From: Sagi Grimberg <sagi@grimberg.me>
To: Logan Gunthorpe <logang@deltatee.com>,
Hannes Reinecke <hare@suse.de>,
linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc: Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
Jens Axboe <axboe@fb.com>,
Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
Max Gurtovoy <maxg@mellanox.com>,
Stephen Bates <sbates@raithlin.com>
Subject: Re: [PATCH v6 00/16] nvmet: add target passthru commands support
Date: Fri, 26 Jul 2019 15:21:14 -0700 [thread overview]
Message-ID: <175fa142-4815-ee48-82a4-18eb411db1ae@grimberg.me> (raw)
In-Reply-To: <8fd8813f-f8e1-2139-13bf-b0635a03bc30@deltatee.com>
>> How do you handle subsystem naming?
>> If you enable the 'passthru' device, the (nvmet) subsystem (and its
>> name) is already created. Yet the passthru device will have its own
>> internal subsystem naming, so if you're not extra careful you'll end up
>> with a nvmet subsystem which doesn't have any relationship with the
>> passthru subsystem, making addressing etc ... tricky.
>> Any thoughts about that?
>
> Well I can't say I have a great understanding of how multipath works, but...
Why is this related to multipath?
> I don't think it necessarily makes sense for the target subsynqn and the
> target's device nqn to be the same. It would be weird for a user to want
> to use the same device and a passed through device (through a loop) as
> part of the same subsystem. That being said, it's possible for the user
> to use the subsysnqn from the passed through device for the name of the
> subsys of the target. I tried this and it works except for the fact that
> the device I'm passing through doesn't set id->cmic.
I don't see why should the subsystem nqn should be the same name. Its
just like any other nvmet subsystem, just happens to have a nvme
controller in the backend (which it knows about). No reason to have
the same name IMO.
>> Similarly: how do you propose to handle multipath devices?
>> Any NVMe with several paths will be enabling NVMe multipathing
>> automatically, presenting you with a single multipathed namespace.
>> How will these devices be treated?
>
> Well passthru works on the controller level not on the namespace level.
> So it can't make use of the multipath handling on the target system.
Why? if nvmet is capable, why shouldn't we support it?
> The one case that I think makes sense to me, but I don't know how if we
> can handle, is if the user had a couple multipath enabled controllers
> with the same subsynqn
That is usually the case, there is no multipathing defined across NVM
subsystems (at least for now).
> and wanted to passthru all of them to another
> system and use multipath on the host with both controllers. This would
> require having multiple target subsystems with the same name which I
> don't think will work too well.
Don't understand why this is the case?
AFAICT, all nvmet needs to do is:
1. override cimc
2. allow allocating multiple controllers to the pt ctrl as long as the
hostnqn match.
3. answer all the ana stuff.
What else is missing?
>> Will the multipathed namespace be used for passthru?
>
> Nope.
>
> Honestly, I think the answer is if someone wants to use multipathed
> controllers they should use regular NVMe-of as it doesn't really mesh
> well with the passthru approach.
Maybe I'm missing something, but they should be orthogonal.. I know that
its sort of not real passthru, but we are exposing an nvme device across
a fabric, I think its reasonable to have some adjustments on top.
next prev parent reply other threads:[~2019-07-26 22:21 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-25 17:23 [PATCH v6 00/16] nvmet: add target passthru commands support Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 01/16] chardev: factor out cdev_lookup() helper Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 02/16] chardev: introduce cdev_get_by_path() Logan Gunthorpe
2019-07-25 17:40 ` Greg Kroah-Hartman
2019-07-25 17:53 ` Logan Gunthorpe
2019-07-25 17:58 ` Matthew Wilcox
2019-07-25 18:08 ` Logan Gunthorpe
2019-07-25 18:08 ` Greg Kroah-Hartman
2019-07-25 18:14 ` Logan Gunthorpe
2019-07-25 18:27 ` Greg Kroah-Hartman
2019-07-25 18:36 ` Logan Gunthorpe
2019-07-25 19:02 ` Sagi Grimberg
2019-07-25 19:34 ` Greg Kroah-Hartman
2019-07-25 19:37 ` Sagi Grimberg
2019-07-25 19:43 ` Greg Kroah-Hartman
2019-07-25 19:45 ` Sagi Grimberg
2019-07-25 19:43 ` Sagi Grimberg
2019-07-25 19:41 ` Logan Gunthorpe
2019-07-25 19:00 ` Matthew Wilcox
2019-07-25 19:05 ` Sagi Grimberg
2019-07-25 19:11 ` Matthew Wilcox
2019-07-25 19:24 ` Logan Gunthorpe
2019-07-25 19:26 ` Matthew Wilcox
2019-07-25 19:31 ` Logan Gunthorpe
2019-07-25 23:55 ` Al Viro
2019-07-26 4:29 ` Sagi Grimberg
2019-07-26 7:13 ` Greg Kroah-Hartman
2019-07-26 15:46 ` Logan Gunthorpe
2019-07-25 19:31 ` Sagi Grimberg
2019-07-25 18:10 ` Greg Kroah-Hartman
2019-07-25 18:16 ` Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 03/16] chardev: export cdev_put() Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 04/16] nvme-core: introduce nvme_get_by_path() Logan Gunthorpe
2019-07-25 17:50 ` Matthew Wilcox
2019-07-25 17:54 ` Logan Gunthorpe
2019-07-25 19:58 ` Keith Busch
2019-07-25 20:12 ` Sagi Grimberg
2019-07-25 20:28 ` Logan Gunthorpe
2019-07-25 20:31 ` Keith Busch
2019-07-25 20:37 ` Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 05/16] nvme-core: export existing ctrl and ns interfaces Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 06/16] nvmet: add return value to nvmet_add_async_event() Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 07/16] nvmet: make nvmet_copy_ns_identifier() non-static Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 08/16] nvmet-passthru: update KConfig with config passthru option Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 09/16] nvmet-passthru: add passthru code to process commands Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 10/16] nvmet-passthru: add enable/disable helpers Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 11/16] nvmet-core: allow one host per passthru-ctrl Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 12/16] nvmet-core: don't check the data len for pt-ctrl Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 13/16] nvmet-configfs: introduce passthru configfs interface Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 14/16] block: don't check blk_rq_is_passthrough() in blk_do_io_stat() Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 15/16] block: call blk_account_io_start() in blk_execute_rq_nowait() Logan Gunthorpe
2019-07-25 17:23 ` [PATCH v6 16/16] nvmet-passthru: support block accounting Logan Gunthorpe
2019-07-26 6:23 ` [PATCH v6 00/16] nvmet: add target passthru commands support Hannes Reinecke
2019-07-26 17:07 ` Logan Gunthorpe
2019-07-26 22:21 ` Sagi Grimberg [this message]
2019-07-26 22:37 ` Logan Gunthorpe
2019-07-26 23:13 ` Sagi Grimberg
2019-07-27 0:09 ` Logan Gunthorpe
2019-07-27 0:50 ` Stephen Bates
2019-07-29 16:15 ` Sagi Grimberg
2019-07-29 16:17 ` Logan Gunthorpe
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