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Wong" , Benjamin Coddington , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, v9fs@lists.linux.dev, linux-afs@lists.infradead.org, linux-btrfs@vger.kernel.org, ceph-devel@vger.kernel.org, codalist@coda.cs.cmu.edu, ecryptfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, ntfs3@lists.linux.dev, ocfs2-devel@lists.linux.dev, devel@lists.orangefs.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-mtd@lists.infradead.org, linux-mm@kvack.org, linux-unionfs@vger.kernel.org, linux-xfs@vger.kernel.org, bug-gnulib@gnu.org, Jeff Layton Subject: Re: [PATCH v7 12/13] ext4: switch to multigrain timestamps Date: Tue, 19 Sep 2023 16:52:43 +0200 Message-ID: <4511209.uG2h0Jr0uP@nimes> In-Reply-To: <1f29102c09c60661758c5376018eac43f774c462.camel@kernel.org> References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org> <20230919110457.7fnmzo4nqsi43yqq@quack3> <1f29102c09c60661758c5376018eac43f774c462.camel@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230919_075332_654785_FCBFBB9C X-CRM114-Status: GOOD ( 13.98 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org Jeff Layton wrote: > I'm not sure what we can do for this test. The nap() function is making > an assumption that the timestamp granularity will be constant, and that > isn't necessarily the case now. This is only of secondary importance, because the scenario by Jan Kara shows a much more fundamental breakage: > > The ultimate problem is that a sequence like: > > > > write(f1) > > stat(f2) > > write(f2) > > stat(f2) > > write(f1) > > stat(f1) > > > > can result in f1 timestamp to be (slightly) lower than the final f2 > > timestamp because the second write to f1 didn't bother updating the > > timestamp. That can indeed be a bit confusing to programs if they compare > > timestamps between two files. Jeff? > > > > Basically yes. f1 was last written to *after* f2 was last written to. If the timestamp of f1 is then lower than the timestamp of f2, timestamps are fundamentally broken. Many things in user-space depend on timestamps, such as build system centered around 'make', but also 'find ... -newer ...'. Bruno ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/