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([2a01:4a0:2e:ffff:ffff:ffff:ffff:ffff]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48722d38a5fsm19972075e9.12.2026.03.26.03.17.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Mar 2026 03:17:59 -0700 (PDT) Message-ID: <554f791d-17c2-48ab-8014-1ef62ba5b85d@suse.com> Date: Thu, 26 Mar 2026 11:17:58 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/13] scsi: Core ALUA driver To: Benjamin Marzinski , John Garry Cc: martin.petersen@oracle.com, james.bottomley@hansenpartnership.com, jmeneghi@redhat.com, linux-scsi@vger.kernel.org, michael.christie@oracle.com, snitzer@kernel.org, dm-devel@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260317120703.3702387-1-john.g.garry@oracle.com> <10aab639-2fe8-47b7-b821-12d21b6af874@oracle.com> <43ca92bc-af38-4833-841c-421997ed90fe@oracle.com> Content-Language: en-US From: Hannes Reinecke In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/24/26 14:58, Benjamin Marzinski wrote: > On Tue, Mar 24, 2026 at 10:57:20AM +0000, John Garry wrote: >> On 23/03/2026 19:45, Benjamin Marzinski wrote: >>>>> I don't >>>>> think the Native SCSI multipath code would need to actively interface >>>>> with the device handler code to support IMPLICIT ALUA. IIUC, looking at >>>>> sdev->access_state should be enough to pick the correct path. >>>> We also have the functionality from alua_check_sense() to consider. >>> But the multipath code won't call that directly. Right now, the scsi >>> device handler will, at least for every scsi device except ones using >>> the Native Multipath code. My point is that this would just work, except >>> that the Native Multipath code goes out of its way to break it, by >>> disabling device handlers, and I don't really see the point of disabling >>> something that every other scsi device, multipathed or not, has enabled. >>> It's not like leaving it enabled makes it any harder to move the >>> implicit ALUA support from the device handler to the generic scsi code, >>> if that's the goal, since the Native Multipath code doesn't care who is >>> issuing those rtpgs and updating the state. >>> >>> I guess this is more of a question for Hannes. Is the goal to turn off >>> automatic device handler attachment in general, and go back to making >>> dm-multipath attach device handlers to the scsi devices it is using? >> >> I'm not answering for Hannes, but I don't think that is the goal. >> >>> If >>> not, then I don't see any reason to have the Native Multipath code >>> disable it. >> >> It was just disabled it as we now had another method in the scsi core code >> to get ALUA info. >> >> My plan would be - based on this series - to not attach DH just when using >> native SCSI multipath for a device. >> >>> If it allowed device handlers to get attached, these two >>> developement efforts (native scsi multipath and refactoring the alua >>> support) could go on in parallel. >>> >>> Or am I missing something here? >> >> It just seems to be about this DH stuff is that there is bad history there >> and no more users are wanted. > > Just to be clear, if the idea was that the Native Multipath code > shouldn't use include/scsi/scsi_dh.h, I completely agree with that. But > I don't see why it can't make use of the results of the existing > implicit ALUA support, since IIUC it doesn't need the scsi_dh interface > to do that. That shouldn't interfere with any refactoring that people > want to do of how the scsi layer actually handles ALUA support. Again, > this is more for Hannes than you, John. > Oh, it's not that it technically cannot use it. It's just a design thingie: my idea for the native SCSI multipathing is that it should be _simple_. There really is not point (and, in fact, was one of the main motivators of this idea) to re-implement every nook and crannie from dm-multipathing. SCSI multipathing should only handle implicit ALUA, and leave every other functionality to dm-multipathing. And on the other side, I always found it completely irritating that one had to enable multipathing in order to get ALUA support (ie being able to figure out the ALUA state). The ALUA state is a property of the LUN, and the system has to react on that one. It really doesn't matter whether the system has multipathing enabled; if the LUN is in ALUA Standby state we cannot send I/O, full stop. And that's what we're trying to achieve here; move implicit alua support from SCSI DH into the SCSI core, and leave SCSI DH to handle explicit ALUA support. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.com +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich