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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 4B76AC433E6 for ; Wed, 23 Dec 2020 20:37:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 204942253A for ; Wed, 23 Dec 2020 20:37:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726686AbgLWUgw (ORCPT ); Wed, 23 Dec 2020 15:36:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34670 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726279AbgLWUgv (ORCPT ); Wed, 23 Dec 2020 15:36:51 -0500 Received: from mail-wr1-x42e.google.com (mail-wr1-x42e.google.com [IPv6:2a00:1450:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2ADCBC06179C; Wed, 23 Dec 2020 12:36:11 -0800 (PST) Received: by mail-wr1-x42e.google.com with SMTP id d13so345851wrc.13; Wed, 23 Dec 2020 12:36:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=a0rpAb93KEzfxlmUoYJd4BCt58+pD6nzkkuli/XS38E=; b=GL9+LliYfL8/uuo3thjXfhFVPCDzOYuzbT/YTw/gXSU+e8byMr6IWG4JRI9A8JE1Rn J9F+Ir8ph1gDvr7NIwbitZrbdOvoFkdCskpdPUe0+u+xQkaaZt1QjU+jmYdbcxRaLdSH uyzsd+GuiBVEMIh8kdtKqtCyww+Q/F2QGVjMQfLw/YdsaOdwrZPPB1jZXqCg0eW9pMce /temjc8dJPt94GBmENn8B/W+ZvU8MQv6D+CtSbHI4OCSEpVViXkVmOlRHPaEUhoYibtM mJZ/zLY5P4eiA5GmYsPXYOEs3WT9tS0nn9n1wYh3Gl1ORDTb0hYgjidc1+25qIGnkAJ8 wCeA== 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:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=a0rpAb93KEzfxlmUoYJd4BCt58+pD6nzkkuli/XS38E=; b=oY8+TdHU8TM74A2oRhkyR0SVWc0mWjBhP60BzAYU2z04w5CRg3Rdd17PfokXC1AgJZ RXYYnmPgYz7LcPkfiF8cGO7E1S4yZ6zM6nPgX7QF1vq3h1oRcHhuwdZy86xSdHCIZERA 4g4SSoCUS1HzNcy3oZOcQdwddq07035NVwujouMwMj5hTHJOW724Bgn+qbEGiGouAIXC Ov49LspcYQzqGr//MTkK/VmLDaEs6A4X6wWkCkx+C1YLyZ3sRA0LKl1IGUbBywjZUp/m oGEJ/e/t2RjWFcacQB4oGg0G9dgGhwitJzTbMZj7CqYD2MC7j81LC8D6IAxmNdz4OH/V fRpw== X-Gm-Message-State: AOAM532fysX1+lJ3THoG4xbdi1GDTSgcq7sz5cjjmTVZOR3WpQXUJhXl Y81pWBwdiALG/CBeziD5cCSHg771b7GcRA== X-Google-Smtp-Source: ABdhPJyfdcpevW4c5rLF9fw3eGxFPW+d0c0i5c8SoYyvopbDxArb44ULVgyephWBuR+3XrCfl6GgOA== X-Received: by 2002:adf:9d82:: with SMTP id p2mr19030926wre.330.1608755769486; Wed, 23 Dec 2020 12:36:09 -0800 (PST) Received: from [192.168.8.148] ([85.255.233.85]) by smtp.gmail.com with ESMTPSA id n9sm36389523wrq.41.2020.12.23.12.36.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Dec 2020 12:36:09 -0800 (PST) Subject: Re: [PATCH v1 0/6] no-copy bvec To: dgilbert@interlog.com, James Bottomley , Christoph Hellwig Cc: Ming Lei , linux-block@vger.kernel.org, Jens Axboe , Matthew Wilcox , Johannes Weiner , Alexander Viro , "Darrick J . Wong" , "Martin K . Petersen" , Jonathan Corbet , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, target-devel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-doc@vger.kernel.org References: <20201215014114.GA1777020@T590> <103235c1-e7d0-0b55-65d0-013d1a09304e@gmail.com> <20201215120357.GA1798021@T590> <20201222141112.GE13079@infradead.org> <933030f0-e428-18fd-4668-68db4f14b976@gmail.com> <20201223155145.GA5902@infradead.org> <8abc56c2-4db8-5ee3-ab2d-8960d0eeeb0d@interlog.com> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Message-ID: Date: Wed, 23 Dec 2020 20:32:45 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <8abc56c2-4db8-5ee3-ab2d-8960d0eeeb0d@interlog.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 23/12/2020 20:23, Douglas Gilbert wrote: > On 2020-12-23 11:04 a.m., James Bottomley wrote: >> On Wed, 2020-12-23 at 15:51 +0000, Christoph Hellwig wrote: >>> On Wed, Dec 23, 2020 at 12:52:59PM +0000, Pavel Begunkov wrote: >>>> Can scatterlist have 0-len entries? Those are directly translated >>>> into bvecs, e.g. in nvme/target/io-cmd-file.c and >>>> target/target_core_file.c. I've audited most of others by this >>>> moment, they're fine. >>> >>> For block layer SGLs we should never see them, and for nvme neither. >>> I think the same is true for the SCSI target code, but please double >>> check. >> >> Right, no-one ever wants to see a 0-len scatter list entry.  The reason >> is that every driver uses the sgl to program the device DMA engine in >> the way NVME does.  a 0 length sgl would be a dangerous corner case: >> some DMA engines would ignore it and others would go haywire, so if we >> ever let a 0 length list down into the driver, they'd have to >> understand the corner case behaviour of their DMA engine and filter it >> accordingly, which is why we disallow them in the upper levels, since >> they're effective nops anyway. > > When using scatter gather lists at the far end (i.e. on the storage device) > the T10 examples (WRITE SCATTERED and POPULATE TOKEN in SBC-4) explicitly > allow the "number of logical blocks" in their sgl_s to be zero and state > that it is _not_ to be considered an error. It's fine for my case unless it leaks them out of device driver to the net/block layer/etc. Is it? -- Pavel Begunkov