pg_lo_read(dbh, fd, buf, len)
        SV * dbh
        int fd
        char * buf
        size_t len
        PREINIT:
                SV * const bufsv = SvROK(ST(2)) ? SvRV(ST(2)) : ST(2);
                int ret;
        CODE:
                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 (ret > 0) {
                        SvCUR_set(bufsv, ret);
                        *SvEND(bufsv) = '\0';
                        sv_setpvn(ST(2), buf, (unsigned)ret);
                        SvSETMAGIC(ST(2));
                }
                ST(0) = (ret >= 0) ? sv_2mortal(newSViv(ret)) : &PL_sv_undef;