[PATCH RFC] nvme: rewrite discard support

[Christoph Hellwig]

On Mon, Mar 21, 2016 at 03:51:39PM +0000, Keith Busch wrote:
> It looks like SCSI's special handling lead to what the code comments
> describe as a "horrible hack", so that's not convincing this is a good
> example to follow.

Nah, the "horrible hack" is adding a payload to the request.  We went
over and over this and everyone but Kent agrees it's the least horrible
option to handle discards in generic code.  NVMe side steps this a bit
by not trying to handle this in common code, but that only works as
long as it's a single tightly integrated driver, not for a layer
architecture like SCSI, or what NVMe is increasingly moving to.