[PATCH] Hotplug CPUs: Sysfs Online Attribute

Add "online" sysfs attribute to cpus to bring them up and down.

Again, only under CONFIG_HOTPLUG_CPU.

drivers/base/cpu.c

@@ -7,6 +7,7 @@
 #include <linux/init.h>
 #include <linux/cpu.h>
 #include <linux/topology.h>
+#include <linux/device.h>
 
 
 struct sysdev_class cpu_sysdev_class = {
@@ -14,6 +15,46 @@ struct sysdev_class cpu_sysdev_class = {
 };
 EXPORT_SYMBOL(cpu_sysdev_class);
 
+#ifdef CONFIG_HOTPLUG_CPU
+static ssize_t show_online(struct sys_device *dev, char *buf)
+{
+	struct cpu *cpu = container_of(dev, struct cpu, sysdev);
+
+	return sprintf(buf, "%u\n", !!cpu_online(cpu->sysdev.id));
+}
+
+static ssize_t store_online(struct sys_device *dev, const char *buf,
+			    size_t count)
+{
+	struct cpu *cpu = container_of(dev, struct cpu, sysdev);
+	ssize_t ret;
+
+	switch (buf[0]) {
+	case '0':
+		ret = cpu_down(cpu->sysdev.id);
+		break;
+	case '1':
+		ret = cpu_up(cpu->sysdev.id);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret >= 0)
+		ret = count;
+	return ret;
+}
+static SYSDEV_ATTR(online, 0600, show_online, store_online);
+
+static void __init register_cpu_control(struct cpu *cpu)
+{
+	sysdev_create_file(&cpu->sysdev, &attr_online);
+}
+#else /* ... !CONFIG_HOTPLUG_CPU */
+static inline void register_cpu_control(struct cpu *cpu)
+{
+}
+#endif /* CONFIG_HOTPLUG_CPU */
 
 /*
  * register_cpu - Setup a driverfs device for a CPU.
@@ -34,6 +75,8 @@ int __init register_cpu(struct cpu *cpu, int num, struct node *root)
 		error = sysfs_create_link(&root->sysdev.kobj,
 					  &cpu->sysdev.kobj,
 					  kobject_name(&cpu->sysdev.kobj));
+	if (!error)
+		register_cpu_control(cpu);
 	return error;
 }