[PATCH V2] nvme: report capacity 0 for non supported ZNS SSDs

[hch at lst.de]

On Mon, Nov 02, 2020 at 10:33:55AM -0800, Keith Busch wrote:
> I can see this going one of two ways:
> 
>  a) Set up the existing controller character device with a generic
>     disk-less request_queue to the IO queues accepting IO commands to
>     arbitrary NSIDs.
> 
>  b) Each namespace that can't be supported gets their own character
>     device.
> 
> I'm leaning toward option "a". While it doesn't create handles to unique
> namespaces, it has more resilience to potentially future changes. And I
> recall the target side had a potential use for that, too.

The problem with a) is that it can't be used to give users or groups
access to just one namespaces, so it causes a real access control
nightmare.  The problem with b) is that now applications will break
when we add support for new command sets or features.  I think

  c) Each namespace gets its own character device, period.

is the only sensible option.