s = strftime (buf, bufsize, "%H:%M:%S", &now);
bufsize -= s;
s += snprintf (&buf[s], bufsize, ".%06" PRId64, (int64_t) tv.tv_usec);
s = strftime (buf, bufsize, "%H:%M:%S", &now);
bufsize -= s;
s += snprintf (&buf[s], bufsize, ".%06" PRId64, (int64_t) tv.tv_usec);