From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 20D11C352A4 for ; Wed, 12 Feb 2020 19:58:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 013D721739 for ; Wed, 12 Feb 2020 19:58:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727548AbgBLT6I (ORCPT ); Wed, 12 Feb 2020 14:58:08 -0500 Received: from 216-12-86-13.cv.mvl.ntelos.net ([216.12.86.13]:50532 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727361AbgBLT6I (ORCPT ); Wed, 12 Feb 2020 14:58:08 -0500 Received: from dalias by brightrain.aerifal.cx with local (Exim 3.15 #2) id 1j1y6p-0004qS-00; Wed, 12 Feb 2020 19:55:43 +0000 Date: Wed, 12 Feb 2020 14:55:43 -0500 From: Rich Felker To: Al Viro Cc: Florian Weimer , "Darrick J. Wong" , Christoph Hellwig , linux-xfs@vger.kernel.org, libc-alpha@sourceware.org, linux-fsdevel@vger.kernel.org Subject: Re: XFS reports lchmod failure, but changes file system contents Message-ID: <20200212195543.GA1663@brightrain.aerifal.cx> References: <874kvwowke.fsf@mid.deneb.enyo.de> <20200212161604.GP6870@magnolia> <20200212181128.GA31394@infradead.org> <20200212183718.GQ6870@magnolia> <87d0ajmxc3.fsf@mid.deneb.enyo.de> <20200212195118.GN23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200212195118.GN23230@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Feb 12, 2020 at 07:51:18PM +0000, Al Viro wrote: > On Wed, Feb 12, 2020 at 08:15:08PM +0100, Florian Weimer wrote: > > > | Further, I've found some inconsistent behavior with ext4: chmod on the > > | magic symlink fails with EOPNOTSUPP as in Florian's test, but fchmod > > | on the O_PATH fd succeeds and changes the symlink mode. This is with > > | 5.4. Cany anyone else confirm this? Is it a problem? > > > > It looks broken to me because fchmod (as an inode-changing operation) > > is not supposed to work on O_PATH descriptors. > > Why? O_PATH does have an associated inode just fine; where does > that "not supposed to" come from? Indeed, my expectation was that both fchmod and chmod via the magic symlink succeed, given a new enough kernel for operations on O_PATH fds to be supported. I'd like to switch to using fstat+fchmod to do this, and only fallback to /proc on older kernels where O_PATH fds cause EBADF. But I'm somewhat concerned by the inconsistency between behavior of the two approaches. Rich