On 30/04/2020 11:45, Peter Maydell wrote: > On Thu, 30 Apr 2020 at 11:34, Daniel P. Berrangé <berra...@redhat.com> wrote: >> We "merely" need a new query language targetted to QEMU's qtree >> structure, which we can expose in the CLI that gives unique access >> to every possible property. > > Past resistance to this has been grounded in not wanting to > expose the exact arrangement of the qtree as a user-facing > thing that needs to be maintained for back-compat reasons. > > Eg in your example the i440fx-pcihost sits directly on the > 'system bus', but this is an odd artefact of the old qbus/qdev > system and doesn't really reflect the way the system is built > up in terms of QOM components; we might one day want to > restructure things there, which would AIUI break a > command line like > >> To uniquely identify this we can have a string: >> >> >> /dev[1]/bus[pci/0]/dev[id=balloon0]/bus[virtio-bus]/dev[0]/deflate-on-oom=true
Certainly with the machines that I work on the QOM paths can't be guaranteed to be stable: a good example would be how over time people have fixed up the macio device child devices with refactoring. So if I had a command line that used a QOM path to connect a chardev to the on-board serial port then this change would have caused all of the previously documented examples out on the internet to fail :/ That's why I'm more keen to go with using aliases as per my previous email since then it doesn't matter if the QOM tree structure (accidentally) changes. ATB, Mark.