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

[Adam Manzanares]

On Thu, Feb 03, 2022 at 03:57:55PM -0500, Mikulas Patocka wrote:
> 
> 
> On Thu, 3 Feb 2022, Luis Chamberlain wrote:
> 
> > On Thu, Feb 03, 2022 at 05:15:34PM +0100, Christoph Hellwig wrote:
> > > On Thu, Feb 03, 2022 at 08:06:33AM -0800, Luis Chamberlain wrote:
> > > > On Wed, Feb 02, 2022 at 06:01:13AM +0000, Adam Manzanares wrote:
> > > > > BTW I think having the target code be able to implement simple copy without 
> > > > > moving data over the fabric would be a great way of showing off the command.
> > > > 
> > > > Do you mean this should be implemented instead as a fabrics backend
> > > > instead because fabrics already instantiates and creates a virtual
> > > > nvme device? And so this would mean less code?
> > > 
> > > It would be a lot less code.  In fact I don't think we need any new code
> > > at all.  Just using nvme-loop on top of null_blk or brd should be all
> > > that is needed.
> > 
> > Mikulas,
> > 
> > That begs the question why add this instead of using null_blk with
> > nvme-loop?
> > 
> >   Luis
> 
> I think that nvme-debug (the patch 3) doesn't have to be added to the 
> kernel.
> 
> Nvme-debug was an old student project that was canceled. I used it because 
> it was very easy to add copy offload functionality to it - adding this 
> capability took just one function with 43 lines of code (nvme_debug_copy).
>

BTW Kanchan's group has looked at adding copy offload support to the target.
I'll let him respond on the timing of upstreaming, I'm under the assumption
that it is also a relatively small patch to the target code.

> I don't know if someone is interested in continuing the development of 
> nvme-debug. If yes, I can continue the development, if not, we can just 
> drop it.
> 
> Mikulas
>