TCP 套接字的 Linux 时间戳

Question

我正在一个项目中工作，以获取来自 NIC 的 TCP 套接字的接收和传输时间戳，如文档 Linux timestamping 中所述.但是所有文档和测试编码都是针对 UDP 套接字完成的。但是我得到了 NIC 的传输时间戳，但没有得到接收 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)

我在 bind() 之后使用 ioctl(sockfd, SIOCSHWTSTAMP, &net_device); 和

为 NIC 启用时间戳

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 是否为 rfds 然后调用 recvmsg() 具有以下选项

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;
}

但我总是收到以下消息，

received short ancillary data (0/256)

我没有从 recvmsg() 获取辅助数据，我想知道 linux 是否支持 NIC 的 TCP 接收硬件时间戳。

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。我仍在努力解决这个问题，但如果您愿意，我可以尝试编写一个最小的概念证明。