A zero special file is a source of zeroed unnamed memory.
Reads from a zero special file always return a buffer full of zeroes. The file is of infinite length.
Writes to a zero special file are always successful, but the data written is ignored.
Mapping a zero special file creates a zero-initialized unnamed memory object of a length equal to the length of the mapping and rounded up to the nearest page size as returned by sysconf. Multiple processes can share such a zero special file object provided a common ancestor mapped the object MAP_SHARED.