[dm-devel] [RFC PATCH 3/3] nvme: add the "debug" host driver

[Damien Le Moal]

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.

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.

> 
> 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
> 
> 


-- 
Damien Le Moal
Western Digital Research