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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3E189E728C2 for ; Fri, 29 Sep 2023 15:36:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=0/8ulbJKNu2T4SBrsBeBbdbR1+IVBJiwNhPmGn8rXHA=; b=gHuA6qYVausY7t whJxPfDTKx5tiptBiKtPL6C+QD4NweyYJ7wrb7j9/6oo/Lr6UJOJC9lGvC1c7ielZa5u2QeqQ5RVa 4UbrgPTuD7SXahYnVz8yjVuCXG54EJZ83y8Bl4EE3+7NUxFG9gwKa8jbxakrezEh2nhkllponb1Ie dWIxYu96bQk4FNeZBZjpqA1s1LR9HbscuC0LEPXa/T1BOHwjmdbuzh/sV+Ieksxtn4bo+LUpD+uYn avvVp5q2qMtsUZ1/E9bd/mAgMjAoKX+juqYqfAG20Mt0Y45Kf4Z1iTu9O46upADxJbNrBJCh+oLiC Jc2rfL+LraonuF6clF/w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qmFXi-008CZy-2p; Fri, 29 Sep 2023 15:36:38 +0000 Received: from outgoing-auth-1.mit.edu ([18.9.28.11] helo=outgoing.mit.edu) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qlyap-006iVR-1P for linux-um@lists.infradead.org; Thu, 28 Sep 2023 21:30:45 +0000 Received: from cwcc.thunk.org (pool-173-48-111-87.bstnma.fios.verizon.net [173.48.111.87]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 38SLQvsA021537 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 28 Sep 2023 17:26:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mit.edu; s=outgoing; t=1695936425; bh=w4hql40FuyyfsTNK9D530X9ExV2y5b7TU7/1a0HHsnU=; h=Date:From:Subject:Message-ID:MIME-Version:Content-Type; b=NGPOVv6aP7Wgx4/k9ruqGjDYWmjUQVAfEL5fppG6yE2RNxUM6uiyoWrXBZfGmZyL2 gb1zEZjWcSSCFd+NWg1/BYhZ5jeEptXNin1ZAM6seg38Angccj8YOPtyzxOx/hDFrb Q+ePr/t98/fHq2BcSzJCThnFTNb50fVmlIrGfb3oMvB11ToZpH+p8R2mhaDk4/44dl uEHGVh6Q6Ih5iyFuN8+PasXijpXT1PXJm+5Rkla8PX5Glna1OAsFe3wre6CQl62oa4 RAr1Z2b44rKF067M11yaRPI56z2wMDur4vLyEnjrhgmaYzW5D9XQ8I+PJlbP887wDq NXSNNWLPWiTbQ== Received: by cwcc.thunk.org (Postfix, from userid 15806) id 06AD715C0266; Thu, 28 Sep 2023 17:26:57 -0400 (EDT) Date: Thu, 28 Sep 2023 17:26:56 -0400 From: "Theodore Ts'o" To: Jeff Layton Cc: "Darrick J. Wong" , Arnd Bergmann , Alexander Viro , Christian Brauner , Linus Torvalds , David Sterba , Amir Goldstein , "Eric W. Biederman" , Kees Cook , Jeremy Kerr , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Greg Kroah-Hartman , Arve =?iso-8859-1?B?SGr4bm5lduVn?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Mattia Dongili , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Brad Warrum , Ritu Agarwal , Hans de Goede , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Mark Gross , Jiri Slaby , Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck , David Sterba , David Howells , Marc Dionne , Ian Kent , Luis de Bethencourt , Salah Triki , "Tigran A. Aivazian" , Chris Mason , Josef Bacik , Xiubo Li , Ilya Dryomov , Jan Harkes , coda@cs.cmu.edu, Joel Becker , Christoph Hellwig , Nicolas Pitre , "Rafael J . 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Hallyn" , Stephen Smalley , Eric Paris , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-rdma@vger.kernel.org, linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, v9fs@lists.linux.dev, linux-afs@lists.infradead.org, autofs@vger.kernel.org, linux-btrfs@vger.kernel.org, ceph-devel@vger.kernel.org, codalist@telemann.coda.cs.cmu.edu, linux-efi@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, gfs2@lists.linux.dev, linux-um@lists.infradead.org, linux-mtd@lists.infradead.org, jfs-discussion@lists.sourceforge.net, linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, ntfs3@lists.linux.dev, ocfs2-devel@lists.linux.dev, linux-karma-devel@lists.sourceforge.net, devel@lists.orangefs.org, linux-unionfs@vger.kernel.org, linux-hardening@vger.kernel.org, reiserfs-devel@vger.kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, linux-trace-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, bpf@vger.kernel.org, Netdev , apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, selinux@vger.kernel.org Subject: Re: [PATCH 86/87] fs: switch timespec64 fields in inode to discrete integers Message-ID: <20230928212656.GC189345@mit.edu> References: <20230928110554.34758-1-jlayton@kernel.org> <20230928110554.34758-2-jlayton@kernel.org> <6020d6e7-b187-4abb-bf38-dc09d8bd0f6d@app.fastmail.com> <20230928171943.GK11439@frogsfrogsfrogs> <6a6f37d16b55a3003af3f3dbb7778a367f68cd8d.camel@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <6a6f37d16b55a3003af3f3dbb7778a367f68cd8d.camel@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230928_143043_631718_3530938E X-CRM114-Status: GOOD ( 22.98 ) X-Mailman-Approved-At: Fri, 29 Sep 2023 08:36:32 -0700 X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Thu, Sep 28, 2023 at 01:40:55PM -0400, Jeff Layton wrote: > > Correct. We'd lose some fidelity in currently stored timestamps, but as > Linus and Ted pointed out, anything below ~100ns granularity is > effectively just noise, as that's the floor overhead for calling into > the kernel. It's hard to argue that any application needs that sort of > timestamp resolution, at least with contemporary hardware. > > Doing that would mean that tests that store specific values in the > atime/mtime and expect to be able to fetch exactly that value back would > break though, so we'd have to be OK with that if we want to try it. The > good news is that it's relatively easy to experiment with new ways to > store timestamps with these wrappers in place. The reason why we store 1ns granularity in ext4's on-disk format (and accept that we only support times only a couple of centuries into the future, as opposed shooting for an on-disk format good for several millennia :-), was in case there was userspace that might try to store a very fine-grained timestamp and want to be able to get it back bit-for-bit identical. For example, what if someone was trying to implement some kind of steganographic scheme where they going store a secret message (or more likely, a 256-bit AES key) in the nanosecond fields of the file's {c,m,a,cr}time timestamps, "hiding in plain sight". Not that I think that we have to support something like that, since the field is for *timestamps* not cryptographic bits, so if we break someone who is doing that, do we care? I don't think anyone will complain about breaking the userspace API --- especially since if, say, the CIA was using this for their spies' drop boxes, they probably wouldn't want to admit it. :-) - Ted _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um