unsigned as_find_containing(unsigned off, 
                            paddr_t start, 
                            paddr_t end, 
                            const char *container);

Find an asinfo entry with the name pointed to by container that at least partially covers the range given by start and end. Follows the same rules as as_find() to know where the search starts. Returns the offset of the matching entry or AS_NULL_OFF if none is found. (The as_add_containing() function uses this to find what the owner fields should be for the entries it's adding.)