Add public function to get cnode's cspace

Needed for CapNet's cn_objref_principal function that is needed for a
correct implementation of rendezvous points.

include/libcap.h

@@ -210,6 +210,11 @@ void* cap_cnode_object(struct cnode *cnode);
  */
 cap_type_t cap_cnode_type(struct cnode *cnode);
 
+/**
+ * Get the cspace this cnode is in.
+ */
+struct cspace * cap_cnode_cspace(struct cnode *cnode);
+
 /**
  * For now, put debug macros in the user-accessible part; convenient.
  */

src/common/cap.c

@@ -451,6 +451,7 @@ void cap_cnode_put(struct cnode *cnode)
 
 void* cap_cnode_object(struct cnode *cnode) { return cnode->object; }
 cap_type_t cap_cnode_type(struct cnode *cnode) { return cnode->type; }
+struct cspace * cap_cnode_cspace(struct cnode *cnode) { return cnode->cspace; }
 
 int cap_cnode_verify(struct cspace *cspace, cptr_t c)
 {