On Wed, Oct 18, 2017 at 6:03 AM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: > On Tue, Oct 17, 2017 at 04:30:41AM -0400, Pankaj Gupta wrote: >> >> > > Are you saying do it as existing i.e ACPI pmem like interface? >> > > The reason we have created this new driver is exiting pmem driver >> > > does not define proper semantics for guest flushing requests. >> > >> > At this point I'm caring about the Linux-internal interface, and >> > for that it should be integrated into the nvdimm subsystem and not >> > a block driver. How the host <-> guest interface looks is a different >> > idea. >> > >> > > >> > > Regarding block support of driver, we want to achieve DAX support >> > > to bypass guest page cache. Also, we want to utilize existing DAX >> > > capable file-system interfaces(e.g fsync) from userspace file API's >> > > to trigger the host side flush request. >> > >> > Well, if you want to support XFS+DAX better don't make it a block >> > devices, because I'll post patches soon to stop using the block device >> > entirely for the DAX case. >> >> o.k I will look at your patches once they are in mailing list. >> Thanks for the heads up. >> >> If I am guessing it right, we don't need block device additional features >> for pmem? We can bypass block device features like blk device cache flush etc. >> Also, still we would be supporting ext4 & XFS filesystem with pmem? >> >> If there is time to your patches can you please elaborate on this a bit. > > I think the idea is that the nvdimm subsystem already adds block device > semantics on top of the struct nvdimms that it manages. See > drivers/nvdimm/blk.c. > > So it would be cleaner to make virtio-pmem an nvdimm bus. This will > eliminate the duplication between your driver and drivers/nvdimm/ code. > Try "git grep nvdimm_bus_register" to find drivers that use the nvdimm > subsystem. This use case is not "Persistent Memory". Persistent Memory is something you can map and make persistent with CPU instructions. Anything that requires a driver call is device driver managed "Shared Memory".
