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=-7.7 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,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A62F9C433DB for ; Thu, 28 Jan 2021 17:17:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FFEB64DA1 for ; Thu, 28 Jan 2021 17:17:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232673AbhA1RRG (ORCPT ); Thu, 28 Jan 2021 12:17:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232237AbhA1ROj (ORCPT ); Thu, 28 Jan 2021 12:14:39 -0500 Received: from mail-wm1-x331.google.com (mail-wm1-x331.google.com [IPv6:2a00:1450:4864:20::331]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98780C06178A; Thu, 28 Jan 2021 09:13:55 -0800 (PST) Received: by mail-wm1-x331.google.com with SMTP id j18so4920615wmi.3; Thu, 28 Jan 2021 09:13:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=7SlUdwnPEQ27NCqhpgbYeyZWdUr/hbFxWqlJ+t74Kk8=; b=ZC610tgYYf3cXDd+K9835SRwKWS9h9WUHGCpEUZ6linSddg1wSPgVUjUNMN6mpS1Xm c4RrThuc6ArJUvlpnCsDOLiTLXxwP4gT29yqtbht4QP3gi5mE1lN6atmRBYG5NOiIKd1 UhbGMFx8WThSp9iqxgoxo/aLM4qGLH8FwsrhUGC7qHZZCD6xm1tQMuyj2HAydcxCz3uI zskopGXRLz1XCgVbA2eQnIP2B5tmj8BCKRe8kXTgUz3M5QuORrsxvnYibguygGOosJF4 8a6/v6PxOY926xVk3IVjtF+tjo+vcHysccUiuGX/6NIZCEvi7yotZrDMKGZbLUbe4IFg I9PA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7SlUdwnPEQ27NCqhpgbYeyZWdUr/hbFxWqlJ+t74Kk8=; b=FDUgEWyyvfydp0FdVc+3MX2rp5wGM+BOfQLAvVfTI/t3ulYktL0RwFaOklv8m4dokA ldIRNngS2Jq86oi3jJS9aEt0Zi2r/x+NzvwTv4DyDuq5azv1UMPzYP+QJunWuagjn2zt b5oynm1l74gvSvX1/7cf3DXwf9d9e0LsRwBXnEFtAVN3AR4AwfSf4D8wEdWIXB5h1Ti5 SAxWn6chQIH4ANaHd2sUaQkDYVsElxHgUgsxkmjqXxDmYz2fnoBXrkZl0ICz/sm0T7aX folWqigcFSRgNmdgm/6bbduEzT5UhEW8sE4AbRpaMC32tppaUfLz812vQ0IPQfKgVfW9 V/qw== X-Gm-Message-State: AOAM533VN/m670ub4v+5GrO9w6OAkhKLdCeJSpMKkm/JA5Bi2syhhrTc p+zqCZZ3+J4ZS/pRPDytFrQNC5adui4STnY8/JUvnGiIyIY= X-Google-Smtp-Source: ABdhPJxXfXzFAr81U6woMH6ZlFCnx3rqdBDQvkZZfBp9Z6iPwsJ146GcYd//CXg+XfSzjLO8DPOg85PKnI4yVDcLSOo= X-Received: by 2002:a1c:5f54:: with SMTP id t81mr233174wmb.25.1611854034115; Thu, 28 Jan 2021 09:13:54 -0800 (PST) MIME-Version: 1.0 References: <20210127150029.13766-1-joshi.k@samsung.com> <489691ce-3b1e-30ce-9f72-d32389e33901@gmail.com> <2d37d0ca-5853-4bb6-1582-551b9044040c@kernel.dk> In-Reply-To: <2d37d0ca-5853-4bb6-1582-551b9044040c@kernel.dk> From: Kanchan Joshi Date: Thu, 28 Jan 2021 22:43:26 +0530 Message-ID: Subject: Re: [RFC PATCH 0/4] Asynchronous passthrough ioctl To: Jens Axboe Cc: Pavel Begunkov , Kanchan Joshi , Keith Busch , Christoph Hellwig , sagi@grimberg.me, linux-nvme@lists.infradead.org, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Javier Gonzalez , Nitesh Shetty , Selvakumar S Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Jan 28, 2021 at 8:08 PM Jens Axboe wrote: > > On 1/28/21 5:04 AM, Kanchan Joshi wrote: > > On Wed, Jan 27, 2021 at 9:32 PM Pavel Begunkov wrote: > >> > >> On 27/01/2021 15:42, Pavel Begunkov wrote: > >>> On 27/01/2021 15:00, Kanchan Joshi wrote: > >>>> This RFC patchset adds asynchronous ioctl capability for NVMe devices. > >>>> Purpose of RFC is to get the feedback and optimize the path. > >>>> > >>>> At the uppermost io-uring layer, a new opcode IORING_OP_IOCTL_PT is > >>>> presented to user-space applications. Like regular-ioctl, it takes > >>>> ioctl opcode and an optional argument (ioctl-specific input/output > >>>> parameter). Unlike regular-ioctl, it is made to skip the block-layer > >>>> and reach directly to the underlying driver (nvme in the case of this > >>>> patchset). This path between io-uring and nvme is via a newly > >>>> introduced block-device operation "async_ioctl". This operation > >>>> expects io-uring to supply a callback function which can be used to > >>>> report completion at later stage. > >>>> > >>>> For a regular ioctl, NVMe driver submits the command to the device and > >>>> the submitter (task) is made to wait until completion arrives. For > >>>> async-ioctl, completion is decoupled from submission. Submitter goes > >>>> back to its business without waiting for nvme-completion. When > >>>> nvme-completion arrives, it informs io-uring via the registered > >>>> completion-handler. But some ioctls may require updating certain > >>>> ioctl-specific fields which can be accessed only in context of the > >>>> submitter task. For that reason, NVMe driver uses task-work infra for > >>>> that ioctl-specific update. Since task-work is not exported, it cannot > >>>> be referenced when nvme is compiled as a module. Therefore, one of the > >>>> patch exports task-work API. > >>>> > >>>> Here goes example of usage (pseudo-code). > >>>> Actual nvme-cli source, modified to issue all ioctls via this opcode > >>>> is present at- > >>>> https://github.com/joshkan/nvme-cli/commit/a008a733f24ab5593e7874cfbc69ee04e88068c5 > >>> > >>> see https://git.kernel.dk/cgit/linux-block/log/?h=io_uring-fops > >>> > >>> Looks like good time to bring that branch/discussion back > >> > >> a bit more context: > >> https://github.com/axboe/liburing/issues/270 > > > > Thanks, it looked good. It seems key differences (compared to > > uring-patch that I posted) are - > > 1. using file-operation instead of block-dev operation. > > Right, it's meant to span wider than just block devices. > > > 2. repurpose the sqe memory for ioctl-cmd. If an application does > > ioctl with <=40 bytes of cmd, it does not have to allocate ioctl-cmd. > > That's nifty. We still need to support passing larger-cmd (e.g. > > nvme-passthru ioctl takes 72 bytes) but that shouldn't get too > > difficult I suppose. > > It's actually 48 bytes in the as-posted version, and I've bumped it to > 56 bytes in the latest branch. So not quite enough for everything, > nothing ever will be, but should work for a lot of cases without > requiring per-command allocations just for the actual command. Agreed. But if I got it right, you are open to support both in-the-sqe command (<= 56 bytes) and out-of-sqe command (> 56 bytes) with this interface. Driver processing the ioctl can fetch the cmd from user-space in one case (as it does now), and skips in another. > > And for some ioctls, driver may still need to use task-work to update > > the user-space pointers (embedded in uring/ioctl cmd) during > > completion. > > > > @Jens - will it be fine if I start looking at plumbing nvme-part of > > this series on top of your work? > > Sure, go ahead. Just beware that things are still changing, so you might > have to adapt it a few times. It's still early days, but I do think > that's the way forward in providing controlled access to what is > basically async ioctls. Sounds good, I will start with the latest branch that you posted. Thanks. -- Kanchan