cpu_hotplug.c

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#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) {
        if (!xen_initial_domain())
            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);