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=-5.6 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 A080CC4338F for ; Tue, 24 Aug 2021 09:48:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7A614613AB for ; Tue, 24 Aug 2021 09:48:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235658AbhHXJtT (ORCPT ); Tue, 24 Aug 2021 05:49:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235566AbhHXJtT (ORCPT ); Tue, 24 Aug 2021 05:49:19 -0400 Received: from mail-wr1-x42c.google.com (mail-wr1-x42c.google.com [IPv6:2a00:1450:4864:20::42c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1212C061757; Tue, 24 Aug 2021 02:48:34 -0700 (PDT) Received: by mail-wr1-x42c.google.com with SMTP id u16so30365546wrn.5; Tue, 24 Aug 2021 02:48:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=VG94zlDLd3x883YtDNmS9uT8EWoP3KBY06pFhvdSQaI=; b=CQBHBFnAtD6mkMLpOtKO9RFLxkb80vT2+QR+L1QtkN1NSsBESWSjsGq7Gl3eNihgUj sohg42ziimu0GKUktXRu/n1wmo4Ly/CGcR5wmuzMPQpfyYbwjukwoaaVIwHz8PvxH3bI w+NNRleGhgeMKWD96nblF42S7UjCi/vdng19ENXuB0eGlOEKvsp5z8M/3Ut6aGdAu0nR U7jVUAbgQ6tUngIOJhK8a5svIeigV5spkKSgEnv9F7Lt76TXf1NRFBqiza4jmh1442ld vndsPFoOq1L2DEqd0nUHv0EIdMlCCkN7tebOGe3IpNC6zQ2UJ/SF1gGA/vQtmhqJ0FOs DLeg== 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=VG94zlDLd3x883YtDNmS9uT8EWoP3KBY06pFhvdSQaI=; b=ruXZ3oBuFQHwZVddpU4er3tpx/jCd5yylCaaG++AfYLKju5WMjrzd75qeAHfZ3HClv xPGJQrbUvSuZ3QVj1ltnMgxF0NSSco/vqQRVPwpFgDz7wr62ayA6zI/Qm+noxdVfg/az wAbw/pBYHPQVQvRmp0LAm5yNcRAM64whb7b3fJoLNeqiZpoYJ2j9hMnbkqPWtG0aE25k rYXZ63SqB77WQMUv5bHXg9LCpMxFXk2sVH6GiBo3qpxfwi0R76w4pOkaJ8YS3AgHl+12 8jxffs22FyP3UufskiXoakb7TkAUAdtWospm+NgFWgDKrnBpNqfASYRW2yNX7zcfo48B ZPlg== X-Gm-Message-State: AOAM530939PQM/XBM2tOA+powM3BIbDo/n0ElAxAGBZ5Fi3MQ7Y6w3SY pTOJmX3+RspDGViBmhgjQOM= X-Google-Smtp-Source: ABdhPJxyPG8kH/z9iRJ/24fUQi24iEEOETzdkO/opyfzwMptxtbC5Qe1Wl+UHbqNLZhuzxy7tZ3cgQ== X-Received: by 2002:adf:f8c8:: with SMTP id f8mr18824817wrq.204.1629798513621; Tue, 24 Aug 2021 02:48:33 -0700 (PDT) Received: from [192.168.8.197] ([85.255.232.113]) by smtp.gmail.com with ESMTPSA id z7sm1761767wmi.4.2021.08.24.02.48.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Aug 2021 02:48:33 -0700 (PDT) Subject: Re: [PATCH v3 0/4] open/accept directly into io_uring fixed file table To: Jens Axboe , Josh Triplett Cc: io-uring@vger.kernel.org, "David S . Miller" , Jakub Kicinski , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Stefan Metzmacher References: <7fa72eec-9222-60eb-9ec6-e4b6efbfc5fb@kernel.dk> <59494bda-f804-4185-dd7d-4827b14bae61@kernel.dk> From: Pavel Begunkov Message-ID: <2527d712-bc8b-7393-f4c0-3035dd525b1e@gmail.com> Date: Tue, 24 Aug 2021 10:48:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <59494bda-f804-4185-dd7d-4827b14bae61@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 8/23/21 8:40 PM, Jens Axboe wrote: > On 8/23/21 1:13 PM, Josh Triplett wrote: >> On Sat, Aug 21, 2021 at 08:18:12PM -0600, Jens Axboe wrote: >>> On 8/21/21 9:52 AM, Pavel Begunkov wrote: >>>> Add an optional feature to open/accept directly into io_uring's fixed >>>> file table bypassing the normal file table. Same behaviour if as the >>>> snippet below, but in one operation: >>>> >>>> sqe = prep_[open,accept](...); >>>> cqe = submit_and_wait(sqe); >>>> io_uring_register_files_update(uring_idx, (fd = cqe->res)); >>>> close((fd = cqe->res)); >>>> >>>> The idea in pretty old, and was brough up and implemented a year ago >>>> by Josh Triplett, though haven't sought the light for some reasons. >>>> >>>> The behaviour is controlled by setting sqe->file_index, where 0 