-/* Write COUNT bytes at BUF to descriptor FD, retrying if interrupted
- or if partial writes occur. Return the number of bytes successfully
- written, setting errno if that is less than COUNT. */
+/* Write(read) COUNT bytes at BUF to(from) descriptor FD, retrying if
+ interrupted or if a partial write(read) occurs. Return the number
+ of bytes transferred.
+ When writing, set errno if fewer than COUNT bytes are written.
+ When reading, if fewer than COUNT bytes are read, you must examine
+ errno to distinguish failure from EOF (errno == 0). */