Return_Values

   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.