From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757119Ab3KLVfP (ORCPT ); Tue, 12 Nov 2013 16:35:15 -0500 Received: from mail-pb0-f46.google.com ([209.85.160.46]:45058 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756125Ab3KLVfK (ORCPT ); Tue, 12 Nov 2013 16:35:10 -0500 Content-Type: multipart/signed; boundary="Apple-Mail=_60C7458F-837E-41F8-8B1E-98D66CD277B4"; protocol="application/pgp-signature"; micalg=pgp-sha1 Mime-Version: 1.0 (Mac OS X Mail 7.0 \(1822\)) Subject: Re: [PATCH] ext4: explain encoding of 34-bit a,c,mtime values From: Andreas Dilger In-Reply-To: <20131112003018.GA30281@thunk.org> Date: Tue, 12 Nov 2013 14:35:04 -0700 Cc: David Turner , Mark Harris , Jan Kara , Ext4 Developers List , Linux Kernel Mailing List Message-Id: <6DE0AF86-98E6-4DE9-BB7F-40FB32E1BC26@dilger.ca> References: <1383808590.23882.13.camel@chiang> <20131107160341.GA3850@quack.suse.cz> <1383864864.23882.33.camel@chiang> <20131107231445.GG2054@quack.suse.cz> <1383866807.23882.41.camel@chiang> <1383981551.8994.27.camel@chiang> <1384070214.8994.47.camel@chiang> <20131112003018.GA30281@thunk.org> To: "Theodore Ts'o" X-Mailer: Apple Mail (2.1822) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Apple-Mail=_60C7458F-837E-41F8-8B1E-98D66CD277B4 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 On Nov 11, 2013, at 5:30 PM, Theodore Ts'o wrote: > On Sun, Nov 10, 2013 at 02:56:54AM -0500, David Turner wrote: >> b. Use Andreas's encoding, which is incompatible with pre-1970 files >> written on 64-bit systems. >>=20 >> I don't care about currently-existing post-2038 files, because I = believe >> that nobody has a valid reason to have such files. However, I do >> believe that pre-1970 files are probably important to someone. >>=20 >> Despite this, I prefer option (b), because I think the simplicity is >> valuable, and because I hate to give up date ranges (even ones that I >> think we'll "never" need). Option (b) is not actually lossy, because = we >> could correct pre-1970 files with e2fsck; under Andreas's encoding, >> their dates would be in the far future (and thus cannot be = legitimate). >>=20 >> Would a patch that does (b) be accepted? I would accompany it with a >> patch to e2fsck (which I assume would also go to the ext4 developers >> mailing list?). >=20 > I agree, I think this is the best way to go. I'm going to drop your > earlier patch, and wait for an updated patch from you. It may miss > this merge window, but as Andreas has pointed out, we still have a few > years to get this right. :-) Since this change would immediately break files encoded with pre-1970 = dates on ext4 filesystems, should there be a transition period where both = pre-1970 dates (with extra epoch bits =3D=3D 0x3 in the current encoding) and = post-2378 (with extra epoch bits =3D=3D 0x3 in the new encoding) are decoded as = being pre-1970? That could be conditional until some release in the future = (e.g. >=3D Linux 4.20, at least 5 years away) to give folks a chance to run = the new e2fsck to fix up those files. Are there really any ext4 filesystems that have files with valid dates = so old? I don=92t want to break anyone=92s data, but if this extra complexity is = completely pointless then I=92m also fine with this minor risk of breakage. Cheers, Andreas --Apple-Mail=_60C7458F-837E-41F8-8B1E-98D66CD277B4 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org iD8DBQFSgp8JpIg59Q01vtYRAv/CAKCLdogtXGO6X8HMSdwlbxcK2njIggCcCjsA XOzvl5skYbfVDyE1MkrysD0= =jGZQ -----END PGP SIGNATURE----- --Apple-Mail=_60C7458F-837E-41F8-8B1E-98D66CD277B4--