libevent 是否支持 netlink 套接字

Question

我使用 netlink 从内核接收中断号。用户空间中的应用程序使用 libevent 来处理 TCP/IP 请求和 netlink 消息。 libevent 是否支持 Linux netlink 套接字？我会很感激一个简单的例子。

Answer 1

是的，libevent 支持 netlink 套接字。

有https://github.com/libevent/libevent/blob/master/sample/hello-world.c，下面修改为监听netlink socket。

基本示例监听 Linux 网络接口的创建/删除，可以使用 sudo 执行以获得所需的权限。它侦听与ip monitor link 相同的事件。

另一个使用 libevent 监听 RAW 套接字的例子是这里https://github.com/bodgit/libevent-natpmp/blob/master/natpmp.c。

static void link_recvmsg(int fd, short event, void *arg)
{
    char          buf[NLMSG_SPACE(BUF_SIZE)] = {0};
    socklen_t     socklen;
    struct iovec  iov = {.iov_base = buf, .iov_len = sizeof(buf)};
    struct sockaddr addr;
    memset(&addr, 0, sizeof(struct sockaddr));

    if (!fd || -1 == fd)
        return;

    int status = getsockname(fd, &addr, &socklen);
    if(-1 == status)
        return;

    struct msghdr mh = {.msg_name = NULL, .msg_namelen = 0, .msg_iov = &iov, .msg_iovlen = 1,
        .msg_flags = 0, .msg_name = &addr, .msg_namelen = sizeof(struct sockaddr)};

    status = recvmsg(fd, &mh, 0);
    if ((-1 == status) && ((EINTR == errno) || (EAGAIN == errno)))
        return;
    if(-1 == status)
        return;
    if ((mh.msg_flags & MSG_TRUNC) == MSG_TRUNC)
        return;
    if ((mh.msg_flags & MSG_CTRUNC) == MSG_CTRUNC)
        return;

    for (const struct nlmsghdr *h = (struct nlmsghdr *)buf; NLMSG_OK(h, status); h = NLMSG_NEXT(h, status)) {
        switch (h->nlmsg_type) {
            case RTM_NEWLINK:
                fprintf(stderr, "got RTM_NEWLINK\n");
                break;
            case RTM_DELLINK:
                fprintf(stderr, "got RTM_DELLINK\n");
                break;
            default:
                fprintf(stderr, "unexpected case in swtch statement\n");
                break;
        }
    }
}
int main(int argc, char **argv)
{
    /* some init code here */
    /* NETLINK socket */
    int status;
    int buf_size = BUF_SIZE; 
    struct sockaddr_nl src_addr;

    int socket_nl = socket(AF_NETLINK, SOCK_RAW | SOCK_NONBLOCK, NETLINK_ROUTE);
    if(-1 == socket_nl) return -1;

    memset(&src_addr, 0, sizeof(struct sockaddr_nl));
    src_addr.nl_family = AF_NETLINK;
    src_addr.nl_pid = getpid();
    src_addr.nl_groups |= RTNLGRP_LINK;

    status = setsockopt(socket_nl, SOL_SOCKET, SO_RCVBUF,
            &buf_size, sizeof(buf_size));
    if(-1 == status) return -1; 

    status = bind(socket_nl, (struct sockaddr *)&src_addr, sizeof(struct sockaddr_nl));
    if(status < 0) return -1;

    static struct event nl_ev;
    event_set(&nl_ev, socket_nl, EV_READ|EV_PERSIST, link_recvmsg,
            NULL);
    if (base) {
        event_base_set(base, &nl_ev);
    }
    event_add(&nl_ev, NULL);
    /* some other code, dispatch event and deinit */
}