Return-Path: Received: from dmz-mailsec-scanner-6.mit.edu ([18.7.68.35]:55450 "EHLO dmz-mailsec-scanner-6.mit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731121AbeLUQ2b (ORCPT ); Fri, 21 Dec 2018 11:28:31 -0500 Date: Fri, 21 Dec 2018 11:28:13 -0500 From: "Theodore Y. Ts'o" To: Matthew Wilcox Cc: Christoph Hellwig , Dave Chinner , "Darrick J. Wong" , Eric Biggers , linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, Jaegeuk Kim , Victor Hsieh , Chandan Rajendra , Linus Torvalds Subject: Re: [PATCH v2 01/12] fs-verity: add a documentation file Message-ID: <20181221162813.GB26547@mit.edu> References: <20181219071420.GC2628@infradead.org> <20181219021953.GD31274@dastard> <20181219193005.GB6889@mit.edu> <20181219213552.GO6311@dastard> <20181220220158.GC2360@mit.edu> <20181221070447.GA21687@infradead.org> <20181221154714.GA26547@mit.edu> <20181221155354.GC10600@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181221155354.GC10600@bombadil.infradead.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Dec 21, 2018 at 07:53:54AM -0800, Matthew Wilcox wrote: > In contrast to "we'll just fix it up later" (which usually applies > to in-kernel interfaces), we have a policy of not breaking userspace, > so accepting this interface means setting it in stone. We should get > it right. I'm not convinced it's a "fix", but my point is that if later on you want to add extra complexity transforming ioctl(fd, FS_IOC_ENABLE_VERITY); so it does the equivalent of ioctl(fd, FS_IOC_ENABLE_VERITY_NOW_WITH_EXTRA_USELESS_COMPLEXITY, fd, sizeof_data, sizeof_verity_data); it adds essentially no complexity to provide this backwards compatibility. But if we need to implement FS_IOC_ENABLE_VERITY_NOW_WITH_EXTRA_USELESS_COMPLEXITY *now*, we gain nothing, other than pushing back when fsverity lands upstream. We'd have to provide that backwards compatibility interface anyway, since there are a lot of users for that existing interface. So why? - Ted