dup \*- duplicate an open file descriptor
(dup = 41.; not in assembler)
a file descriptor returned from
will allocate another file descriptor
The new file descriptor is returned in r0.
is used more to reassign the value
duplicate a file descriptor.
Since the algorithm to allocate
manipulate file descriptors
manipulating standard input and/or
creat (II), open (II), close (II), pipe (II)
the given file descriptor is invalid;
there are already too many open files.
From C, a \*-1 returned value indicates an error.