Re: [libvirt-users] How does libvirt interaction with KVM to create a VM?

On 06/28/2012 05:21 PM, Dennis Chen wrote: > All, > > These days I am trying to understand the interaction relationship > between the libvirt and KVM kernel module, eg. kvm_intel.ko. > > We know that KVM kernel module expose an entry in form of device file > "/dev/kvm" which can be accessed by user space application to control, > for example, create a VM using KVM_CREATE_VM with help of ioctl. > > Now let's say the tool virsh based upon libvirt, we can create a guest > domain with the command looks like: > #virsh create guest.xml > Obviously, the above command will create a VM. But when I try to > investigate the libvirt code, I can't find any code play with the > "/dev/kvm" to send KVM_CREATE_VM ioctl code to KVM kernel module. > But I do found that the reference count of the kvm_intel.ko changed > before the virsh create command launched and after. > > So my question is: how does the libvirt interaction with KVM to create > a VM? Anybody can give me some tips about that, eg, the corresponding > codes in libvirt? http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/qemu/qemu_driver.c;h=2... 114 /* device for kvm ioctls */ 115 #define KVM_DEVICE "/dev/kvm" 1022 static int kvmGetMaxVCPUs(void) { 1023 int maxvcpus = 1; 1024 1025 int r, fd; 1026 1027 fd = open(KVM_DEVICE, O_RDONLY); 1028 if (fd< 0) { 1029 virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE); 1030 return -1; 1031 } 1032 1033 r = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); 1034 if (r> 0) 1035 maxvcpus = r; 1036 1037 VIR_FORCE_CLOSE(fd); 1038 return maxvcpus; 1039 }

http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/qemu/qemu_process.c;h=... Please see qemuProcessStart() implemetation: 3288 int qemuProcessStart(virConnectPtr conn, 3289 struct qemud_driver *driver, 3290 virDomainObjPtr vm, 3291 const char *migrateFrom, 3292 int stdin_fd, 3293 const char *stdin_path, 3294 virDomainSnapshotObjPtr snapshot, 3295 enum virNetDevVPortProfileOp vmop, 3296 unsigned int flags) ...... > BRs. > Dennis > > _______________________________________________ > libvirt-users mailing list > libvirt-users(a)redhat.com > https://www.redhat.com/mailman/listinfo/libvirt-users