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 101D6C61DFC for ; Sat, 21 Feb 2026 17:48:06 +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=XEDdppogwEP+4ij8Z1PfmxwFwT2NC0q+nxUKdPU0S8g=; b=dxYrgsOCZdFojRfjr6l1Cn2rGT n70iKas6imr+YsKphpf+G40SJNHLjQQykBO6wMT9hoBdlhMkOoO7cZiji9CvWSnCqBE1XcnojBdJs tAlD6Z2YAUpLlvknt/eGqmcH82P7nX1Ru0764NHuyN5nq2uIE65cZzvGrNDzzo3op/JPOSdaECZhn Symcb50VkDM0PoJ8yi4EnvVC4pkD8caCjRB3YvcViagDbdikxr7Ypiu8W3Z4y7nvrvyoaChr9hp6g F1Nr4ivbSKhuwh3xPIDP4l0VhmY7Em0HQsh3Dy7517EEAmLjcvjYbSbPuRSb1e2ahIX2Nwb3lHc/Z MUd+FDZQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vtr5I-0000000GDYx-0Mgr; Sat, 21 Feb 2026 17:48:04 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vtr5F-0000000GDYa-0bJf for linux-nvme@lists.infradead.org; Sat, 21 Feb 2026 17:48:02 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 0B91840A1F; Sat, 21 Feb 2026 17:48:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 937F9C4CEF7; Sat, 21 Feb 2026 17:47:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771696079; bh=4kSvkddoRLlf4Sl9dPi1cbg858c6h700l6Keq7+pJZE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lyhNHW29F+qYJ6yM4kxO0Dtu4K2ATWMw7JnFkeMoP5Ic1t8PdhhuJtV2Y+Dus2060 vVmaq/YSoyLzz1WB38ozkHHuGhgZenl9IHa9LEwYWQaM8AjPv8oBSqanAScb+MadEH UP7DWxkUFdASJ5aeyyIhCuFDE2Vgaz3g8TNlEOAGe1yv+rcsnYsGNE6Cl5MVdjPTyG z2JmOUT4x7cES1clgR961FQB1ci3CjDrAZuXamjZVVxbniVBeG+2xbTa2ExhLSej44 P/tGWYFVGqnOePLY4YQcpNoDeK6e1ijxCDOG/fClW398hmoqMslbAWkM+S2hpgGJPS 0nkyKP0bkJj/A== Date: Sat, 21 Feb 2026 12:47:58 -0500 From: Mike Snitzer To: Hannes Reinecke Cc: John Garry , lsf-pc@lists.linux-foundation.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org Subject: Re: [LSF/MM/BPF TOPIC] Native SCSI multipath support Message-ID: References: <69349b51-72c2-47f9-948f-f89843af62e4@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260221_094801_226575_522D43CB X-CRM114-Status: GOOD ( 32.20 ) 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 Mon, Feb 16, 2026 at 05:32:04PM +0100, Hannes Reinecke wrote: > On 2/14/26 10:42, John Garry wrote: > > On 13/02/2026 17:21, Hannes Reinecke wrote: > > > > At ALPSS 25 I presented a proposal for Native SCSI multipath > > > > support. Let's discuss this topic at LSFMM. > > > > > > > > The idea for this is that SCSI could natively support multipath, > > > > like how NVMe host driver does today. It is intended as an > > > > alternative to dm- multipath support. > > > > > > > > I have been working on the implementation and I plan to post > > > > patches in the next cycle. I am looking at a 3-stage approach: > > > > a. create a driver-agnostic multipath library, very heavily > > > > based on NVMe host multipath support. > > > > The library would support features such as path management, path > > > > selection/iopolicy, failover recovery, PR, delayed removal, > > > > gendisk management etc. > > > > b. switch NVMe over to use this library > > > > c. add native SCSI multipath support based on this common library > > > > > > > Go for it, John! > > > > > > I'd be very interested in that. > > > > cheers, in the meantime, I have some comments: > > > > - I need to test PRs for both NVMe and SCSI, any advice on that would be > > good. I don't think that blktests covers it. I did see Christoph mention > > a testsuite at: https://lore.kernel.org/linux-nvme/1438672271-11309-1- > > git-send-email-hch@lst.de/ - I can check that. > > > Well, you might have seen the discussion on the device-mapper list, where > stefanha is implementing generic PRs for dm-multipathing. > Or rather, trying to. We might need to revisit that and see what we > could be doing on the SCSI side. > Maybe we should be having a session about PRs at LSF? > > > - I am still not sure on whether we require a multipath version of sg. > > We can still have per-path sg. NVMe does have a multipath nvme-generic > > dev, but that just handles IOCTLs/uring cmd, and nothing like sg read/ > > write fops > > > 'sg' is primarily for testing 'raw' SCSI commands. (And dastardly complex to > boot). I really would keep it in it's current form, and not > try to mimick something with SCSI multipathing. > > > - I have not tried to detangle ALUA support from SCSI DH, so no ALUA > > support yet > > > Ouch. But that is the key point of the implementation; ALUA provides > _all_ the information required for multipathing, so how can you _not_ > have support for it? Exactly: no ALUA support makes, whatever this is, completely useless.