Re: [libvirt] [Qemu-devel] libvirt<->QEMU interfaces for CPU models
Am 01.03.2013 14:12, schrieb Jiri Denemark:
On Thu, Feb 21, 2013 at 11:58:18 -0300, Eduardo Habkost wrote:
> = Listing CPU models =
>
> Requirement: libvirt needs to know which CPU models are available to be used
> with the "-cpu" option.
>
> Current problem: libvirt relies on help output parsing for that.
query-cpu-definitions is the QMP command to retrieve values compatible
with -cpu.
And if libvirt is not using it, I really don't understand why the work
of maintaining this crappy interface has been pushed onto us in the
first place? There is no reuse between -cpu ? and QMP implementations so
it's just extra work, there is no communicated or implemented way to
extend the arch_query_cpu_definitions() implementation to become more
usable for command line output implementation (e.g., associating a PVR
value with the model name for ppc) and, while we're at it, it uses
global functions plus a stub rather than a CPUState hook with a no-op
default implementation in qom/cpu.c...
> Solution: use QMP qom-list-types command.
>
> Dependency: X86CPU subclasses.
> Limitation: needs a live QEMU process for the query.
No problem, we already run QEMU and use several QMP commands to probe
its capabilities. And "qom-list-types" is actually one of them. To get
the list of CPU models, we would just call
{
"execute": "qom-list-types",
"arguments": {
"implements": "X86CPU"
}
}
right?
Not quite, this would return abstract types as well, so you'd need to
add "abstract": "false" or so.
And you need to use the type name, not the struct name as argument, i.e.
"i386-cpu" or "x86_64-cpu". Note: This does not always match the
executable name since QOM names are supposed to be verbose (e.g., ppc64
vs. powerpc64-cpu) and some executables are misnamed (sh4 vs. superh-cpu).
For x86 today this will return one type, either "i386-cpu" or
"x86_64-cpu", that's why I have been pushing to implement model
subclasses. There's still some controversial discussions about how this
relates to KVM and TCG changing values of classes.
What about other non-x86 architectures?
For some other architectures like arm this will return the full list of
available classes, but in "cortex-a9-arm-cpu" format, which is not
guaranteed to be compatible with -cpu but rather with -device where
already applicable.
Will we need to use
different class name or is there a generic CPU class that could be used
universally?
"cpu" would currently work as well, but the CPU refactorings are
targetting to compile, e.g., arm-cpu and microblaze-cpu types into the
same executable, so "cpu" may lead to undesired results in the future
depending on what assumptions your code makes.
Regards,
Andreas
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