[Libguestfs] [PATCH supermin] Add support for a DAX root filesystem.

[Richard W.M. Jones]

DAX is explained in detail here:
https://lwn.net/Articles/610174/

This patch adds support to supermin for using a DAX root filesystem.
The corresponding libguestfs patches will be posted shortly once I've
tested them a bit more.

This requires qemu >= 2.6.

Unfortunately it's not really a win for a few reasons:

 - Requires enabling ACPI, which slows everything down by hundreds of
   milliseconds.  I need to work out exactly what's going on here.
   Since we never required ACPI before now, I never had the impetus to
   find out if this is easy to fix.

 - The extra modules in the supermin mini-initrd greatly increase its
   size, which also slows things down.  qemu fw_cfg DMA should help
   here, if we ever manage to get it upstream.

 - vNVDIMM and DAX are not very widely tested or used yet.

 - Not supported at all by libvirt.

Rich.