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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 01639C433DF for ; Mon, 6 Jul 2020 14:32:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D420220715 for ; Mon, 6 Jul 2020 14:32:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="lLLTcpYo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729245AbgGFOcU (ORCPT ); Mon, 6 Jul 2020 10:32:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56292 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729171AbgGFOcU (ORCPT ); Mon, 6 Jul 2020 10:32:20 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD6F7C061755; Mon, 6 Jul 2020 07:32:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=EwRW73shu2IKaqwwBXGdBFaT6QYUJm5UYLekvD4vwS0=; b=lLLTcpYoSD5PpyNLbnXTbjoIA9 4suCDa81YT0EEaz4cW1srEqKFWuGaYeA1plgRjsfDXWOZT+p0jeMWZRzBSlZUNCiW9xzY2G+31lVB XJD4LLXG/qg1RxSIsgrEf00z6MR8q+wQgBSEzH4qg5NEYNW18NTwRpN5zVMqJmXHJoSBevmtzS+Y1 KTMYa/J34CAPdVNoMfKQEoZMJDNEcO1eEwkhhtGX3GwcMW242hIRLmnfd59FU5lZRGU67EmcnbjWy 5OeKclqo9JScO2avW8guw3tHuk8n5ZIN72H65ae+5ZknuOEESp3AOfuHHJtLIApuw5SUPZoA7ZRta cyMXfJIw==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jsSAC-0004pr-4L; Mon, 06 Jul 2020 14:32:08 +0000 Date: Mon, 6 Jul 2020 15:32:08 +0100 From: Matthew Wilcox To: Jens Axboe Cc: Kanchan Joshi , viro@zeniv.linux.org.uk, bcrl@kvack.org, hch@infradead.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com, linux-fsdevel@vger.kernel.org, mb@lightnvm.io, linux-kernel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-block@vger.kernel.org, Selvakumar S , Nitesh Shetty , Javier Gonzalez Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append Message-ID: <20200706143208.GA25523@casper.infradead.org> References: <1593974870-18919-1-git-send-email-joshi.k@samsung.com> <1593974870-18919-5-git-send-email-joshi.k@samsung.com> <20200705210947.GW25523@casper.infradead.org> <239ee322-9c38-c838-a5b2-216787ad2197@kernel.dk> <20200706141002.GZ25523@casper.infradead.org> <4a9bf73e-f3ee-4f06-7fad-b8f8861b0bc1@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4a9bf73e-f3ee-4f06-7fad-b8f8861b0bc1@kernel.dk> Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Jul 06, 2020 at 08:27:17AM -0600, Jens Axboe wrote: > On 7/6/20 8:10 AM, Matthew Wilcox wrote: > > On Sun, Jul 05, 2020 at 03:12:50PM -0600, Jens Axboe wrote: > >> On 7/5/20 3:09 PM, Matthew Wilcox wrote: > >>> On Sun, Jul 05, 2020 at 03:00:47PM -0600, Jens Axboe wrote: > >>>> On 7/5/20 12:47 PM, Kanchan Joshi wrote: > >>>>> From: Selvakumar S > >>>>> > >>>>> For zone-append, block-layer will return zone-relative offset via ret2 > >>>>> of ki_complete interface. Make changes to collect it, and send to > >>>>> user-space using cqe->flags. > > > >>> I'm surprised you aren't more upset by the abuse of cqe->flags for the > >>> address. > >> > >> Yeah, it's not great either, but we have less leeway there in terms of > >> how much space is available to pass back extra data. > >> > >>> What do you think to my idea of interpreting the user_data as being a > >>> pointer to somewhere to store the address? Obviously other things > >>> can be stored after the address in the user_data. > >> > >> I don't like that at all, as all other commands just pass user_data > >> through. This means the application would have to treat this very > >> differently, and potentially not have a way to store any data for > >> locating the original command on the user side. > > > > I think you misunderstood me. You seem to have thought I meant > > "use the user_data field to return the address" when I actually meant > > "interpret the user_data field as a pointer to where userspace > > wants the address stored". > > It's still somewhat weird to have user_data have special meaning, you're > now having the kernel interpret it while every other command it's just > an opaque that is passed through. > > But it could of course work, and the app could embed the necessary > u32/u64 in some other structure that's persistent across IO. If it > doesn't have that, then it'd need to now have one allocated and freed > across the lifetime of the IO. > > If we're going that route, it'd be better to define the write such that > you're passing in the necessary information upfront. In syscall terms, > then that'd be something ala: > > ssize_t my_append_write(int fd, const struct iovec *iov, int iovcnt, > off_t *offset, int flags); > > where *offset is copied out when the write completes. That removes the > need to abuse user_data, with just providing the storage pointer for the > offset upfront. That works for me! In io_uring terms, would you like to see that done as adding: union { __u64 off; /* offset into file */ + __u64 *offp; /* appending writes */ __u64 addr2; };