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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C509EC4332F for ; Fri, 21 Jan 2022 02:36:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348449AbiAUCgI (ORCPT ); Thu, 20 Jan 2022 21:36:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244394AbiAUCgI (ORCPT ); Thu, 20 Jan 2022 21:36:08 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AEEBFC061574; Thu, 20 Jan 2022 18:36:07 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 55A02B81D84; Fri, 21 Jan 2022 02:36:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EEF61C340E0; Fri, 21 Jan 2022 02:36:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642732564; bh=7WwbHgXEEmyGk8VsUc9soyxxvD8Rd4CVOIzfWVbGxgg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TJWHvQOYkvpukFEO29VsctzeUshaTt9r4j2tPBeTNRkhlOAXQFmschOiLFwTw6Vgu kC1CNn/nzXp7xSsldL30IPcWqUdgLtC1WKXtNmnG11pqmtpicA1Hs++8V/A012/q7x 4mPI8QRzywjj+HqybFxooxhslpzJjRRCyU3i5ec7nJwO/9wPnVvvOmpe9SQDa/dkM7 6rE7wpJ6XE3K4YGGCFPBxob2vexcsDcGHAPAAmhcnrY8Q5+rPbXfAIaqLMpL1a3PWT I0CXVQab1nmPAnsYio6Mnl6xT1TdoYFeBAUlqZdOlZCK6LiWewa1WyG/oOjDmSxpES btPl9CCCv+54w== Date: Thu, 20 Jan 2022 18:36:03 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: Eric Biggers , Christoph Hellwig , linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, Theodore Ts'o , Jaegeuk Kim , Chao Yu Subject: Re: [PATCH v10 0/5] add support for direct I/O with fscrypt using blk-crypto Message-ID: <20220121023603.GH13563@magnolia> References: <20220120071215.123274-1-ebiggers@kernel.org> <20220120171027.GL13540@magnolia> <20220120210027.GQ13540@magnolia> <20220120220414.GH59729@dread.disaster.area> <20220120235755.GI59729@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220120235755.GI59729@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Jan 21, 2022 at 10:57:55AM +1100, Dave Chinner wrote: > On Thu, Jan 20, 2022 at 02:48:52PM -0800, Eric Biggers wrote: > > On Fri, Jan 21, 2022 at 09:04:14AM +1100, Dave Chinner wrote: > > > On Thu, Jan 20, 2022 at 01:00:27PM -0800, Darrick J. Wong wrote: > > > > On Thu, Jan 20, 2022 at 12:39:14PM -0800, Eric Biggers wrote: > > > > > On Thu, Jan 20, 2022 at 09:10:27AM -0800, Darrick J. Wong wrote: > > > > > > On Thu, Jan 20, 2022 at 12:30:23AM -0800, Christoph Hellwig wrote: > > > > > > > On Wed, Jan 19, 2022 at 11:12:10PM -0800, Eric Biggers wrote: > > > > > > > > > > > > > > > > Given the above, as far as I know the only remaining objection to this > > > > > > > > patchset would be that DIO constraints aren't sufficiently discoverable > > > > > > > > by userspace. Now, to put this in context, this is a longstanding issue > > > > > > > > with all Linux filesystems, except XFS which has XFS_IOC_DIOINFO. It's > > > > > > > > not specific to this feature, and it doesn't actually seem to be too > > > > > > > > important in practice; many other filesystem features place constraints > > > > > > > > on DIO, and f2fs even *only* allows fully FS block size aligned DIO. > > > > > > > > (And for better or worse, many systems using fscrypt already have > > > > > > > > out-of-tree patches that enable DIO support, and people don't seem to > > > > > > > > have trouble with the FS block size alignment requirement.) > > > > > > > > > > > > > > It might make sense to use this as an opportunity to implement > > > > > > > XFS_IOC_DIOINFO for ext4 and f2fs. > > > > > > > > > > > > Hmm. A potential problem with DIOINFO is that it doesn't explicitly > > > > > > list the /file/ position alignment requirement: > > > > > > > > > > > > struct dioattr { > > > > > > __u32 d_mem; /* data buffer memory alignment */ > > > > > > __u32 d_miniosz; /* min xfer size */ > > > > > > __u32 d_maxiosz; /* max xfer size */ > > > > > > }; > > > > > > > > > > Well, the comment above struct dioattr says: > > > > > > > > > > /* > > > > > * Direct I/O attribute record used with XFS_IOC_DIOINFO > > > > > * d_miniosz is the min xfer size, xfer size multiple and file seek offset > > > > > * alignment. > > > > > */ > > > > > > > > > > So d_miniosz serves that purpose already. > > > > > > > > > > > > > > > > > Since I /think/ fscrypt requires that directio writes be aligned to file > > > > > > block size, right? > > > > > > > > > > The file position must be a multiple of the filesystem block size, yes. > > > > > Likewise for the "minimum xfer size" and "xfer size multiple", and the "data > > > > > buffer memory alignment" for that matter. So I think XFS_IOC_DIOINFO would be > > > > > good enough for the fscrypt direct I/O case. > > > > > > > > Oh, ok then. In that case, just hoist XFS_IOC_DIOINFO to the VFS and > > > > add a couple of implementations for ext4 and f2fs, and I think that'll > > > > be enough to get the fscrypt patchset moving again. > > > > > > On the contrary, I'd much prefer to see this information added to > > > statx(). The file offset alignment info is a property of the current > > > file (e.g. XFS can have different per-file requirements depending on > > > whether the file data is hosted on the data or RT device, etc) and > > > so it's not a fixed property of the filesystem. > > > > > > statx() was designed to be extended with per-file property > > > information, and we already have stuff like filesystem block size in > > > that syscall. Hence I would much prefer that we extend it with the > > > DIO properties we need to support rather than "create" a new VFS > > > ioctl to extract this information. We already have statx(), so let's > > > use it for what it was intended for. Eh, ok. Let's do that instead. > > > > > > > I assumed that XFS_IOC_DIOINFO *was* per-file. XFS's *implementation* of it > > looks at the filesystem only, > > You've got that wrong. > > case XFS_IOC_DIOINFO: { > >>>>>> struct xfs_buftarg *target = xfs_inode_buftarg(ip); > struct dioattr da; > > da.d_mem = da.d_miniosz = target->bt_logical_sectorsize; > > xfs_inode_buftarg() is determining which block device the inode is > storing it's data on, so the returned dioattr values can be > different for different inodes in the filesystem... > > It's always been that way since the early Irix days - XFS RT devices > could have very different IO constraints than the data device and > DIO had to conform to the hardware limits underlying the filesystem. > Hence the dioattr information has -always- been per-inode > information. > > > (Per-file state is required for encrypted > > files. It's also required for other filesystem features; e.g., files that use > > compression or fs-verity don't support direct I/O at all.) > > Which is exactly why is should be a property of statx(), rather than > try to re-use a ~30 year old filesystem specific API from a > different OS that was never intended to indicate things like "DIO > not supported on this file at all".... Heh. You mean like ALLOCSP? Ok ok point taken. > We've been bitten many times by this "lift a rarely used filesystem > specific ioctl to the VFS because it exists" method of API > promotion. It almost always ends up in us discovering further down > the track that there's something wrong with the API, it doesn't > quite do what we need, we have to extend it anyway, or it's just > plain borken, etc. And then we have to create a new, fit for purpose > API anyway, and there's two VFS APIs we have to maintain forever > instead of just one... > > Can we learn from past mistakes this time instead of repeating them > yet again? Sure. How's this? I couldn't think of a real case of directio requiring different alignments for pos and bytecount, so the only real addition here is the alignment requirements for best performance. struct statx { ... /* 0x90 */ __u64 stx_mnt_id; /* Memory buffer alignment required for directio, in bytes. */ __u32 stx_dio_mem_align; /* File range alignment required for directio, in bytes. */ __u32 stx_dio_fpos_align_min; /* 0xa0 */ /* File range alignment needed for best performance, in bytes. */ __u32 stx_dio_fpos_align_opt; /* Maximum size of a directio request, in bytes. */ __u32 stx_dio_max_iosize; __u64 __spare3[11]; /* Spare space for future expansion */ /* 0x100 */ }; Along with: #define STATX_DIRECTIO 0x00001000U /* Want/got directio geometry */ How about that? --D > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com