From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752261AbdGGQrD (ORCPT ); Fri, 7 Jul 2017 12:47:03 -0400 Received: from fieldses.org ([173.255.197.46]:52512 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750726AbdGGQrB (ORCPT ); Fri, 7 Jul 2017 12:47:01 -0400 Date: Fri, 7 Jul 2017 12:47:00 -0400 From: "J. Bruce Fields" To: Jeff Layton Cc: "Theodore Ts'o" , "Darrick J. Wong" , William Koh , Andreas Dilger , linux-ext4 , lkml , Kernel Team , linux-fsdevel , Trond Myklebust , xfs Subject: Re: [PATCH] fs: ext4: inode->i_generation not assigned 0. Message-ID: <20170707164700.GA18740@fieldses.org> References: <20170629172528.GA5869@birch.djwong.org> <20170629183053.GA4178@fieldses.org> <20170629185022.GB4178@fieldses.org> <20170704040446.GB4704@birch.djwong.org> <20170705011534.GC1420@fieldses.org> <20170705191933.GA6297@magnolia> <20170705202750.j5texbm2xdxnph6m@thunk.org> <1499424697.5826.3.camel@redhat.com> <20170707155117.4zp7qkpreeptwlgc@thunk.org> <1499444016.4967.1.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1499444016.4967.1.camel@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 07, 2017 at 12:13:36PM -0400, Jeff Layton wrote: > On Fri, 2017-07-07 at 11:51 -0400, Theodore Ts'o wrote: > > On Fri, Jul 07, 2017 at 06:51:37AM -0400, Jeff Layton wrote: > > > > > > Right. That's the case today if we don't remove support for old > > > filehandles. If we were to remove them, the clients would get back > > > -ESTALE there if they tried to use the old 2.2-style fh's that they saw > > > before the upgrade. > > > > > > The main takeaway here is that NFS filehandle lifetime is really only > > > bounded by the boot time of the oldest clients. > > > > Well, and how long an NFS server is still up. So one could construct > > a use case where a (hypothetical) system administrator had a RHEL 7.0 > > system with a 2.2.16-22 kernel, and they try to update it to a > > (hypothetical) RHEL 10 kernel in one fell swoop with a 4.13+ kernel > > that no longer supports the 2-2-style fh's. A client that had the > > server mounted when it was running the 2.2 kernel might only be up for > > a few hours, before the upgrade to RHEL 10 happened, and then the > > client would get ESTALE errors. > > > > Of course, I've stopped carrying about enterprise kernel support a > > long time ago, so I just think that scenario is funny. I recognize > > that folks who work at Red Hat have to worry about such things --- and > > I'm sorry. :-) > > > > In reality a server installed with RHEL 7.0 has probably died of old > > age by now --- unless someone crazy is running it in a VMware VM > > because they had some enterprise software package or some bar-code > > printing module for which they don't have source code[1], and so they are > > stuck on RHEL 7.0, even in 2017. Have I mentioned I'm so glad I don't > > have to worry these sorts of things any more? RHEL 7 is current, I think you mean the 17-year-old Red Hat Linux 7. Anyone that far back is on their own as far as any enterprise distro is concerned. There are some exceptions to the "lifetime of a mount" rule, none real issues, I think: - fscache may keep fh's around across client boots, but I suspect you just lose the benefit of the cache until it expires data keyed under old filehandles and repopulates the cache with new ones. - Does the client actually depend on stable filehandles across client reboots if it might cache write data under a persistent delegation? But seeing as we don't even implement persistent delegations, this is a non-issue. - nontraditional NFS clients could do any random thing. NFS is just a protocol, we have no idea how some weird application that talks NFS directly to the server might use filehandles. But this is purely hypothetical, I don't know of one. --b.