp5zc@thunk.org> <1486394296.2474.49.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1486394296.2474.49.camel@HansenPartnership.com> User-Agent: Mutt/1.5.21 (2010-09-15) From: bfields@fieldses.org (J. Bruce Fields) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 06, 2017 at 07:18:16AM -0800, James Bottomley wrote: > On Mon, 2017-02-06 at 09:50 -0500, Theodore Ts'o wrote: > > On Sun, Feb 05, 2017 at 10:46:23PM -0800, James Bottomley wrote: > > > Yes, I know the problem. However, I believe most current linux > > > filesystems no longer guarantee stable, for the lifetime of the > > > file, inode numbers. The usual docker container root is overlayfs, > > > which, similarly doesn't support stable inode numbers. I see the > > > odd complaint about docker with overlayfs having unstable inode > > > numbers, but none seems to have any serious repercussions. > > > > Um, no. Most current linux file systems *do* guarantee stable inode > > numbers. For one thing, NFS would break horribly if you didn't have > > stable inode numbers. Never mind applications which depend on POSIX > > semantics. And you wouldn't be able to save games in rogue or > > nethack, either. :-) > > I believe that's why we have the superblock export operations to > manufacture unique filehandles in the absence of inode number > stability. Where did you hear that? I'd expect an NFS client to handle non-unique filehandles better than non-unique inode numbers. I believe our client will -EIO on encountering an inode number change (see nfs_check_inode_attributes().) See also https://tools.ietf.org/html/rfc5661#section-10.3.4. --b. > The generic one uses inode numbers, but it doesn't have to. > I thought reiserfs (if we can go back that far) was the first > generally used filesystem that didn't guarantee stable inode numbers, > so we have a lot of historical precedence. > > Thanks to reiserfs, I thought we also iterated to weak stability > guarantees for inode numbers which mean no inconsistencies in > applications that use inode numbers for caching? It's still not POSIX, > but I thought it was good enough for most use cases. > > > Overlayfs may not, currently, but it's considered a bug. > > James >