From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A89AC2F39CE; Sat, 21 Feb 2026 17:48:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771696080; cv=none; b=eoMuKcj8zcvuakww2uIP4NVfBj3GToPm8sw/R8khHFbhQUObIZUFXszh09IYtJysLk5JNDD5CAPq/qYO3e3+RnuPgsYJDRAKYUevLinRLVVt2C197GCPzN8KRpLtwHUEQsc+Q8M7peomsAa/8PeZchJnF6UD8/R9TaJVQBYGOyI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771696080; c=relaxed/simple; bh=4kSvkddoRLlf4Sl9dPi1cbg858c6h700l6Keq7+pJZE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GiKPc5z/IbSk5DmVCczu/RmPQ83n33BHldUqL34uMkU6ubyGIILpTNaFRy+jMP94SQzCWHdq54/SN+AOtuwKpRLnlb5805GTgS3LtCakHyv7ajoQkTcMQRGZbN0vCLv3v9Q7Mrd96DVGOT6TfXkn3Da0RV9rQS8X/EHIzFTRQJo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lyhNHW29; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lyhNHW29" 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> Precedence: bulk X-Mailing-List: linux-scsi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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.