implies >>>> the old behaviour. If non-zero value is specified, then it will behave >>>> as described and place the file into a fixed file slot >>>> sqe->file_index - 1. A file table should be already created, the slot >>>> should be valid and empty, otherwise the operation will fail. >>>> >>>> we can't use IOSQE_FIXED_FILE to switch between modes, because accept >>>> takes a file, and it already uses the flag with a different meaning. >>>> >>>> since RFC: >>>> - added attribution >>>> - updated descriptions >>>> - rebased >>>> >>>> since v1: >>>> - EBADF if slot is already used (Josh Triplett) >>>> - alias index with splice_fd_in (Josh Triplett) >>>> - fix a bound check bug >>> >>> With the prep series, this looks good to me now. Josh, what do you >>> think? >> >> I would still like to see this using a union with the `nofile` field in >> io_open and io_accept, rather than overloading the 16-bit buf_index >> field. That would avoid truncating to 16 bits, and make less work for >> expansion to more than 16 bits of fixed file indexes. >> >> (I'd also like that to actually use a union, rather than overloading the >> meaning of buf_index/nofile.) > > Agree, and in fact there's room in the open and accept command parts, so > we can just make it a separate entry there instead of using ->buf_index. > Then just pass in the index to io_install_fixed_file() instead of having > it pull it from req->buf_index. That's internal details, can be expanded at wish in the future, if we'd ever need larger tables. ->buf_index already holds indexes to different resources just fine. Aliasing with nofile would rather be ugly, so the only option, as you mentioned, is to grab some space from open/accept structs, but don't see why we'd want it when there is a more convenient alternative. >> I personally still feel that using non-zero to signify index-plus-one is >> both error-prone and not as future-compatible. I think we could do >> better with no additional overhead. But I think the final call on that >> interface is up to you, Jens. Do you think it'd be worth spending a flag >> bit or using a different opcode, to get a cleaner interface? If you >> don't, then I'd be fine with seeing this go in with just the io_open and >> io_accept change. > > I'd be inclined to go the extra opcode route instead, as the flag only > really would make sense to requests that instantiate file descriptors. > For this particular case, we'd need 3 new opcodes for > openat/openat2/accept, which is probably a worthwhile expenditure. > > Pavel, what do you think? Switch to using a different opcode for the new > requests, and just grab some space in io_open and io_accept for the fd > and pass it in to install. I don't get it, why it's even called hackish? How that's anyhow better? To me the feature looks like a natural extension to the operations, just like a read can be tuned with flags, so and creating new opcodes seems a bit ugly, unnecessary taking space from opcodes and adding duplication (even if both versions call the same handler). First, why it's not future-compatible? It's a serious argument, but I don't see where it came from. Do I miss something? It's u32 now, and so will easily cover all indexes. SQE fields should always be zeroed, that's a rule, liburing follows it, and there would have been already lots of problems for users not honoring it. And there will be a helper hiding all the index conversions for convenience. void io_uring_prep_open_direct(sqe, index, ...) { io_uring_prep_open(sqe, ...); sqe->file_index = index + 1; } -- Pavel Begunkov