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 2B0ABC433F5 for ; Thu, 20 Jan 2022 20:39:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377658AbiATUjS (ORCPT ); Thu, 20 Jan 2022 15:39:18 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:39686 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229701AbiATUjS (ORCPT ); Thu, 20 Jan 2022 15:39:18 -0500 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 dfw.source.kernel.org (Postfix) with ESMTPS id B045D61834; Thu, 20 Jan 2022 20:39:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9512C340E0; Thu, 20 Jan 2022 20:39:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1642711156; bh=xHyJV2OF1Wme9jGp3aO4nKBDG16B8D+4M9ewndf2eJc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mXLj0tywklYTXnw6izq3AIlPI96bKEb6CLyl+fLbQESaYmG1kISbixIyFAv/S46Yt c3w5LXM0tWf7J4YyUpYmBMvJfRLefA1hgMgn0qeGwsxM2fMFZcmVdHiBwREeqoh+Bj U5cKYdGF1Zwo5HRRQ/D6nYOFBwCGrr26BzMfnPtcGXUP+Wv4ZGHpTCuuhQ2JBijA4h 4aoYP4S5J+7wdukl7VBSaO/CKCgyDxK0dy/8QciVjrp0hOtcXOMuN3kyj1aD3vBBZn oy6iTnANsohSdKfd13BW8GoWBfQ63urh/ZWj8SglSPCOw4zdk3yK2mi4cq2SLUmDAU LHZ1eZC58PDsg== Date: Thu, 20 Jan 2022 12:39:14 -0800 From: Eric Biggers To: "Darrick J. Wong" Cc: 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, Dave Chinner , 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: References: <20220120071215.123274-1-ebiggers@kernel.org> <20220120171027.GL13540@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220120171027.GL13540@magnolia> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org 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. The real question is whether there are any direct I/O implementations where XFS_IOC_DIOINFO would *not* be good enough, for example due to "xfer size multiple" != "file seek offset alignment" being allowed. In that case we would need to define a new ioctl that is more general (like the one you described below) rather than simply uplifting XFS_IOC_DIOINFO. More general is nice, but it's not helpful if no one will actually use the extra information. So we need to figure out what is actually useful. > How about something like this: > > struct dioattr2 { > __u32 d_mem; /* data buffer memory alignment */ > __u32 d_miniosz; /* min xfer size */ > __u32 d_maxiosz; /* max xfer size */ > > /* file range must be aligned to this value */ > __u32 d_min_fpos; > > /* for optimal performance, align file range to this */ > __u32 d_opt_fpos; > > __u32 d_padding[11]; > }; > - Eric