cpu_hotplug.c
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#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
#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[16], state[16];
sprintf(dir, "cpu/%u", cpu);
err = xenbus_scanf(XBT_NIL, dir, "availability", "%15s", state);
if (err != 1) {
if (!xen_initial_domain())
pr_err("Unable to read cpu state\n");
return err;
}
if (strcmp(state, "online") == 0)
return 1;
else if (strcmp(state, "offline") == 0)
return 0;
pr_err("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);