#include <linux/notifier.h> #include <xen/xen.h>#include <xen/xenbus.h> #include <asm/xen/hypervisor.h>#include <asm/cpu.h> static void enable_hotplug_cpu(int cpu){	if (!cpu_present(cpu))		arch_register_cpu(cpu); 	set_cpu_present(cpu, true);} static void disable_hotplug_cpu(int cpu){	if (cpu_present(cpu))		arch_unregister_cpu(cpu); 	set_cpu_present(cpu, false);} static int vcpu_online(unsigned int cpu){	int err;	char dir[32], state[32]; 	sprintf(dir, "cpu/%u", cpu);	err = xenbus_scanf(XBT_NIL, dir, "availability", "%s", state);	if (err != 1) {		printk(KERN_ERR "XENBUS: Unable to read cpu state\n");		return err;	} 	if (strcmp(state, "online") == 0)		return 1;	else if (strcmp(state, "offline") == 0)		return 0; 	printk(KERN_ERR "XENBUS: unknown state(%s) on CPU%d\n", state, cpu);	return -EINVAL;}static void vcpu_hotplug(unsigned int cpu){	if (!cpu_possible(cpu))		return; 	switch (vcpu_online(cpu)) {	case 1:		enable_hotplug_cpu(cpu);		break;	case 0:		(void)cpu_down(cpu);		disable_hotplug_cpu(cpu);		break;	default:		break;	}} static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,					const char **vec, unsigned int len){	unsigned int cpu;	char *cpustr;	const char *node = vec[XS_WATCH_PATH]; 	cpustr = strstr(node, "cpu/");	if (cpustr != NULL) {		sscanf(cpustr, "cpu/%u", &cpu);		vcpu_hotplug(cpu);	}} static int setup_cpu_watcher(struct notifier_block *notifier,			      unsigned long event, void *data){	int cpu;	static struct xenbus_watch cpu_watch = {		.node = "cpu",		.callback = handle_vcpu_hotplug_event}; 	(void)register_xenbus_watch(&cpu_watch); 	for_each_possible_cpu(cpu) {		if (vcpu_online(cpu) == 0) {			(void)cpu_down(cpu);			set_cpu_present(cpu, false);		}	} 	return NOTIFY_DONE;} static int __init setup_vcpu_hotplug_event(void){	static struct notifier_block xsn_cpu = {		.notifier_call = setup_cpu_watcher }; 	if (!xen_pv_domain())		return -ENODEV; 	register_xenstore_notifier(&xsn_cpu); 	return 0;} arch_initcall(setup_vcpu_hotplug_event);