I did some research on that stuff now. dax hasn’t been merged into QEMU, so it’s not something that can be used. There’s similarly no versiontable mention within the current QEMU codebase which makes me think that ireg has similarly not made it upstream yet.
On the cache front, we’re actually going to be switching to cache=never as the default of cache=auto actually causes issues with systems accessing a very large number of files.
cache=always has some reports of potential data loss/corruption happening, so I don’t think it’s something we’d feel very confident in offering at this point.