TCP套接字的Linux时间戳

Question

我正在一个项目中工作，以从Linux timestamping获得接收和传输时间戳，如文档Linux timestamping中提到的那样。但是所有的文档和测试编码都是针对UDP套接字完成的。但是我得到的是NIC的传输时间戳，而不是接收TCP数据包的时间戳。

我的接口支持以下时间戳

    Time stamping parameters for enp4s0:
Capabilities:
    hardware-transmit     (SOF_TIMESTAMPING_TX_HARDWARE)
    software-transmit     (SOF_TIMESTAMPING_TX_SOFTWARE)
    hardware-receive      (SOF_TIMESTAMPING_RX_HARDWARE)
    software-receive      (SOF_TIMESTAMPING_RX_SOFTWARE)
    software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
    hardware-raw-clock    (SOF_TIMESTAMPING_RAW_HARDWARE)
PTP Hardware Clock: 3
Hardware Transmit Timestamp Modes:
    off                   (HWTSTAMP_TX_OFF)
    on                    (HWTSTAMP_TX_ON)
Hardware Receive Filter Modes:
    none                  (HWTSTAMP_FILTER_NONE)
    all                   (HWTSTAMP_FILTER_ALL)

我在bind()之后启用NIC的时间戳，使用ioctl(sockfd, SIOCSHWTSTAMP, &net_device);

memset(&net_device, 0, sizeof(net_device));
strncpy(net_device.ifr_name, interface_name, sizeof(net_device.ifr_name));
net_device.ifr_data = (void *)&tstconfig;
memset(&tstconfig, 0, sizeof(tstconfig));

tstconfig.tx_type = HWTSTAMP_TX_OFF;
tstconfig.rx_filter = HWTSTAMP_FILTER_ALL;

然后通过setsockopt()在网卡中启用时间戳。

int opt= 0;
opt |= SOF_TIMESTAMPING_RX_HARDWARE;
opt |= SOF_TIMESTAMPING_RAW_HARDWARE;
if (setsockopt(sockfd, SOL_SOCKET, SO_TIMESTAMPING,
           (char *)&opt, sizeof(opt))) {
    error(1, 0, "setsockopt timestamping");
    bail("setsockopt SO_TIMESTAMPING");
}

在listen()和accept()之后，我执行select()，并检查fd是否是rfds，然后使用以下选项调用recvmsg()

int rc;
struct iovec vec[1];
struct msghdr msg;
char data[8192];
struct cmsghdr *cmsg;

union {
    struct cmsghdr cm;
    char control[256];
} cmsg_un;

vec[0].iov_base = data;
vec[0].iov_len = sizeof(data);

memset(&msg, 0, sizeof(msg));
memset(&from_addr, 0, sizeof(from_addr));
memset(&cmsg_un, 0, sizeof(cmsg_un));

msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = vec;
msg.msg_iovlen = 1;
msg.msg_control = cmsg_un.control;
msg.msg_controllen = sizeof(cmsg_un.control);   
rc = recvmsg(flow->fd, &msg, 0);

printf("tried reading %d bytes, got %d", bytes, rc);
if (msg.msg_flags & MSG_TRUNC) {
    printf("received truncated message\n");
    return 0;
}

if (msg.msg_flags & MSG_CTRUNC) {
    printf("received truncated ancillary data\n");
    return 0;
}

if (msg.msg_controllen <= 0) {
    printf("`received short ancillary data (%ld/%ld)`\n",
            (long)msg.msg_controllen, (long)sizeof(cmsg_un.control));
    return 0;
}

但我总是收到以下信息，

received short ancillary data (0/256)

我没有从recvmsg()获得辅助数据，我想知道linux是否收到NIC的硬件时间戳。

Answer 1

Linux时间戳不支持TCP的接收硬件或软件时间戳。linux时间戳的文档只在“数据包”方面提到。这是指UDP，它用于实现NIC中PTP硬件时钟的同步，请参阅PTP守护进程和linux的代码，以获得更多的了解。Linux 3.18只支持传输中的时间戳。因此，基本上您不能在接收端实现TCP的linux时间戳。

Answer 2

我能够使用最近的内核版本(4.18)使用带有TCP套接字的SO_TIMESTAMPING。这适用于TX和RX时间戳。我仍在研究这个问题，但如果你愿意的话，我可以尝试写一个概念的最小证明。