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 BD4F5C2BA2B for ; Fri, 17 Apr 2020 02:20:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9CD85206B9 for ; Fri, 17 Apr 2020 02:20:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729226AbgDQCUh (ORCPT ); Thu, 16 Apr 2020 22:20:37 -0400 Received: from mga14.intel.com ([192.55.52.115]:15877 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728969AbgDQCUh (ORCPT ); Thu, 16 Apr 2020 22:20:37 -0400 IronPort-SDR: iGGgdohgwt2s3SYEw4Mul+yyqFBBqZbWAE3h7KWkRf/CBfrkUvUzSNQSvWFz+Kkmu9dk/SUKrz Rh2u/O3YkRLw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Apr 2020 19:20:37 -0700 IronPort-SDR: IyH74imscbpapo+hYD5q4u1fkpMnA7qIrUw0FowKZCiutqF2oWJFnF4W1EAqmWt0NH1GoHFj27 kVw7bxmDjV8Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,393,1580803200"; d="scan'208";a="278218385" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by fmsmga004.fm.intel.com with ESMTP; 16 Apr 2020 19:20:36 -0700 Date: Thu, 16 Apr 2020 19:20:36 -0700 From: Ira Weiny To: "Darrick J. Wong" Cc: 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: <20200417022036.GQ2309605@iweiny-DESK2.sc.intel.com> References: <20200414040030.1802884-1-ira.weiny@intel.com> <20200414040030.1802884-5-ira.weiny@intel.com> <20200416162504.GB6733@magnolia> <20200416223327.GO2309605@iweiny-DESK2.sc.intel.com> <20200416224937.GY6749@magnolia> <20200417003719.GP2309605@iweiny-DESK2.sc.intel.com> <20200417015731.GU6742@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200417015731.GU6742@magnolia> 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 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