[PATCH] nvme-cli: add support for directive command

[kwan.huen@samsung.com (Kwan (Hingkwan) Huen)]

> From: Keith Busch [mailto:keith.busch at intel.com]
> Sent: Friday, August 11, 2017 10:03 AM
> To: Kwan (Hingkwan) Huen <kwan.huen at samsung.com>
> Cc: linux-nvme at lists.infradead.org; axboe at kernel.dk; Changho Choi
> <changho.c at samsung.com>; Vijay Balakrishnan <vijay.bala at samsung.com>
> Subject: Re: [PATCH] nvme-cli: add support for directive command
> 
> On Thu, Aug 10, 2017@07:54:09PM -0700, kwan.huen@samsung.com wrote:
> > Directive is a feature introduced in NVMe v1.3 that allows host and
> > NVM subsystem or controller information exchange, namely data lifetime
> > hint for example. Information is transmitted using the Directive Send
> > and Directive Receive commands.
> >
> > This patch set allows control of the directive resources of a
> > directive-enabled nvme device.
> 
> The patches themselves look great, but I didn't realize this was a feature user-
> space should be accessing. Providing this could mess up the streams the kernel
> believes are set up, right?

Hi Keith,
Sorry for late! 
That's a valid concern. But the only thing I can see, which potentially cause 
problem, is the stream directive enable/disable. With kernel enables and 
manages the streams, if the tool can disable it, it'll cause IO error because the 
device no longer takes stream write commands. I think we can disable this 
directive enable/disable in this patch for now to avoid this problem, until 
we have a better way to coordinate this with the driver.
Besides that, I think it is still valuable for the tool that allows users 
to quickly check the directive functionalities and get status. In addition, the patch
also enables other features, e.g., users can allocate stream resources 
dedicated to namespace.
Regards,
kwan