From mboxrd@z Thu Jan 1 00:00:00 1970 From: keith.busch@intel.com (Keith Busch) Date: Wed, 28 Feb 2018 12:54:11 -0700 Subject: [RFC PATCH] nvme-pci: Bounce buffer for interleaved metadata In-Reply-To: <20180228163701.GA16363@lst.de> References: <20180224000547.7252-1-keith.busch@intel.com> <20180228163510.GC16002@localhost.localdomain> <20180228163701.GA16363@lst.de> Message-ID: <20180228195411.GJ16002@localhost.localdomain> On Wed, Feb 28, 2018@05:37:01PM +0100, Christoph Hellwig wrote: > On Wed, Feb 28, 2018@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.