PACKET_MMAP的一些问题

本文介绍了PACKET_MMAP的一些问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正在使用packet_mmap读取UDP数据包的快速流.使用以下任一代码段等待传入的帧时，效果很好:

I'm using packet_mmap to read a fast stream of UDP packets. When using either of the following code segments to wait for incoming frames it works fine:

// ring[i].iov_base points to the start address of the ith frame
struct tpacket_hdr *header = (struct tpacket_hdr *) ring[i].iov_base;

// Using poll on socket to wait for data
while(!(header -> tp_status & TP_STATUS_USER))
    {
        struct pollfd pfd;
        pfd.fd      = _socket;
        pfd.events  = POLLIN | POLLERR;
        pfd.revents = 0;
        poll(&pfd, 1, -1);
    }

// Using nanosleep to wait for incoming data
while(!(header -> tp_status & TP_STATUS_USER))
    {
        struct timespec t, r;
        t.tv_nsec = 1;
        t.tv_sec = 0; 
        nanosleep(&t, &r)
    }

但是，当我尝试忙于等待时(while(!(header -> tp_status & TP_STATUS_USER)) ;，在读取了几个数据包后，该语句将无限期保持为True.这是为什么呢?内核仅在发出系统调用时才将帧传输到环形缓冲区吗?输入套接字初始化为:socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP)).

However when I try to busy wait (while(!(header -> tp_status & TP_STATUS_USER)) ; the statement remains True indefinitely after a few packets are read. Why is this so? Does the kernel only transfer frames to the ring buffer when a system call is issued? The input socket is initialised as so: socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP)).

此外，在使用此代码(使用poll或nanosleep)时，它似乎正在丢弃数据包，而使用UDP套接字的简单接收代码却没有，这使得packet_mmap的实现速度变慢.有时套接字会检测到丢弃的数据包，但是当对getsockopt使用PACKET_STATISTICS选项时:

Also, when using this code (using poll or nanosleep) it seems to be dropping packets, whilst a simple receive code using a UDP socket doesn't, making the packet_mmap implementation slower. Sometimes the dropped packets are detected by the sockets, however when using the PACKET_STATISTICS option to getsockopt:

    if (header -> tp_status & TP_STATUS_LOSING)
    {
        struct tpacket_stats stats;
        socklen_t size_sock = sizeof(tpacket_stats);
        if (getsockopt(_socket, SOL_PACKET, PACKET_STATISTICS, &stats, &size_sock) > -1)
            printf("Dropped packets: [%d, %d]\n", stats.tp_drops, stats.tp_packets);
    }

它声明没有数据包被丢弃(输出示例:已丢弃的数据包:[0，5]"). PACKET_STATISTICS在PACKET_RX_RING套接字上的行为是否有所不同?

it states that no packets were dropped (output example: "Dropped packets: [0, 5]"). Does PACKET_STATISTICS behave differently on PACKET_RX_RING sockets?

此代码的完整代码列表可用这里

The full code listing for this code is available here

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PACKET_MMAP的一些问题

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