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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 D911DC34022 for ; Wed, 19 Feb 2020 04:10:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCDBD2467A for ; Wed, 19 Feb 2020 04:10:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726510AbgBSEKf (ORCPT ); Tue, 18 Feb 2020 23:10:35 -0500 Received: from mail104.syd.optusnet.com.au ([211.29.132.246]:57800 "EHLO mail104.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726826AbgBSEKf (ORCPT ); Tue, 18 Feb 2020 23:10:35 -0500 Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 1456C7EAFAA; Wed, 19 Feb 2020 15:10:34 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j4Ggz-0005k3-8Z; Wed, 19 Feb 2020 15:10:33 +1100 Date: Wed, 19 Feb 2020 15:10:33 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: Christoph Hellwig , linux-xfs@vger.kernel.org, Allison Collins Subject: Re: [PATCH 23/31] xfs: properly type the buffer field in struct xfs_fsop_attrlist_handlereq Message-ID: <20200219041033.GK10776@dread.disaster.area> References: <20200217125957.263434-1-hch@lst.de> <20200217125957.263434-24-hch@lst.de> <20200217235315.GY10776@dread.disaster.area> <20200218153924.GB21780@lst.de> <20200219005847.GG9506@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219005847.GG9506@magnolia> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=zAxSp4fFY/GQY8/esVNjqw==:117 a=zAxSp4fFY/GQY8/esVNjqw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=l697ptgUJYAA:10 a=7-415B0cAAAA:8 a=QyZR4WbsfNoAadtN2jQA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Feb 18, 2020 at 04:58:47PM -0800, Darrick J. Wong wrote: > On Tue, Feb 18, 2020 at 04:39:24PM +0100, Christoph Hellwig wrote: > > On Tue, Feb 18, 2020 at 10:53:16AM +1100, Dave Chinner wrote: > > > > diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h > > > > index ae77bcd8c05b..21920f613d42 100644 > > > > --- a/fs/xfs/libxfs/xfs_fs.h > > > > +++ b/fs/xfs/libxfs/xfs_fs.h > > > > @@ -597,7 +597,7 @@ typedef struct xfs_fsop_attrlist_handlereq { > > > > struct xfs_attrlist_cursor pos; /* opaque cookie, list offset */ > > > > __u32 flags; /* which namespace to use */ > > > > __u32 buflen; /* length of buffer supplied */ > > > > - void __user *buffer; /* returned names */ > > > > + struct xfs_attrlist __user *buffer;/* returned names */ > > > > } xfs_fsop_attrlist_handlereq_t; > > > > > > This changes the userspace API, right? So, in theory, it could break > > > compilation of userspace applications that treat it as an attrlist_t > > > and don't specifically cast the assignment because it's currently > > > a void pointer? > > > > IFF userspace was using this header it would change the API. But > > userspace uses the libattr definition exclusively. > > Assuming most userspace will use libhandle (and not call the ioctl > directly) then this "shouldn't" be a problem because libhandle treats > the attrlist buffer as a void pointer. There's a lot of "if's" there. :/ All I'm asking for is that the changes are documented as known and intentional so that we don't end up a couple of years down the track wondering WTF we were thinking when we made this change... > (I dunno, how difficult /is/ it to say "program to the library, not the > kernel ABI" here?) The xfsctl(3) man page already says this: XFS_IOC_PATH_TO_HANDLE XFS_IOC_PATH_TO_FSHANDLE XFS_IOC_FD_TO_HANDLE XFS_IOC_OPEN_BY_HANDLE XFS_IOC_READLINK_BY_HANDLE XFS_IOC_ATTR_LIST_BY_HANDLE XFS_IOC_ATTR_MULTI_BY_HANDLE XFS_IOC_FSSETDM_BY_HANDLE These are all interfaces that are used to implement various libhandle functions (see open_by_handle(3)). They are all subject to change and should not be called directly by applications. and the open_by_handle(3) man page says "use libhandle to access these functions". Cheers, Dave. -- Dave Chinner david@fromorbit.com