Gerd Hoffmann <kra...@redhat.com> writes: > Hi, > >>> If -hda has the semantics of "create an IDE device", then no, we can't >>> change it. It doesn't however. IIRC on -M pseries -hda creates SCSI >>> devices. On s390 -hda creates virtio devices. So if on -M q35 -hda would >>> create if=ahci, I don't see how that breaks the CLI. >> >> It doesn't per se, that is as long as you need to explicitly specify -M >> q35. But then changing the default machine from the existing pc to q35 >> would break the command line. > > That will happen _anyway_. No doubt there will be configurations which > work with -M pc and break with -M q35.
Yup. Without -M, you get whatever the developer picked for you. If we took backward compatibility dogmatically serious, the default would still be pc-0.10. Fortunately, we don't. We pick something we think makes sense for most users, in particular casual users unaware of -M. Whether and when that will become some q35 machine will be debated when q35 works. If you want the best possible compatibility, use -M FOO, where FOO is whatever machine type you've been using (machine type, not alias, i.e. -M pc-1.2, not -M pc).
