if (maskset) {
                rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
                              TASKSTATS_CMD_ATTR_REGISTER_CPUMASK,
-                             &cpumask, sizeof(cpumask));
+                             &cpumask, strlen(cpumask) + 1);
                PRINTF("Sent register cpumask, retval %d\n", rc);
                if (rc < 0) {
                        printf("error sending register cpumask\n");
                }
                if (msg.n.nlmsg_type == NLMSG_ERROR ||
                    !NLMSG_OK((&msg.n), rep_len)) {
-                       printf("fatal reply error,  errno %d\n", errno);
+                       struct nlmsgerr *err = NLMSG_DATA(&msg);
+                       printf("fatal reply error,  errno %d\n", err->error);
                        goto done;
                }
 
        if (maskset) {
                rc = send_cmd(nl_sd, id, mypid, TASKSTATS_CMD_GET,
                              TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK,
-                             &cpumask, sizeof(cpumask));
+                             &cpumask, strlen(cpumask) + 1);
                printf("Sent deregister mask, retval %d\n", rc);
                if (rc < 0)
                        err(rc, "error sending deregister cpumask\n");