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Date:   Mon, 12 Dec 2022 16:49:19 +0200
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Subject: Re: [RFC PATCH 1/5] nvme-pci: add function nvme_submit_vf_cmd to
 issue admin commands for VF driver.
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To:     Christoph Hellwig <hch@lst.de>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, Lei Rao <lei.rao@intel.com>,
        kbusch@kernel.org, axboe@fb.com, kch@nvidia.com, sagi@grimberg.me,
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        shameerali.kolothum.thodi@huawei.com, kevin.tian@intel.com,
        mjrosato@linux.ibm.com, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, kvm@vger.kernel.org,
        eddie.dong@intel.com, yadong.li@intel.com, yi.l.liu@intel.com,
        Konrad.wilk@oracle.com, stephen@eideticom.com, hang.yuan@intel.com,
        Oren Duer <oren@nvidia.com>
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From:   Max Gurtovoy <mgurtovoy@nvidia.com>
In-Reply-To: <20221212075541.GC11162@lst.de>
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On 12/12/2022 9:55 AM, Christoph Hellwig wrote:
> On Sun, Dec 11, 2022 at 01:39:37PM +0200, Max Gurtovoy wrote:
>> 1. Need to define a concept of a "virtual subsystem". A primary controller
>> will be able to create a virtual subsystem. Inside this subsystem the
>> primary controller will be the master ("the controlling") of the migration
>> process. It will also be able to add secondary controllers to this virtual
>> subsystem and assign "virtual controller ID" to it.
>> something like:
>> - nvme virtual_subsys_create --dev=/dev/nvme1 --virtual_nqn="my_v_nqn_1"
>> --dev_vcid = 1
>> - nvme virtual_subsys_add --dev=/dev/nvme1 --virtual_nqn="my_v_nqn_1"
>> --secondary_dev=/dev/nvme2 --secondary_dev_vcid=20
> Yes. Note that there is a bit more state than just the NQN.  You also
> need at least a serial number, and also probably a different vendor
> ID (the PCI vendor ID that is also mirror in Identify Controller and
> the IEEE OUI), and new unique namespace identifier.

Yes for sure there is more bits we should consider.

I wanted to describe the high level.

I think that we can maybe say the when a secondary function is moved to 
a virtual subsystem its feature set of the virtual ctrl is narrowed to 
mandatory NVMe features set.
And we'll provide an API to set/extend it's feature set to a maximum of 
the feature set that the original ctrl of the secondary function had.
Then the sys admin will configure the virtual ctrl in both src/dst hosts.

The high level idea is to have a programmable way to set the features of 
a virtual controller inside a virtual subsystem that is also programmable.