Re: [RFC v2 1/2] virtio: add pmem driver

[Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Wed, Apr 25, 2018 at 4:24 AM, Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> This patch adds virtio-pmem driver for KVM
> guest.

Minor nit, please expand your changelog line wrapping to 72 columns.

>
> Guest reads the persistent memory range
> information from Qemu over VIRTIO and registers
> it on nvdimm_bus. It also creates a nd_region
> object with the persistent memory range
> information so that existing 'nvdimm/pmem'
> driver can reserve this into system memory map.
> This way 'virtio-pmem' driver uses existing
> functionality of pmem driver to register persistent
> memory compatible for DAX capable filesystems.

We need some additional enabling to disable MAP_SYNC for this
configuration. In other words, if fsync() is required then we must
disable the MAP_SYNC optimization. I think this should be a struct
dax_device property looked up at mmap time in each MAP_SYNC capable
->mmap() file operation implementation.