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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4A53EC43334 for ; Wed, 13 Jul 2022 10:13:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=FD8BDK4X+ZzmmlH6OtSYYvImmuY1w3N7LKxwjYpBnvQ=; b=AQkOcqm8yD5/rmcO40cYN2Nefl XVlSx10ni2a1FRFnfnfn0VoY3YesWNvAHvKpUwHCADDukQdlBwM7e9goviK1hb/UGM/FxH++QeHxA /mvXDvo2LaPpHJ4UxR5sUaI+FIQROoJ8o4dI3bNi8VodORc4Rdnr5s74XkWn5Y7c/JEBg9ttPugd2 v0iCSEEO7tPB55TX4y76a8Vda0H2hTim3Q77XnkGm5Lc89N+ntWZozKx7xfW8RM2fhyYRcup/XmhU 0cy4Ra4FkwPWIgKjV27+LeD692fvp+RGjXDoGYtdSdpsMzTa7Q+RWIJWi72EIOtgDaKLbi4h35hbE nVpXY/Dg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oBZMZ-002cxv-S3; Wed, 13 Jul 2022 10:12:59 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oBZMW-002co3-QA for linux-nvme@lists.infradead.org; Wed, 13 Jul 2022 10:12:58 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7CBD167373; Wed, 13 Jul 2022 12:12:35 +0200 (CEST) Date: Wed, 13 Jul 2022 12:12:35 +0200 From: Christoph Hellwig To: Sagi Grimberg Cc: Christoph Hellwig , Kanchan Joshi , kbusch@kernel.org, axboe@kernel.dk, io-uring@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, asml.silence@gmail.com, joshiiitr@gmail.com, anuj20.g@samsung.com, gost.dev@samsung.com Subject: Re: [PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands Message-ID: <20220713101235.GA27815@lst.de> References: <20220711110155.649153-1-joshi.k@samsung.com> <20220711110155.649153-5-joshi.k@samsung.com> <20220712065250.GA6574@lst.de> <436c8875-5a99-4328-80ac-6a5aef7f16f4@grimberg.me> <20220713053633.GA13135@lst.de> <24f0a3e6-aa53-8c69-71b7-d66289a63eae@grimberg.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24f0a3e6-aa53-8c69-71b7-d66289a63eae@grimberg.me> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220713_031257_033444_63BDF749 X-CRM114-Status: GOOD ( 15.97 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Wed, Jul 13, 2022 at 11:04:31AM +0300, Sagi Grimberg wrote: > Maybe the solution is to just not expose a /dev/ng for the mpath device > node, but only for bottom namespaces. Then it would be completely > equivalent to scsi-generic devices. > > It just creates an unexpected mix of semantics of best-effort > multipathing with just path selection, but no requeue/failover... Which is exactly the same semanics as SG_IO on the dm-mpath nodes. > If the user needs to do the retry, discover and understand namespace > paths, ANA states, controller states, etc. Why does the user need a > mpath chardev at all? The user needs to do that for all kinds of other resons anyway, as we don't do any retries for passthrough at all.