Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver

[Christoph Hellwig]

On Tue, Oct 17, 2017 at 03:40:56AM -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.