[fedora-virt] Where do the machine definitions come from?

[Tom Horsley]

I'm upgrading a prehistoric fedora13 machine that hosted
a gazillion virtual machines to centos 7.

I find that the old virtual machine xml files make
the new libvirt barf.

I can get a good idea of how to fix all the old xml
by installing a new file and comparing things, but
I wonder where this magic comes from:

  <os>
    <type arch='x86_64' machine='pc-i440fx-rhel7.0.0'>hvm</type>
    <boot dev='hd'/>
  </os>

Specifically, the "machine" definitions. Should that just
always be the string above since my host is centos 7?