[RFC PATCH] nvme-pci: Bounce buffer for interleaved metadata

[Keith Busch]

On Wed, Feb 28, 2018 at 05:37:01PM +0100, Christoph Hellwig wrote:
> On Wed, Feb 28, 2018 at 09:35:11AM -0700, Keith Busch wrote:
> > Right, this RFC is just about enabling formats that don't subscribe to
> > the DIX format. It turns out some people believe those extended LBAs
> > are useful for something.
> > 
> > I still think this LBA format is not a good fit for this driver, but
> > I'd like to not push people to use out-of-tree or user space drivers
> > if there is a reasonable way to accommodate here. The driver's existing
> > NVMe IO passthrough makes this format reachable already, but there is
> > resistance to use the ioctl over more standard read/write paths.
> 
> For a good reason.  I think these formats are completely bogus for
> something pretending to be a block device, and your patch just shows
> how bogus they are.
> 
> What is the use case for this silly game?

Certainly not for DIF PI. At a high level, the use case is to store
block data and its metadata atomically rather than write them separately.
RAID journal software might be able to leverage a device like that.