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=-15.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 6B5FFC432BE for ; Fri, 27 Aug 2021 16:23:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40C7660F92 for ; Fri, 27 Aug 2021 16:23:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229552AbhH0QYN (ORCPT ); Fri, 27 Aug 2021 12:24:13 -0400 Received: from sandeen.net ([63.231.237.45]:43204 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234869AbhH0QYN (ORCPT ); Fri, 27 Aug 2021 12:24:13 -0400 Received: from liberator.sandeen.net (liberator.sandeen.net [10.0.0.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by sandeen.net (Postfix) with ESMTPSA id A06E879FC; Fri, 27 Aug 2021 11:23:00 -0500 (CDT) Subject: Re: [PATCH] mkfs.xfs.8: clarify DAX-vs-reflink restrictions in the mkfs.xfs man page To: "Darrick J. Wong" , Eric Sandeen Cc: xfs , Bill O'Donnell References: <59ebcf23-9e32-e219-ef8b-9aa7ab2444c2@redhat.com> <20210827154905.GP12640@magnolia> From: Eric Sandeen Message-ID: <8c478cd9-31cf-d659-0088-949519cf11bc@sandeen.net> Date: Fri, 27 Aug 2021 11:23:22 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210827154905.GP12640@magnolia> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 8/27/21 10:49 AM, Darrick J. Wong wrote: > On Fri, Aug 27, 2021 at 10:39:18AM -0500, Eric Sandeen wrote: >> Now that we have the tristate dax mount options, it is possible >> to enable DAX mode for non-reflinked files on a reflink-capable >> filesystem. Clarify this in the mkfs.xfs manpage. >> >> Reported-by: Bill O'Donnell >> Signed-off-by: Eric Sandeen >> --- >> >> diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8 >> index a7f70285..84ac50e8 100644 >> --- a/man/man8/mkfs.xfs.8 >> +++ b/man/man8/mkfs.xfs.8 >> @@ -316,12 +316,20 @@ option set. When the option >> is used, the reference count btree feature is not supported and reflink is >> disabled. >> .IP >> -Note: the filesystem DAX mount option ( >> +Note: the filesystem-wide DAX mount options ( >> .B \-o dax >> -) is incompatible with >> -reflink-enabled XFS filesystems. To use filesystem DAX with XFS, specify the >> +and >> +.B \-o dax=always >> +) are incompatible with >> +reflink-enabled XFS filesystems. To use filesystem-wide DAX with XFS, specify the >> .B \-m reflink=0 >> option to mkfs.xfs to disable the reflink feature. >> +Alternatey, use the > > "Alternately..." "Alternatively," > >> +.B \-o dax=inode >> +mount option to selectively enable DAX mode on non-reflinked files. > > /me wonders if this is dangerously close to wading into the muck that is > "Use dax=inode or even no dax option at all, then make sure nobody > shares your file's data blocks to set the DAX fsxattr flag on the file, > and /then/ you can have DAX." Perhaps I should drop most of it, and just wave hands vaguely at xfs.5? -Eric