Re: [PATCH 5/5] nvme: support for zoned namespaces

["Matias Bjørling" <mb@lightnvm.io>]

On 16/06/2020 14.24, Javier González wrote:
> On 16.06.2020 14:06, Matias Bjørling wrote:
>> On 16/06/2020 14.00, Javier González wrote:
>>> On 16.06.2020 13:18, Matias Bjørling wrote:
>>>> On 16/06/2020 12.41, Javier González wrote:
>>>>> On 16.06.2020 08:34, Keith Busch wrote:
>>>>>> Add support for NVM Express Zoned Namespaces (ZNS) Command Set 
>>>>>> defined
>>>>>> in NVM Express TP4053. Zoned namespaces are discovered based on 
>>>>>> their
>>>>>> Command Set Identifier reported in the namespaces Namespace
>>>>>> Identification Descriptor list. A successfully discovered Zoned
>>>>>> Namespace will be registered with the block layer as a host managed
>>>>>> zoned block device with Zone Append command support. A namespace 
>>>>>> that
>>>>>> does not support append is not supported by the driver.
>>>>>
>>>>> Why are we enforcing the append command? Append is optional on the
>>>>> current ZNS specification, so we should not make this mandatory in 
>>>>> the
>>>>> implementation. See specifics below.
>>>
>>>>
>>>> There is already general support in the kernel for the zone append 
>>>> command. Feel free to submit patches to emulate the support. It is 
>>>> outside the scope of this patchset.
>>>>
>>>
>>> It is fine that the kernel supports append, but the ZNS specification
>>> does not impose the implementation for append, so the driver should not
>>> do that either.
>>>
>>> ZNS SSDs that choose to leave append as a non-implemented optional
>>> command should not rely on emulated SW support, specially when
>>> traditional writes work very fine for a large part of current ZNS use
>>> cases.
>>>
>>> Please, remove this virtual constraint.
>>
>> The Zone Append command is mandatory for zoned block devices. Please 
>> see https://lwn.net/Articles/818709/ for the background.
>
> I do not see anywhere in the block layer that append is mandatory for
> zoned devices. Append is emulated on ZBC, but beyond that there is no
> mandatory bits. Please explain.
>
>> Please submitpatches if you want to have support for ZNS devices that
>> does not implement the Zone Append command. It is outside the scope
>> of this patchset.
>
> That we will.
>
Thanks, appreciate it.

Best, Matias