From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=1.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,SPF_SOFTFAIL autolearn=no autolearn_force=no version=3.4.6 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1D5AC433EF for ; Fri, 11 Mar 2022 07:01:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346894AbiCKHC6 (ORCPT ); Fri, 11 Mar 2022 02:02:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346905AbiCKHC5 (ORCPT ); Fri, 11 Mar 2022 02:02:57 -0500 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64D6A1AC2AB; Thu, 10 Mar 2022 23:01:55 -0800 (PST) Received: by verein.lst.de (Postfix, from userid 2407) id 1BBA868BEB; Fri, 11 Mar 2022 08:01:49 +0100 (CET) Date: Fri, 11 Mar 2022 08:01:48 +0100 From: Christoph Hellwig To: Kanchan Joshi Cc: axboe@kernel.dk, hch@lst.de, kbusch@kernel.org, asml.silence@gmail.com, io-uring@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, sbates@raithlin.com, logang@deltatee.com, pankydev8@gmail.com, javier@javigon.com, mcgrof@kernel.org, a.manzanares@samsung.com, joshiiitr@gmail.com, anuj20.g@samsung.com Subject: Re: [PATCH 05/17] nvme: wire-up support for async-passthru on char-device. Message-ID: <20220311070148.GA17881@lst.de> References: <20220308152105.309618-1-joshi.k@samsung.com> <20220308152105.309618-6-joshi.k@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220308152105.309618-6-joshi.k@samsung.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Tue, Mar 08, 2022 at 08:50:53PM +0530, Kanchan Joshi wrote: > +/* > + * This overlays struct io_uring_cmd pdu. > + * Expect build errors if this grows larger than that. > + */ > +struct nvme_uring_cmd_pdu { > + u32 meta_len; > + union { > + struct bio *bio; > + struct request *req; > + }; > + void *meta; /* kernel-resident buffer */ > + void __user *meta_buffer; > +} __packed; Why is this marked __packed? In general I'd be much more happy if the meta elelements were a io_uring-level feature handled outside the driver and typesafe in struct io_uring_cmd, with just a normal private data pointer for the actual user, which would remove all the crazy casting. > +static void nvme_end_async_pt(struct request *req, blk_status_t err) > +{ > + struct io_uring_cmd *ioucmd = req->end_io_data; > + struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd); > + /* extract bio before reusing the same field for request */ > + struct bio *bio = pdu->bio; > + > + pdu->req = req; > + req->bio = bio; > + /* this takes care of setting up task-work */ > + io_uring_cmd_complete_in_task(ioucmd, nvme_pt_task_cb); This is a bit silly. First we defer the actual request I/O completion from the block layer to a different CPU or softirq and then we have another callback here. I think it would be much more useful if we could find a way to enhance blk_mq_complete_request so that it could directly complet in a given task. That would also be really nice for say normal synchronous direct I/O. > + if (ioucmd) { /* async dispatch */ > + if (cmd->common.opcode == nvme_cmd_write || > + cmd->common.opcode == nvme_cmd_read) { No we can't just check for specific commands in the passthrough handler. > + nvme_setup_uring_cmd_data(req, ioucmd, meta, meta_buffer, > + meta_len); > + blk_execute_rq_nowait(req, 0, nvme_end_async_pt); > + return 0; > + } else { > + /* support only read and write for now. */ > + ret = -EINVAL; > + goto out_meta; > + } Pleae always handle error in the first branch and don't bother with an else after a goto or return. > +static int nvme_ns_async_ioctl(struct nvme_ns *ns, struct io_uring_cmd *ioucmd) > +{ > + int ret; > + > + BUILD_BUG_ON(sizeof(struct nvme_uring_cmd_pdu) > sizeof(ioucmd->pdu)); > + > + switch (ioucmd->cmd_op) { > + case NVME_IOCTL_IO64_CMD: > + ret = nvme_user_cmd64(ns->ctrl, ns, NULL, ioucmd); > + break; > + default: > + ret = -ENOTTY; > + } > + > + if (ret >= 0) > + ret = -EIOCBQUEUED; That's a weird way to handle the returns. Just return -EIOCBQUEUED directly from the handler (which as said before should be split from the ioctl handler anyway).