n                  The number of bytes read.
    -1                 Indicates a read error. The function sets
                       errno to one of the following values:

                       o  EAGAIN - The O_NONBLOCK flag is set for the
                          file descriptor, and the process would be
                          delayed.

                       o  EBADF - The file_desc argument is not a
                          valid file descriptor open for reading.

                       o  EBADMSG - The file is a STREAM file that is
                          set to control-normal mode, and the message
                          waiting to be read includes a control part.

                       o  EINTER - The read operation was terminated
                          because of the receipt of a signal, and no
                          data was transferred.

                       o  EINVAL - The STREAM or multiplexer
                          referenced by file_desc is linked
                          (directly or indirectly) downstream from
                          a multiplexer.

                          OR

                          The sum of the iov_len values in the iov
                          array overflowed an ssize_t.

                       o  EIO - A physical I/O error has occurred.

                          OR

                          The process is a member of a background
                          process attempting to read from its
                          controlling terminal, the process is
                          ignoring or blocking the SIGTTIN signal,
                          or the process group is orphaned.

                       o  EISDIR - The file_desc argument refers to a
                          directory, and the implementation does not
                          allow the directory to be read using read,
                          pread or readv. Use the readdir function
                          instead.

                       o  EOVERFLOW - The file is a regular file,
                          nbyte is greater than 0, and the starting
                          position is before the end-of-file and is
                          greater than or equal to the offset maximum
                          established in the open file description
                          associated with file_desc.

                       The readv function may fail if:

                       o  EINVAL - The iovcnt argument was less than
                          or equal to 0, or greater than IOV_MAX.