Linux套接字的Linux时间戳

Question

我正在一个项目中工作,以便从文件Linux时间戳记中提到的用于TCP套接字的NIC获取接收和传输 时间戳.但所有文档和测试编码都是针对UDP套接字完成的.但我正在获取NIC的传输时间戳,而不是获取接收TCP数据包的时间戳.

我的界面支持以下时间戳

    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)

我启用网卡时间戳后bind()用ioctl(sockfd, SIOCSHWTSTAMP, &net_device);用

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;

然后启用NIC中的时间戳 setsockopt()

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");
}

后听()和accept(),我做的select(),并检查是否fd被rfds随后致电recvmsg()与下列选项

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;
}

但我总是得到以下消息,

received short ancillary data (0/256)

我没有从中获取辅助数据recvmsg(),我想知道linux是否支持TCP接收NIC的硬件时间戳.

Answer 1

我能够使用最新内核版本（4.18）将 SO_TIMESTAMPING 与 TCP 套接字一起使用。这适用于 TX 和 RX 时间戳。我仍在研究这个问题，但如果您愿意，我可以尝试编写一个最小的概念证明。

Answer 2

Linux 时间戳不支持 TCP 的接收硬件或软件时间戳。Linux 时间戳的文档仅在“数据包”方面提到。这里指的是UDP，用于实现网卡中PTP硬件时钟的同步，具体可以看PTP daemon和linux ptp的代码。Linux 3.18 仅支持传输时间戳。所以基本上你无法在接收器中实现 TCP 的 Linux 时间戳。