cma: Introduce cma_for_each_area

Frameworks (e.g. Ion) may want to iterate over each possible CMA area to
allow for enumeration. Introduce a function to allow a callback.

Signed-off-by: Laura Abbott <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/cma.h

···
 extern struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 			      gfp_t gfp_mask);
 extern bool cma_release(struct cma *cma, const struct page *pages, unsigned int count);
+
+extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data);
 #endif

mm/cma.c

···
 
 	return true;
 }
+
+int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data)
+{
+	int i;
+
+	for (i = 0; i < cma_area_count; i++) {
+		int ret = it(&cma_areas[i], data);
+
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}