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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 128B4C433EF for ; Wed, 13 Jul 2022 13:30:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229918AbiGMNad (ORCPT ); Wed, 13 Jul 2022 09:30:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230014AbiGMNac (ORCPT ); Wed, 13 Jul 2022 09:30:32 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3664EAE58; Wed, 13 Jul 2022 06:30:30 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 9D7C720169; Wed, 13 Jul 2022 13:30:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1657719029; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eoqwuQBJmvT5vHyOX/uOhNJwWoGP1SXF2teBGiNr6ns=; b=BPFcgJUSLUf4wxDFT3zRkBPOIHvFGbPlijv/rLKnEXFhJBNFaUFz92XUDgnvFzbljsy0FZ vpiPxDxBwqiiwdeeOsHYPVn6q6ErZXhaoVxTLqMR4Qh8V97FbS65fZ+1i6y2PeNobV9bvv JpXl6Ubt2V7Q75L54rvsjuID31K+u2g= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1657719029; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eoqwuQBJmvT5vHyOX/uOhNJwWoGP1SXF2teBGiNr6ns=; b=COi6ZpXj5VxYXo+ClQsS0BsYESRnBB0SACjD44tSm+f8R6ECgsZcKZVv5T0AqNHoA3tBtw 5xZ3+hbgmlBGnSAw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 82ED213754; Wed, 13 Jul 2022 13:30:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id yqGvH/XIzmKDRgAAMHmgww (envelope-from ); Wed, 13 Jul 2022 13:30:29 +0000 Message-ID: <04b475f6-506f-188b-d104-b27e9dffc1b8@suse.de> Date: Wed, 13 Jul 2022 15:30:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands Content-Language: en-US To: Sagi Grimberg , Christoph Hellwig Cc: 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 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> <20220713101235.GA27815@lst.de> <772b461a-bc43-c229-906d-0e280091e17f@grimberg.me> <96f47d9b-fbfc-80da-4c38-f46986f14a43@suse.de> <7c7a093c-4103-b67d-c145-9d84aaae835e@grimberg.me> From: Hannes Reinecke In-Reply-To: <7c7a093c-4103-b67d-c145-9d84aaae835e@grimberg.me> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 7/13/22 14:43, Sagi Grimberg wrote: > > > On 7/13/22 14:49, Hannes Reinecke wrote: >> On 7/13/22 13:00, 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. >>> >>> I view uring passthru somewhat as a different thing than sending SG_IO >>> ioctls to dm-mpath. But it can be argued otherwise. >>> >>> BTW, the only consumer of it that I'm aware of commented that he >>> expects dm-mpath to retry SG_IO when dm-mpath retry for SG_IO submission >>> was attempted (https://www.spinics.net/lists/dm-devel/msg46924.html). >>> >>>  From Paolo: >>> "The problem is that userspace does not have a way to direct the >>> command to a different path in the resubmission. It may not even have >>> permission to issue DM_TABLE_STATUS, or to access the /dev nodes for >>> the underlying paths, so without Martin's patches SG_IO on dm-mpath >>> is basically unreliable by design." >>> >>> I didn't manage to track down any followup after that email though... >>> >> I did; 'twas me who was involved in the initial customer issue leading >> up to that. >> >> Amongst all the other issue we've found the prime problem with SG_IO >> is that it needs to be directed to the 'active' path. >> For the device-mapper has a distinct callout (dm_prepare_ioctl), which >> essentially returns the current active path device. And then the >> device-mapper core issues the command on that active path. >> >> All nice and good, _unless_ that command triggers an error. >> Normally it'd be intercepted by the dm-multipath end_io handler, and >> would set the path to offline. >> But as ioctls do not use the normal I/O path the end_io handler is >> never called, and further SG_IO calls are happily routed down the >> failed path. >> >> And the customer had to use SG_IO (or, in qemu-speak, LUN passthrough) >> as his application/filesystem makes heavy use of persistent reservations. > > How did this conclude Hannes? It didn't. The proposed interface got rejected, and now we need to come up with an alternative solution. Which we haven't found yet. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer