Added some more signatures

src/backing.h

@@ -26,6 +26,10 @@ bool backing_exists(const char* backing);
 /// @return The list of backing disks. The caller is responsible for freeing the returned array and strings. This function can return NULL.
 char** list_backings(void);
 
+/// @brief Finds the latest backing disk.
+/// @return The latest backing disk. The caller is responsible for freeing the returned string. This function can return NULL.
+char* find_latest_backing(void);
+
 /// @brief Creates a new backing disk.
 /// @param backing_disk The disk to use as the backing disk. Warning: the disk must be part of the backing disks.
 /// @return true if the backing disk was created, otherwise false.