Added some more unimplemented functions

src/backing.h

@@ -26,6 +26,11 @@ 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 Get the creation time of the specified backing disk.
+/// @param backing The valid backing disk name.
+/// @return The creation time of the specified backing disk. If the backing disk does not exist, this function returns 0.
+uint64_t get_backing_creation_time(const char* backing);
+
 /// @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);