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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 0DF20C71155 for ; Tue, 1 Dec 2020 03:38:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D30A6207DE for ; Tue, 1 Dec 2020 03:38:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727770AbgLADiL (ORCPT ); Mon, 30 Nov 2020 22:38:11 -0500 Received: from sandeen.net ([63.231.237.45]:60626 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727719AbgLADiL (ORCPT ); Mon, 30 Nov 2020 22:38:11 -0500 Received: from liberator.sandeen.net (liberator.sandeen.net [10.0.0.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by sandeen.net (Postfix) with ESMTPSA id 9991D14A06; Mon, 30 Nov 2020 21:37:15 -0600 (CST) To: "Theodore Y. Ts'o" Cc: David Howells , "Darrick J. Wong" , linux-fsdevel@vger.kernel.org References: <20201125212523.GB14534@magnolia> <33d38621-b65c-b825-b053-eda8870281d1@sandeen.net> <1942931.1606341048@warthog.procyon.org.uk> <20201201032051.GK5364@mit.edu> From: Eric Sandeen Subject: Re: Clarification of statx->attributes_mask meaning? Message-ID: Date: Mon, 30 Nov 2020 21:37:29 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201201032051.GK5364@mit.edu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 11/30/20 9:20 PM, Theodore Y. Ts'o wrote: > On Mon, Nov 30, 2020 at 05:29:47PM -0600, Eric Sandeen wrote: >> On 11/25/20 3:50 PM, David Howells wrote: >>> Darrick J. Wong wrote: >>> >>>> mask=1 bit=0: "attribute not set on this file" >>>> mask=1 bit=1: "attribute is set on this file" >>>> mask=0 bit=0: "attribute doesn't fit into the design of this fs" >>> >>> Or is "not supported by the filesystem driver in this kernel version". >> >> For a concrete example, let's talk about the DAX statx attribute. >> >> If the kernel is configured w/o DAX support, should the DAX attr be in the mask? >> If the block device has no DAX support, should the DAX attr be in the mask? >> If the filesystem is mounted with dax=never, should the DAX attr be in the mask? >> >> About to send a patch for xfs which answers "no" to all of those, but I'm still >> not quite sure if that's what's expected. I'll be sure to cc: dhowells, Ira, and >> others who may care... > > So you're basically proposing that the mask is indicating whether or > not the attribute is supported by a particular on-disk file system > image and/or how it is currently configured/mounted --- and not > whether an attribute is supported by a particular file system > *implementation*. Well, not trying to propose anything new, just trying to understand the intent of the mask to get it set correctly for the dax attribute. > For example, for ext4, if the extents feature is not enabled (for > example, when the ext4 file system code is used mount a file system > whose feature bitmask is consistent with a historic ext2 file system) > the extents flag should be cleared from the attribute mask? > > This adds a fair amount of complexity to the file system since there > are a number of flags that might have similar issues --- for example, > FS_CASEFOLD_FL, and I could imagine for some file systems, where > different revisions might or might not support reflink FS_NOCOW_FL, > etc. I've been told that I'm over-complicating this, yes. > We should be really clear how applications are supposed to use the > attributes_mask. Does it mean that they will always be able to set a > flag which is set in the attribute mask? That can't be right, since > there will be a number of flags that may have some more complex checks > (you must be root, or the file must be zero length, etc.) I'm a bit > unclear about what are the useful ways in which an attribute_mask can > be used by a userspace application --- and under what circumstances > might an application be depending on the semantics of attribute_mask, > so we don't accidentally give them an opportunity to complain and > whine, thus opening ourselves to another O_PONIES controversy. Hah, indeed. Sorry if I've over-complicated this, I'm honestly just confused now. -Eric