pg_lo_read( dbh, fd, bufsv, len )
    SV *    dbh
    int     fd
    SV *    bufsv
    size_t  len
CODE:
    int     ret;
    char *  buf;
    if(  SvROK(bufsv)  ) {
        bufsv= SvRV(bufsv);
    }
    sv_setpvn(bufsv,"",0); /* Make sure we can grow it safely */
    buf= SvGROW( bufsv, len + 1 );
    ret= pg_db_lo_read( dbh, fd, buf, len );
    if(  0 < ret  ) {
        SvCUR_set( bufsv, ret );
        *SvEND(bufsv)= '\0';
        SvSETMAGIC( bufsv );
    }
    ST(0)= 0 <= ret
        ? sv_2mortal(newSViv(ret))
        : &PL_sv_undef;