[libvirt] [RFC] Support cpu hotplug in libvirt.

Hi~ It seems that libvirt is not cpu hotplug aware. Please refer to the following problem. 1. At first, we have 2 cpus. # cat /cgroup/cpuset/cpuset.cpus 0-1 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0-1 2. And we have a vm1 with following configuration. <cputune> <vcpupin vcpu='0' cpuset='1'/> <hypervisorpin cpuset='1'/> </cputune> 3. Offline cpu1. # echo 0 > /sys/devices/system/cpu/cpu1/online # cat /sys/devices/system/cpu/cpu1/online 0 # cat /cgroup/cpuset/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0 4. Online cpu1. # echo 1 > /sys/devices/system/cpu/cpu1/online # cat /sys/devices/system/cpu/cpu1/online 1 # cat /cgroup/cpuset/cpuset.cpus 0-1 # cat /cgroup/cpuset/libvirt/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/lxc/cpuset.cpus 0 Here，cgroup updated cpuset.cpus，but not for libvirt directory，and also qemu and lxc directory. vm1 cannot be started again. # virsh start vm1 error: Failed to start domain vm1 error: Unable to set cpuset.cpus: Permission denied And libvird gave the following errors. 2012-07-17 07:30:22.478+0000: 3118: error : qemuSetupCgroupVcpuPin:498 : Unable to set cpuset.cpus: Permission denied I am trying to use netlink socket with NETLINK_KOBJECT_UEVENT protocol to listen to cpu hotplug events. But I met a little problem here. virNetlinkEventServiceStart() only create a global variable server, and create a NETLINK_ROUTE netlink socket for it. So if I want to create another different netlink socket, such as NETLINK_KOBJECT_UEVENT, what should I do ? Shall we make the server global variable a global array ? (It seems there are a lot of work to do.) Thanks. :) -- Best Regards, Tang chen