int level = BT_SECURITY_HIGH;
int err = setsockopt(l2cap_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
                     sizeof(level));
if (err == -1) {
    perror("setsockopt");
    return 1;
}

int defer_setup = 1;
int err = setsockopt(l2cap_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
                     &defer_setup, sizeof(defer_setup));
if (err == -1) {
    perror("setsockopt");
    return err;
}
err = listen(l2cap_socket, 5);
if (err) {
    perror("listen");
    return err;
}
struct sockaddr_l2 remote_addr = {0};
socklen_t addr_len = sizeof(remote_addr);
int new_socket = accept(l2cap_socket, (struct sockaddr*)&remote_addr,
                        &addr_len);
if (new_socket < 0) {
    perror("accept");
    return new_socket;
}
/* To complete the connection setup of new_socket read 1 byte */
char c;
struct pollfd pfd;
memset(&pfd, 0, sizeof(pfd));
pfd.fd = new_socket;
pfd.events = POLLOUT;
err = poll(&pfd, 1, 0);
if (err) {
    perror("poll");
    return err;
}
if (!(pfd.revents & POLLOUT)) {
    err = read(sk, &c, 1);
    if (err < 0) {
        perror("read");
        return err;
    }
}

int flags = SOF_TIMESTAMPING_SOFTWARE |
    SOF_TIMESTAMPING_RX_SOFTWARE;
setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &flags, sizeof(flags));

char data_buf[256];
union {
    char buf[CMSG_SPACE(sizeof(struct scm_timestamping))];
    struct cmsghdr align;
} control;
struct iovec data = {
    .iov_base = data_buf,
    .iov_len = sizeof(data_buf),
};
struct msghdr msg = {
    .msg_iov = &data,
    .msg_iovlen = 1,
    .msg_control = control.buf,
    .msg_controllen = sizeof(control.buf),
};
struct scm_timestamping tss;
res = recvmsg(fd, &msg, MSG_ERRQUEUE | MSG_DONTWAIT);
if (res < 0)
    goto error;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING)
        memcpy(&tss, CMSG_DATA(cmsg), sizeof(tss));
}
tstamp_clock_realtime = tss.ts[0];

int flags = SOF_TIMESTAMPING_SOFTWARE |
    SOF_TIMESTAMPING_TX_SOFTWARE |
    SOF_TIMESTAMPING_TX_COMPLETION |
    SOF_TIMESTAMPING_OPT_ID;
setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &flags, sizeof(flags));

union {
    char buf[2 * CMSG_SPACE(sizeof(struct scm_timestamping))];
    struct cmsghdr align;
} control;
struct iovec data = {
    .iov_base = NULL,
    .iov_len = 0
};
struct msghdr msg = {
    .msg_iov = &data,
    .msg_iovlen = 1,
    .msg_control = control.buf,
    .msg_controllen = sizeof(control.buf),
};
struct cmsghdr *cmsg;
struct scm_timestamping tss;
struct sock_extended_err serr;
int res;
res = recvmsg(fd, &msg, MSG_ERRQUEUE | MSG_DONTWAIT);
if (res < 0)
    goto error;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING)
        memcpy(&tss, CMSG_DATA(cmsg), sizeof(tss));
    else if (cmsg->cmsg_level == SOL_BLUETOOTH && cmsg->cmsg_type == BT_SCM_ERROR)
        memcpy(&serr, CMSG_DATA(cmsg), sizeof(serr));
}
tstamp_clock_realtime = tss.ts[0];
tstamp_type = serr->ee_info;      /* SCM_TSTAMP_SND or SCM_TSTAMP_COMPLETION */
tstamp_seqnum = serr->ee_data;

#include <linux/ethtool.h>
#include <linux/sockios.h>
#include <net/if.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
...
struct ifreq ifr = {};
struct ethtool_ts_info cmd = {};
int sk;
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "hci0");
ifr.ifr_data = (void *)&cmd;
cmd.cmd = ETHTOOL_GET_TS_INFO;
sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP);
if (sk < 0)
    goto error;
if (ioctl(sk, SIOCETHTOOL, &ifr))
    goto error;
sof_available = cmd.so_timestamping;