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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 57F4EC433E0 for ; Mon, 6 Jul 2020 14:27:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D00220722 for ; Mon, 6 Jul 2020 14:27:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="Rc42P7/I" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729379AbgGFO1U (ORCPT ); Mon, 6 Jul 2020 10:27:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55516 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729349AbgGFO1U (ORCPT ); Mon, 6 Jul 2020 10:27:20 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21F97C08C5DF for ; Mon, 6 Jul 2020 07:27:20 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id t27so28090279ill.9 for ; Mon, 06 Jul 2020 07:27:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=5pd6A1qQMmxK9eO0hxzM1d+CDCdrMgAG1MKgD8BGrbY=; b=Rc42P7/IdLVkITZMFrzCbZkYZ4ZIgvn2LtkG42gtQLhGoZsjoJcXj0BSWaI25x8o8R 7itie3dpxY6qcuJnSy8nE8tS8E9MyEUREajrdVW4SYsLSI/7aE5+4pHPiOfgsN7XMsdA G9dk4PCCutn9VfgT+wlNLDcZs1eoiBi29U6hIq/oTNbaMXCdyIODVqHtVQVCsZbVRirr Bd7Mmu+AgPx2jL0ok/xTe+wfcifeYyyHPyFtGq7CtCL4KDq0TwDaSXuXu8CNt6ve4aFY bFm05TkOE/UqeqqENDY8gGCu6Hk5MMGNNZ1fnpT1oxDn+iKT9OWA8Ml1WieaD0HAt2kd fqrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=5pd6A1qQMmxK9eO0hxzM1d+CDCdrMgAG1MKgD8BGrbY=; b=ClMAquJh6c0eviz4Bq0ocQTDqfXioMpifl70SN5WJAbfKZ3XmKJr1ht0DGgvNd0/e8 PCkdKCvSVS6eJG++m+Sl5+SgIzNn7HozReMRux0/wyyndnhe2qUM2V0nPU+CGydf53Ko 20oJNxE0c2N+6UR9F1T1ACfTy46HM2Yqk/eEOjhLYp95RuFP4L2p6grcWEojiF87iBpQ +QDH7yA+uCkKFbJkXhH9leVC7wO9HAXRJuMGGNcJxB8MQ4g9SLh5QqpUC5hpQLJRQp39 UOit5GI1mZnw56CnOSyPwIUkVP62I2pQxL0RoXNINrAMXrsR7UMi/mohbFASQCG6uo3x HgAw== X-Gm-Message-State: AOAM532AufNVBgrfIji2gBUvYlbOiNYf320e/xnjZCrcrwik0Th42Ea/ B7thXfboTt6OTgy4qMOzZdRWqA== X-Google-Smtp-Source: ABdhPJytwi3Jr/FCbXzOMe56zwLXCUJGMaAswEThWlUWh8Rtp741kwbuv/W0FRFpufAvVJHK0JmMjw== X-Received: by 2002:a05:6e02:13a9:: with SMTP id h9mr31133265ilo.232.1594045639434; Mon, 06 Jul 2020 07:27:19 -0700 (PDT) Received: from [192.168.1.58] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id f76sm11518888ilg.62.2020.07.06.07.27.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Jul 2020 07:27:18 -0700 (PDT) Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append To: Matthew Wilcox 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 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> From: Jens Axboe Message-ID: <4a9bf73e-f3ee-4f06-7fad-b8f8861b0bc1@kernel.dk> Date: Mon, 6 Jul 2020 08:27:17 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200706141002.GZ25523@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. -- Jens Axboe