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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 428A5C433DB for ; Thu, 24 Dec 2020 06:42:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F2E32227BF for ; Thu, 24 Dec 2020 06:42:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725747AbgLXGmJ (ORCPT ); Thu, 24 Dec 2020 01:42:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725613AbgLXGmI (ORCPT ); Thu, 24 Dec 2020 01:42:08 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69174C061794; Wed, 23 Dec 2020 22:41:28 -0800 (PST) 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=hgZ+lZNP3B/K9Oj/s5udXyrBDVF5xZJ71bYP1nixZdo=; b=hzjxM2aGVedqOqTPaeLJKWYuY4 xkqiFVFpQKWkgqEySPTCLiSvWvcEJrgRLsJBOnrS0QZdfm4dsSOXZeO0PNLab6ggKCBq1lw6nS3kW Y3WaTFZ3ODCAIHwpPam/g5eYytVyG9hqXEC7GPEvByE+eg/g0kafrqgdDkSIVH2HW9VYEuJ8mRIkc w8qFJdvjTIWFM9bOal30Yib0rTy3vrCUR/hyI4lFqoeN/ROgowBMVqDPpJTNzgpcOcabaesZubCUI HkInEHpdkOK6FMxwC/PdZmtaPCsBloa68FjEumpKaKfc+q+vT15CVF5bXkEMkQSnUvd4YD+3SEbZo nG0RhV+w==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1ksKJL-0000uK-Pw; Thu, 24 Dec 2020 06:41:19 +0000 Date: Thu, 24 Dec 2020 06:41:19 +0000 From: Christoph Hellwig To: Pavel Begunkov Cc: dgilbert@interlog.com, James Bottomley , Christoph Hellwig , 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 Subject: Re: [PATCH v1 0/6] no-copy bvec Message-ID: <20201224064119.GA3048@infradead.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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Wed, Dec 23, 2020 at 08:32:45PM +0000, Pavel Begunkov wrote: > 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? None of the SCSI Command mentions above are supported by Linux, nevermind mapped to struct scatterlist.