+
+ssize_t next_datagram_size_fd(int fd) {
+ ssize_t l;
+ int k;
+
+ /* This is a bit like FIONREAD/SIOCINQ, however a bit more powerful. The difference being: recv(MSG_PEEK) will
+ * actually cause the next datagram in the queue to be validated regarding checksums, which FIONREAD doesn't
+ * do. This difference is actually of major importance as we need to be sure that the size returned here
+ * actually matches what we will read with recvmsg() next, as otherwise we might end up allocating a buffer of
+ * the wrong size. */
+
+ l = recv(fd, NULL, 0, MSG_PEEK|MSG_TRUNC);
+ if (l < 0) {
+ if (errno == EOPNOTSUPP || errno == EFAULT)
+ goto fallback;
+
+ return -errno;
+ }
+ if (l == 0)
+ goto fallback;
+
+ return l;
+
+fallback:
+ k = 0;
+
+ /* Some sockets (AF_PACKET) do not support null-sized recv() with MSG_TRUNC set, let's fall back to FIONREAD
+ * for them. Checksums don't matter for raw sockets anyway, hence this should be fine. */
+
+ if (ioctl(fd, FIONREAD, &k) < 0)
+ return -errno;
+
+ return (ssize_t) k;
+}
+
+int flush_accept(int fd) {
+
+ struct pollfd pollfd = {
+ .fd = fd,
+ .events = POLLIN,
+ };
+ int r;
+
+
+ /* Similar to flush_fd() but flushes all incoming connection by accepting them and immediately closing them. */
+
+ for (;;) {
+ int cfd;
+
+ r = poll(&pollfd, 1, 0);
+ if (r < 0) {
+ if (errno == EINTR)
+ continue;
+
+ return -errno;
+
+ } else if (r == 0)
+ return 0;
+
+ cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
+ if (cfd < 0) {
+ if (errno == EINTR)
+ continue;
+
+ if (errno == EAGAIN)
+ return 0;
+
+ return -errno;
+ }
+
+ close(cfd);
+ }
+}
+#endif // 0
+
+struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t length) {
+ struct cmsghdr *cmsg;
+
+ assert(mh);
+
+ CMSG_FOREACH(cmsg, mh)
+ if (cmsg->cmsg_level == level &&
+ cmsg->cmsg_type == type &&
+ (length == (socklen_t) -1 || length == cmsg->cmsg_len))
+ return cmsg;
+
+ return NULL;
+}
+
+int socket_ioctl_fd(void) {
+ int fd;
+
+ /* Create a socket to invoke the various network interface ioctl()s on. Traditionally only AF_INET was good for
+ * that. Since kernel 4.6 AF_NETLINK works for this too. We first try to use AF_INET hence, but if that's not
+ * available (for example, because it is made unavailable via SECCOMP or such), we'll fall back to the more
+ * generic AF_NETLINK. */
+
+ fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC, 0);
+ if (fd < 0)
+ fd = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_GENERIC);
+ if (fd < 0)
+ return -errno;
+
+ return fd;
+}