Hello, I'm working on the vpcu patch of Michel Ponceau because he is in vacation for a long time. Michel has proposed to add 3 APIs to libvirt: - virDomainSetVcpus - virDomainPinVcpu - virDomainGetVcpus I've seen in libvirt mail archives that there was a problem with the virDomainGetVcpus API because the virCpuInfo structure contains a CPU map for only 256 physical CPUs. Your proposition to remove cpumap field from virCpuInfo structure and add it as parameter to the virDomainGetVcpus API isn't valid for the following reason: The virDomainGetVcpus API fills an array of virCpuInfo structures (one virCpuInfo for one VCPU) but cpumap is for one VCPU, not for all VCPUs at whole. Your proposition can work only if cpumap is a array of array of characters and if maplen is also an array of integers. This is very complicated solution and not elegant. I've also seen that you make a mistake in your proposition because you compute the cpuMapLen from the number of virtual CPUs but the cpumap is related to physical CPUs, not virtual CPUs. So, in conclusion, I propose, as you, to remove cpumap field of the virCpuInfo structure but to add an API to retrieve the CPU map of one VCPU. Such API would be: int virDomainGetCpus(virDomainPtr domain, unsigned int vcpu, unsigned char *cpumap, int maplen); The name is ...GetCpus (not 'Vcpus') because this API get the physical CPU map, not the virtual CPU map. Regards, Philippe Berthault.