gfs_pio_getline() reads a line from the file gf, and
stores to the buffer starting at s at most size - 1
bytes. It is indistinguishable whether the length of a line is more
than size or equal to size - 1. It sets 1 into the
address pointed by eofp on end of file, otherwise it sets 0.
RETURN VALUES
NULL
The function terminated successfully.
GFARM_ERR_NO_MEMORY
Insufficient memory was available.
Others
An error except the above occurred. The reason is shown by its
pointed strings.