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

[Daniel P. Berrange]

On Thu, Apr 04, 2013 at 06:20:05PM +0200, Peter Krempa wrote:
> 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)

That "con" simply rules it out entirely, not matter what "pro"
points there may be I'm afraid.

For your example here though, why do we need a capabiltiy for that?
Can't we just call get-cpu-max from the specific libvirt API calls
that actually want that info.

Daniel
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