cpumask: mm_cpumask for accessing the struct mm_struct's cpu_vm_mask.

This allows us to change the representation (to a dangling bitmap)
without breaking all the callers: they can use mm_cpumask() now and
won't see a difference as the changes roll into linux-next.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 include/linux/mm_types.h |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -276,4 +276,7 @@ struct mm_struct {
 #endif
 };
 
+/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
+#define mm_cpumask(mm) (&(mm)->cpu_vm_mask)
+
 #endif /* _LINUX_MM_TYPES_H */