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Petersen" , "roland@purestorage.com" , Hannes Reinecke , Christoph Hellwig , "Frederick.Knight@netapp.com" , "zach.brown@ni.com" , "osandov@fb.com" , "lsf-pc@lists.linux-foundation.org" , "djwong@kernel.org" , "josef@toxicpanda.com" , "clm@fb.com" , "dsterba@suse.com" , "tytso@mit.edu" , "jack@suse.com" , Kanchan Joshi Subject: Re: [RFC PATCH 3/3] nvme: add the "debug" host driver Thread-Topic: [RFC PATCH 3/3] nvme: add the "debug" host driver Thread-Index: AQHYF5pGTuc0vK6aW0WDOYv4vbM4lKx/5pmAgAIScYCAABSnAIAAMdEAgAB7aoCAADa8gIAAGRyA Date: Fri, 4 Feb 2022 07:58:25 +0000 Message-ID: <9d5d0b50-2936-eac3-12d3-a309389e03bf@nvidia.com> References: <20220201102122.4okwj2gipjbvuyux@mpHalley-2> <270f30df-f14c-b9e4-253f-bff047d32ff0@nvidia.com> <20220203153843.szbd4n65ru4fx5hx@garbanzo> <20220203165238.GA142129@dhcp-10-100-145-180.wdc.com> <20220203195155.GB249665@bgt-140510-bm01> <863d85e3-9a93-4d8c-cf04-88090eb4cc02@nvidia.com> <2bbed027-b9a1-e5db-3a3d-90c40af49e09@opensource.wdc.com> In-Reply-To: <2bbed027-b9a1-e5db-3a3d-90c40af49e09@opensource.wdc.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mozilla/5.0 (X11; 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Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-MIME-Autoconverted: from base64 to 8bit by lists01.pubmisc.prod.ext.phx2.redhat.com id 2147wXMq001931 X-loop: dm-devel@redhat.com X-Mailman-Approved-At: Fri, 04 Feb 2022 04:41:43 -0500 Cc: Bart, "djwong@kernel.org" , "linux-nvme@lists.infradead.org" , "clm@fb.com" , "dm-devel@redhat.com" , Manzanares , "osandov@fb.com" , =?utf-8?B?SmF2aWVyIEdvbnrDoWxleg==?= , Assche , "linux-scsi@vger.kernel.org" , Christoph Hellwig , "roland@purestorage.com" , "zach.brown@ni.com" , "dsterba@suse.com" , "msnitzer@redhat.com >> msnitzer@redhat.com" , "josef@toxicpanda.com" , "linux-block@vger.kernel.org" , Mikulas Patocka , Keith Busch , "Frederick.Knight@netapp.com" , Jens Axboe , "tytso@mit.edu" , Kanchan Joshi , "martin.petersen@oracle.com >> Martin K. Petersen" , Luis Chamberlain , Adam, "jack@suse.com" , linux-fsdevel , "lsf-pc@lists.linux-foundation.org" Subject: Re: [dm-devel] [RFC PATCH 3/3] nvme: add the "debug" host driver X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On 2/3/22 22:28, Damien Le Moal wrote: > On 2/4/22 12:12, Chaitanya Kulkarni wrote: >> >>>>> One can instantiate scsi devices with qemu by using fake scsi devices, >>>>> but one can also just use scsi_debug to do the same. I see both efforts >>>>> as desirable, so long as someone mantains this. >>>>> >> >> Why do you think both efforts are desirable ? > > When testing code using the functionality, it is far easier to get said > functionality doing a simple "modprobe" rather than having to setup a > VM. C.f. running blktests or fstests. > agree on simplicity but then why do we have QEMU implementations for the NVMe features (e.g. ZNS, NVMe Simple Copy) ? we can just build memoery backed NVMeOF test target for NVMe controller features. Also, recognizing the simplicity I proposed initially NVMe ZNS fabrics based emulation over QEMU (I think I still have initial state machine implementation code for ZNS somewhere), those were "nacked" for the right reason, since we've decided go with QEMU and use that as a primary platform for testing, so I failed to understand what has changed.. since given that QEMU already supports NVMe simple copy ... > So personally, I also think it would be great to have a kernel-based > emulation of copy offload. And that should be very easy to implement > with the fabric code. Then loopback onto a nullblk device and you get a > quick and easy to setup copy-offload device that can even be of the ZNS > variant if you want since nullblk supports zones. > One can do that with creating null_blk based NVMeOF target namespace, no need to emulate simple copy memory backed code in the fabrics with nvme-loop.. it is as simple as inserting module and configuring ns with nvmetcli once we have finalized the solution for copy offload. If you remember, I already have patches for that... >> >> NVMe ZNS QEMU implementation proved to be perfect and works just >> fine for testing, copy offload is not an exception. >> >>>>> For instance, blktests uses scsi_debug for simplicity. >>>>> >>>>> In the end you decide what you want to use. >>>> >>>> Can we use the nvme-loop target instead? >>> >>> I am advocating for this approach as well. It presentas a virtual nvme >>> controller already. >>> >> >> It does that assuming underlying block device such as null_blk or >> QEMU implementation supports required features not to bloat the the >> NVMeOF target. >> >> -ck >> -ck -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel