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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 3E27BC2D0EF for ; Fri, 17 Apr 2020 17:19:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A9042078E for ; Fri, 17 Apr 2020 17:19:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728712AbgDQRTi (ORCPT ); Fri, 17 Apr 2020 13:19:38 -0400 Received: from mga12.intel.com ([192.55.52.136]:38364 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728162AbgDQRTh (ORCPT ); Fri, 17 Apr 2020 13:19:37 -0400 IronPort-SDR: aEyryLCkhgfAPbbLSBdFjw6ieQacCmrTcjjGIE+toJ7E4OuZzeL1F+7hB6d78l7yuyZTA34FAn 2kQHnsVR4uvA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Apr 2020 10:19:36 -0700 IronPort-SDR: PLkem773MNJbcn2ONOYkpbZvrY7xDpNrF167sHCQ6p1V8QhAE99GtvdakzYl9hbOr8WqAiOY9d 8jS1H0TzeeTw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,395,1580803200"; d="scan'208";a="428292211" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga005.jf.intel.com with ESMTP; 17 Apr 2020 10:19:36 -0700 Date: Fri, 17 Apr 2020 10:19:36 -0700 From: Ira Weiny To: Andreas Dilger Cc: "Darrick J. Wong" , linux-kernel@vger.kernel.org, Jan Kara , Dan Williams , Dave Chinner , Christoph Hellwig , "Theodore Y. Ts'o" , Jeff Moyer , linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag Message-ID: <20200417171936.GT2309605@iweiny-DESK2.sc.intel.com> References: <20200417022036.GQ2309605@iweiny-DESK2.sc.intel.com> <324CEF76-20AA-40F5-A31B-6E0B1CCED736@dilger.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <324CEF76-20AA-40F5-A31B-6E0B1CCED736@dilger.ca> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 17, 2020 at 12:43:39AM -0600, Andreas Dilger wrote: > We still need to store an on-disk DAX flag for Ext4, and at that point it > doesn't make sense not to expose it via the standard Ext4 chattr utility. > > So having EXT4_DAX_FL (== FS_DAX_FL) is no extra effort to add. I'll leave it exposed then. Thanks, Ira > > Cheers, Andreas > > > On Apr 16, 2020, at 20:20, Ira Weiny wrote: > > > > On Thu, Apr 16, 2020 at 06:57:31PM -0700, Darrick J. Wong wrote: > >>> On Thu, Apr 16, 2020 at 05:37:19PM -0700, Ira Weiny wrote: > >>> On Thu, Apr 16, 2020 at 03:49:37PM -0700, Darrick J. Wong wrote: > >>>> On Thu, Apr 16, 2020 at 03:33:27PM -0700, Ira Weiny wrote: > >>>>> On Thu, Apr 16, 2020 at 09:25:04AM -0700, Darrick J. Wong wrote: > >>>>>> On Mon, Apr 13, 2020 at 09:00:26PM -0700, ira.weiny@intel.com wrote: > >>>>>>> From: Ira Weiny > >>>>>>> > >>>>>>> Add a flag to preserve FS_XFLAG_DAX in the ext4 inode. > >>>>>>> > >>>>>>> Set the flag to be user visible and changeable. Set the flag to be > >>>>>>> inherited. Allow applications to change the flag at any time. > >>>>>>> > >>>>>>> Finally, on regular files, flag the inode to not be cached to facilitate > >>>>>>> changing S_DAX on the next creation of the inode. > >>>>>>> > >>>>>>> Signed-off-by: Ira Weiny > >>>>>>> --- > >>>>>>> fs/ext4/ext4.h | 13 +++++++++---- > >>>>>>> fs/ext4/ioctl.c | 21 ++++++++++++++++++++- > >>>>>>> 2 files changed, 29 insertions(+), 5 deletions(-) > >>>>>>> > >>>>>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > >>>>>>> index 61b37a052052..434021fcec88 100644 > >>>>>>> --- a/fs/ext4/ext4.h > >>>>>>> +++ b/fs/ext4/ext4.h > >>>>>>> @@ -415,13 +415,16 @@ struct flex_groups { > >>>>>>> #define EXT4_VERITY_FL 0x00100000 /* Verity protected inode */ > >>>>>>> #define EXT4_EA_INODE_FL 0x00200000 /* Inode used for large EA */ > >>>>>>> #define EXT4_EOFBLOCKS_FL 0x00400000 /* Blocks allocated beyond EOF */ > >>>>>>> + > >>>>>>> +#define EXT4_DAX_FL 0x00800000 /* Inode is DAX */ > >>>>>> > >>>>>> Sooo, fun fact about ext4 vs. the world-- > >>>>>> > >>>>>> The GETFLAGS/SETFLAGS ioctl, since it came from ext2, shares the same > >>>>>> flag values as the ondisk inode flags in ext*. Therefore, each of these > >>>>>> EXT4_[whatever]_FL values are supposed to have a FS_[whatever]_FL > >>>>>> equivalent in include/uapi/linux/fs.h. > >>>>> > >>>>> Interesting... > >>>>> > >>>>>> > >>>>>> (Note that the "[whatever]" is a straight translation since the same > >>>>>> uapi header also defines the FS_XFLAG_[xfswhatever] flag values; ignore > >>>>>> those.) > >>>>>> > >>>>>> Evidently, FS_NOCOW_FL already took 0x800000, but ext4.h was never > >>>>>> updated to note that the value was taken. I think Ted might be inclined > >>>>>> to reserve the ondisk inode bit just in case ext4 ever does support copy > >>>>>> on write, though that's his call. :) > >>>>> > >>>>> Seems like I should change this... And I did not realize I was inherently > >>>>> changing a bit definition which was exposed to other FS's... > >>>> > >>>> This whole thing is a mess, particularly now that we have two vfs > >>>> ioctls to set per-fs inode attributes, both of which were inherited from > >>>> other filesystems... :( > >>>> > >>> > >>> Ok I've changed it. > >>> > >>>> > >>>>>> > >>>>>> Long story short - can you use 0x1000000 for this instead, and add the > >>>>>> corresponding value to the uapi fs.h? I guess that also means that we > >>>>>> can change FS_XFLAG_DAX (in the form of FS_DAX_FL in FSSETFLAGS) after > >>>>>> that. > >>>>> > >>>>> :-/ > >>>>> > >>>>> Are there any potential users of FS_XFLAG_DAX now? > >>>> > >>>> Yes, it's in the userspace ABI so we can't get rid of it. > >>>> > >>>> (FWIW there are several flags that exist in both FS_XFLAG_* and FS_*_FL > >>>> form.) > >>>> > >>>>> From what it looks like, changing FS_XFLAG_DAX to FS_DAX_FL would be pretty > >>>>> straight forward. Just to be sure, looks like XFS converts the FS_[xxx]_FL to > >>>>> FS_XFLAGS_[xxx] in xfs_merge_ioc_xflags()? But it does not look like all the > >>>>> FS_[xxx]_FL flags are converted. Is is that XFS does not support those > >>>>> options? Or is it depending on the VFS layer for some of them? > >>>> > >>>> XFS doesn't support most of the FS_*_FL flags. > >>> > >>> If FS_XFLAG_DAX needs to continue to be user visible I think we need to keep > >>> that flag and we should not expose the EXT4_DAX_FL flag... > >>> > >>> I think that works for XFS. > >>> > >>> But for ext4 it looks like EXT4_FL_XFLAG_VISIBLE was intended to be used for > >>> [GET|SET]XATTR where EXT4_FL_USER_VISIBLE was intended to for [GET|SET]FLAGS... > >>> But if I don't add EXT4_DAX_FL in EXT4_FL_XFLAG_VISIBLE my test fails. > >>> > >>> I've been playing with the flags and looking at the code and I _thought_ the > >>> following patch would ensure that FS_XFLAG_DAX is the only one visible but for > >>> some reason FS_XFLAG_DAX can't be set with this patch. I still need the > >>> EXT4_FL_USER_VISIBLE mask altered... Which I believe would expose EXT4_DAX_FL > >>> directly as well. > >>> > >>> Jan, Ted? Any ideas? Or should we expose EXT4_DAX_FL and FS_XFLAG_DAX in > >>> ext4? > >> > >> Both flags should be exposed through their respective ioctl interfaces > >> in both filesystems. That way we don't have to add even more verbiage > >> to the documentation to instruct userspace programmers on how to special > >> case ext4 and XFS for the same piece of functionality. > > > > Wouldn't it be more confusing for the user to have 2 different flags which do > > the same thing? > > > > I would think that using FS_XFLAG_DAX _only_ (for both ext4 and xfs) would be > > easier without special cases? > > > > Ira > >