resource: add release_child_resources

Useful for freeing a portion of the resource tree, e.g. when trying to
reallocate resources more efficiently.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

include/linux/ioport.h

@@ -112,6 +112,7 @@ extern struct resource iomem_resource;
 
 extern int request_resource(struct resource *root, struct resource *new);
 extern int release_resource(struct resource *new);
+void release_child_resources(struct resource *new);
 extern void reserve_region_with_split(struct resource *root,
 			     resource_size_t start, resource_size_t end,
 			     const char *name);

kernel/resource.c

@@ -188,6 +188,36 @@ static int __release_resource(struct resource *old)
 	return -EINVAL;
 }
 
+static void __release_child_resources(struct resource *r)
+{
+	struct resource *tmp, *p;
+	resource_size_t size;
+
+	p = r->child;
+	r->child = NULL;
+	while (p) {
+		tmp = p;
+		p = p->sibling;
+
+		tmp->parent = NULL;
+		tmp->sibling = NULL;
+		__release_child_resources(tmp);
+
+		printk(KERN_DEBUG "release child resource %pR\n", tmp);
+		/* need to restore size, and keep flags */
+		size = resource_size(tmp);
+		tmp->start = 0;
+		tmp->end = size - 1;
+	}
+}
+
+void release_child_resources(struct resource *r)
+{
+	write_lock(&resource_lock);
+	__release_child_resources(r);
+	write_unlock(&resource_lock);
+}
+
 /**
  * request_resource - request and reserve an I/O or memory resource
  * @root: root resource descriptor