Paul Brook <paul(a)codesourcery.com&gt; writes: Can also be an indication that the device can't support multiple instances. For instance: commit 39a51dfda835a75c0ebbfd92705b96e4de77f795 Author: Markus Armbruster <armbru(a)redhat.com&gt; Date: Tue Oct 27 13:52:13 2009 +0100 qdev: Tag isa-fdc, PIIX3 IDE and PIIX4 IDE as no-user These devices are created automatically, and attempting to create another one with -device fails with "qemu: hardware error: register_ioport_write: invalid opaque". Signed-off-by: Markus Armbruster <armbru(a)redhat.com&gt; Signed-off-by: Anthony Liguori <aliguori(a)us.ibm.com&gt; With no-user, we at least fail with a decent error message. I don't think it's fair to demand that a qdev conversion must relax restrictions that haven't otherwise bothered us to be correct and proper. We'll relax them if and when they bother us enough to make somebody send a decent patch. And yes, there are better ways to disallow multiple instances of a device than declaring it no-user. Patches welcome.