OpenBSD sendsyslogd example taken from https://github.com/syslog-ng/syslog-ng/issues/1786#issuecomment-348819466

sendsyslogd.c

/* 
https://github.com/syslog-ng/syslog-ng/issues/1786#issuecomment-348819466
*/
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>

#include <syslog.h>

struct NewSyslogListener
{
        int klog;
        int pair[2];
};

int newsysloglistener_init(struct NewSyslogListener *this)
{
        if (socketpair(AF_UNIX, SOCK_DGRAM, PF_UNSPEC, this->pair) == -1) {
                printf("cannot bind socket fd\n");
                return 1;
        }
        if ((this->klog = open("/dev/klog", O_RDONLY, 0)) == -1) {
                printf("cannot open /dev/klog %d\n",errno);
                return 2;
        }

        if (ioctl(this->klog, LIOCSFD, &(this->pair[1])) == -1) {
                printf("cannot ioctl klog LIOCSFD\n");
                return 3;
        }

        close(this->pair[1]);

        return 0;
};

void newsysloglistener_deinit(struct NewSyslogListener *this)
{
        close(this->pair[0]);
        close(this->klog);
}

int main()
{
        struct NewSyslogListener newsyslog;
        int res = -1;

        res = newsysloglistener_init(&newsyslog);
        if (res) {
                return res;
        }

        struct sockaddr_un sa;
        socklen_t          salen;
        ssize_t            n;
        char               linebuf[1025];

        salen = sizeof(sa);

        while (1) {
                n = recvfrom(newsyslog.pair[0], linebuf, 1024, 0, (struct sockaddr*)&sa, &salen);
                if (n>0) printf("msg: %.*s\n", (int)n, linebuf);
                else printf("nothing to print\n");
        };

        newsysloglistener_deinit(&newsyslog);


        return 0;
};