From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH v3] ovl: Check link ability between upperdir and workdir Date: Tue, 19 Dec 2017 08:48:49 -0500 Message-ID: <20171219134849.GA2737@redhat.com> References: <1513601748-57439-1-git-send-email-cgxu519@icloud.com> <20171218160251.GA7474@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51750 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763009AbdLSNsu (ORCPT ); Tue, 19 Dec 2017 08:48:50 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-unionfs-owner@vger.kernel.org List-Id: linux-unionfs@vger.kernel.org To: Chengguang Xu Cc: Miklos Szeredi , amir73il@gmail.com, linux-unionfs@vger.kernel.org On Tue, Dec 19, 2017 at 09:49:28AM +0800, Chengguang Xu wrote: > > > > 在 2017年12月19日，上午12:02，Vivek Goyal 写道： > > > > On Mon, Dec 18, 2017 at 08:55:48PM +0800, Chengguang Xu wrote: > >> Inspired by encountering unexpected write error when > >> upperdir and workdir having different project ids. > > > > Can you please make this problem descrition little better. By > > these two lines I really don't understand what's the problem > > you are trying to solve. All I understood was that upperdir > > and workdir had different project id. But not sure what > > problem it led to and why. > > > > In fact your first patch changelong was little better. It > > atleast said that you encounter "-EXDEV". So is it rename > > which fails. So rename is not allowed between two directories > > having different project ids? > > > > The background is > I encountered an unexpected write error with error code -EXDEV in > my environment which didn’t break any rules in overlayfs kernel > document. > > So I did some investigations and found when upperdir and workdir > having different project quotas then rename/link operations between > those directories would be fail with -EXDEV because project quota > asks files in it strictly inherit project id with it’s own. This will > make write fail during copy-up process. > > I wrote first patch to check this condition, but that check seems not > sufficient to detect write error, so after discussion with Amir, > we decided to check link ability between upperdir and workdir, it is > what copy-up actually doing when modifying files in lowerdirs, and also > I decided to only print a warning message instead of directly mounting > on read-only mode in case there is a special use case just read and do not > modify anything in lowerdirs. Ok, thanks for the explanation. I really wish that some of it makes to changelog so that somebody reading it later finds it much easier to understand. BTW, just curious, when upper supports O_TMPFILE, do we have to create tmpfile in workdir/. Can we create it in upper/ and then link in appropriate destination directory. Amir, is there a fundamental requirement about why tmpfile creation has to be in workdir. Vivek