-is standard input (@code{stdin}), fd 1 is standard output
-(@code{stdout}). These special file descriptors are valid as system
-call arguments only as explicitly described below.
-
-Consider implementing this function in terms of @func{filesys_open}.
+(@code{STDIN_FILENO}) is standard input, fd 1 (@code{STDOUT_FILENO}) is
+standard output. The @code{open} system call will never return either
+of these file descriptors, which are valid as system call arguments only
+as explicitly described below.
+
+Each process has an independent set of file descriptors. File
+descriptors are not inherited by child processes.
+
+When a single file is opened more than once, whether by a single
+process or different processes, each @code{open} returns a new file
+descriptor. Different file descriptors for a single file are closed
+independently in separate calls to @code{close} and they do not share
+a file position.