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

[Keith Busch]

On Fri, Feb 04, 2022 at 03:15:02PM +0100, Hannes Reinecke wrote:
> On 2/4/22 10:58, Chaitanya Kulkarni wrote:
> 
> > and if that is the case why we don't have ZNS NVMeOF target
> > memory backed emulation ? Isn't that a bigger and more
> > complicated feature than Simple Copy where controller states
> > are involved with AENs ?
> > 
> > ZNS kernel code testing is also done on QEMU, I've also fixed
> > bugs in the ZNS kernel code which are discovered on QEMU and I've not
> > seen any issues with that. Given that simple copy feature is way smaller
> > than ZNS it will less likely to suffer from slowness and etc (listed
> > above) in QEMU.
> > 
> > my point is if we allow one, we will be opening floodgates and we need
> > to be careful not to bloat the code unless it is _absolutely
> > necessary_ which I don't think it is based on the simple copy
> > specification.
> > 
> 
> I do have a slightly different view on the nvme target code; it should
> provide the necessary means to test the nvme host code.
> And simple copy is on of these features, especially as it will operate as an
> exploiter of the new functionality.

The threshold to determine if the in-kernel fabrics target ought to
implement a feature should be if it's useful in a production.

Are users interested in copying data without using fabric bandwidth?
Yes.

Does anyone want a mocked up ZNS that has all the contraints and none of
the benefits? No.