mm: memory hotplug with an existing resource

Add add_memory_resource() to add memory using an existing "System RAM"
resource.  This is useful if the memory region is being located by
finding a free resource slot with allocate_resource().

Xen guests will make use of this in their balloon driver to hotplug
arbitrary amounts of memory in response to toolstack requests.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Tang Chen <tangchen@cn.fujitsu.com>

include/linux/memory_hotplug.h

@@ -11,6 +11,7 @@ struct zone;
 struct pglist_data;
 struct mem_section;
 struct memory_block;
+struct resource;
 
 #ifdef CONFIG_MEMORY_HOTPLUG
 
@@ -266,6 +267,7 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
 extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
 		void *arg, int (*func)(struct memory_block *, void *));
 extern int add_memory(int nid, u64 start, u64 size);
+extern int add_memory_resource(int nid, struct resource *resource);
 extern int zone_for_memory(int nid, u64 start, u64 size, int zone_default,
 		bool for_device);
 extern int arch_add_memory(int nid, u64 start, u64 size, bool for_device);