Enabling peer to peer device transactions for PCIe devices

[Jason Gunthorpe]

> > I'm not opposed to mapping /dev/nvmeX.  However, the lookup is trivial
> > to accomplish in sysfs through /sys/dev/char to find the sysfs path of the
> > device-dax instance under the nvme device, or if you already have the nvme
> > sysfs path the dax instance(s) will appear under the "dax" sub-directory.
> 
> Personally I think mapping the dax resource in the sysfs tree is a nice
> way to do this and a bit more intuitive than mapping a /dev/nvmeX.

It is still not at all clear to me what userpsace is supposed to do
with this on nvme.. How is the CMB usable from userspace?

Jason