linux pipe

linux pipe 读写分开，读的只能读，写的只能写，写什么，读到的就是什么

    int msgpipe[2];
    if (pipe(msgpipe)) {
        LOG_INFO("could not create pipe: %s", strerror(errno));
        return NULL;
    }

    int8_t cmdr;
    int8_t cmdw = 9;
    write(msgpipe[1], &cmdw, sizeof(cmdw));
    read( msgpipe[0], &cmdr, sizeof(cmdr));