resources: Add resource_shrink_parents_top()

We use it to shrink the resource top of parents that could be expanded
before.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 43 insertions, 0 deletions

diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index 589e0e75efae2d..43d5e451cf9e28 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -156,6 +156,8 @@ extern int allocate_resource(struct resource *root, struct resource *new,
 						       resource_size_t,
 						       resource_size_t),
 			     void *alignf_data);
+int resource_shrink_parents_top(struct resource *b_res,
+				 long size, struct resource *parent_res);
 struct resource *lookup_resource(struct resource *root, resource_size_t start);
 int adjust_resource(struct resource *res, resource_size_t start,
 		    resource_size_t size);
diff --git a/kernel/resource.c b/kernel/resource.c
index efbbe9f5d2bbd9..50c36fb4dbcd35 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1020,6 +1020,47 @@ void __release_region(struct resource *parent, resource_size_t start,
 }
 EXPORT_SYMBOL(__release_region);
 
+static int __resource_shrink_parents_top(struct resource *b_res,
+		 long size, struct resource *parent_res)
+{
+	struct resource *res = b_res;
+
+	if (size <= 0)
+		return 0;
+
+	while (res && res != parent_res) {
+		if (__adjust_resource(res, res->start,
+			 resource_size(res) - size)) {
+			struct resource *tmp = b_res;
+
+			/* roll back */
+			while (tmp != res) {
+				__adjust_resource(tmp, tmp->start,
+					resource_size(tmp) + size);
+				tmp = tmp->parent;
+			}
+
+			return -EBUSY;
+
+		}
+		res = res->parent;
+	}
+
+	return 0;
+}
+
+int resource_shrink_parents_top(struct resource *b_res,
+		 long size, struct resource *parent_res)
+{
+	int ret;
+
+	write_lock(&resource_lock);
+	ret = __resource_shrink_parents_top(b_res, size, parent_res);
+	write_unlock(&resource_lock);
+
+	return ret;
+}
+
 /*
  * Managed region resource
  */