[libvirt] [RFC] Per machine type qemu capability detection

[Peter Krempa]

Hi,

qemu recently added a qmp/hmp command ("get-cpu-max") to determine 
maximum number of supported CPUs for a VM. The output of this command 
depends on the machine type that is used when it is called. The problem 
here is that libvirt uses "-M none" while detecting capabilities and 
with that machine type the get-cpu-max command returns always 1.

My question is: Is it worthwhile to do per machine type capability 
detection? It definitely isn't worth doing just for the get-cpu-max 
support, but it might be needed for Q35 or other stuff that may depend 
on the actual machine type used.

Pros of this approach:
----------------------
- (possibly) more accurate capabilities


Cons:
-----
- ~10x more qemus started on libvirtd startup (one per machine type)


Thanks for your opinions.


Peter