CORE_BUF_SIZE
compm, CORE_BUF_SIZE,
tmpbuf = malloc(CORE_BUF_SIZE, M_TEMP, M_WAITOK | M_ZERO);
sb = sbuf_new(NULL, NULL, CORE_BUF_SIZE, SBUF_FIXEDLEN);
chunk_len = MIN(len, CORE_BUF_SIZE);