[libvirt] [RFC] New API to retrieve node CPU map

Hi, in order to use the APIs listed below it is necessary for a client to know the maximum number of node CPUs which is passed via the maplen argument. virDomainGetEmulatorPinInfo virDomainGetVcpuPinInfo virDomainGetVcpus virDomainPinEmulator virDomainPinVcpu virDomainPinVcpuFlags The current approach uses virNodeGetInfo to determine the maximum CPU number. This can lead to incorrect results if not all node CPUs are online. The maximum CPU number should always be the number of CPUs present on the host, regardless of their online/offline state. The following example illustrates the issue: Host has 3 logical CPUs, 1 socket, 3 cores, 1 thread. Guest has 1 virtual CPU and is started while all 3 host CPUs are online. $ virsh vcpuinfo guest VCPU: 0 CPU: 0 State: running CPU time: 35.4s CPU Affinity: yyy $ echo 0 > /sys/devices/system/cpu/cpu1/online $ virsh vcpuinfo guest VCPU: 0 CPU: 0 State: running CPU time: 35.5s CPU Affinity: y- The correct display for CPU affinity would have been y-y, as the guest continues to use CPUs 0 and 2. This is not a display problem only, because it is also not possible to explicitly pin the virtual CPU to host CPUs 0 and 2, due to the truncated CPU mask. PROPOSAL: To help solve the issue above I suggest two new public API functions: int virNodeGetCpuNum(virConnectPtr conn); returning the number of present CPUs on the host or -1 upon failure and int virNodeGetCpuMap(virConnectPtr conn, unsigned char * cpumap, int maplen); returning the number of present CPUs or -1 on failure and storing a bit map of real CPUs as described in virDomainPinVcpu in cpumap. The bits in the bit map are set to 1 for online CPUs and set to 0 for offline CPUs. Implementation is facilitated by the function nodeGetCPUmap in nodeinfo.c. Clients can use virNodeGetCpuNum to properly determine the maximum number of node CPUs and the online/offline information. Thanks for your comments. -- Mit freundlichen Grüßen/Kind Regards Viktor Mihajlovski IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Martin Jetter Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen Registergericht: Amtsgericht Stuttgart, HRB 243294