[PATCH] don't create cpu/online sysfs file

This file provides ability for caller of register_cpu() to either create a
control file, or not.  This can be handy if a particular platform decides
that certain CPU's are not removable.  Hence would like to not create a
control file.
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/sysfs.c

@@ -325,6 +325,16 @@ static int __init topology_init(void)
 #ifdef CONFIG_NUMA
 		parent = &node_devices[cpu_to_node(cpu)];
 #endif
+		/*
+		 * For now, we just see if the system supports making
+		 * the RTAS calls for CPU hotplug.  But, there may be a
+		 * more comprehensive way to do this for an individual
+		 * CPU.  For instance, the boot cpu might never be valid
+		 * for hotplugging.
+		 */
+		if (systemcfg->platform != PLATFORM_PSERIES_LPAR)
+			c->no_control = 1;
+
 		register_cpu(c, cpu, parent);
 
 		register_cpu_pmc(&c->sysdev);

drivers/base/cpu.c

@@ -58,6 +58,8 @@ static inline void register_cpu_control(struct cpu *cpu)
 
 /*
  * register_cpu - Setup a driverfs device for a CPU.
+ * @cpu - Callers can set the cpu->no_control field to 1, to indicate not to
+ *		  generate a control file in sysfs for this CPU.
  * @num - CPU number to use when creating the device.
  *
  * Initialize and register the CPU device.
@@ -75,7 +77,7 @@ 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)
+	if (!error && !cpu->no_control)
 		register_cpu_control(cpu);
 	return error;
 }

include/linux/cpu.h

@@ -27,6 +27,7 @@
 
 struct cpu {
 	int node_id;		/* The node which contains the CPU */
+	int no_control;		/* Should the sysfs control file be created? */
 	struct sys_device sysdev;
 };