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Re: [Qemu-devel] If Qemu support NVMe over Fabrics ?y

From: Paolo Bonzini
Subject: Re: [Qemu-devel] If Qemu support NVMe over Fabrics ?y
Date: Fri, 11 Jan 2019 17:07:26 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1

On 11/01/19 16:58, Stefan Hajnoczi wrote:
> On Fri, Jan 11, 2019 at 11:48:52AM +0100, Paolo Bonzini wrote:
>> On 11/01/19 06:46, Yang Zhong wrote:
>>> On Thu, Jan 10, 2019 at 10:36:37AM +0000, Stefan Hajnoczi wrote:
>>>> On Thu, Jan 10, 2019 at 04:37:53PM +0800, Yang Zhong wrote:
>>>>> Do you know if Qemu support NVMe over Fabrics(NVMe-oF)?
>>>>> https://nvmexpress.org/wp-content/uploads/NVMe_Over_Fabrics.pdf
>>>>> The Qemu has enabled RDMA in last year, and i am not sure if Qemu 
>>>>> should support NVME-oF. If Qemu support it, would you please share
>>>>> me the qemu related command or guides? thanks a lot!
>>>> QEMU supports many different storage configurations.  Can you be more
>>>> specific?
>>>> For example, if your host has NVMe-oF set up then you can give the NVMe
>>>> block devices to QEMU just like any other host block device (-drive
>>>> file=/dev/sdc,...).
>>>> But maybe you are thinking about other configurations, like exposing
>>>> NVMe-oF to the guest?
>>>   Thanks Stefan's comments. We only want Qemu as NVMe-oF initiator to
>>>   access remote target's resource.
>>>   I checked the block/nvme.c and hw/block/nvme.c code, which seems do
>>>   not support NVMe-oF . If i am wrong please correct me.
>>>   If Qemu support NVMe-oF initiator, please share me how to use it. 
>>>   If Qemu does not support it, please tell me if community has plan 
>>>   to implement it. thanks a lot!
>> QEMU's native NVMe driver only supports NVMe over PCI, but it should be
>> possible to extract common code if you want to add a native NVMe over
>> RDMA driver to QEMU.  There are currently no plans to add such a driver,
>> but it would certainly be a welcome addition.
> Before investing time in doing that, what is the goal?
> Is this for test and bring-up of NVMe-oF?  Or why does the guest need to
> know that the storage is NVMe-oF?
> As I mentioned before, if your host supports NVMe-oF you can simply give
> the block device to QEMU and let the guest access it via virtio-blk,
> virtio-scsi, NVMe, etc.

NVMe-OF is an RDMA protocol, basically a different transport for the
NVMe command set and queue abstraction.  It would allow QEMU to access
the device directly (similar to what block/nvme.c does for PCI using
VFIO) without going through the host kernel.  The guest would see the
device as virtio-blk/scsi, NVMe or anything else.


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