+/**
+ * udp_poll - wait for a UDP event.
+ * @file - file struct
+ * @sock - socket
+ * @wait - poll table
+ *
+ * This is same as datagram poll, except for the special case of
+ * blocking sockets. If application is using a blocking fd
+ * and a packet with checksum error is in the queue;
+ * then it could get return from select indicating data available
+ * but then block when reading it. Add special case code
+ * to work around these arguably broken applications.
+ */
+unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
+{
+ unsigned int mask = datagram_poll(file, sock, wait);
+ struct sock *sk = sock->sk;
+
+ /* Check for false positives due to checksum errors */
+ if ( (mask & POLLRDNORM) &&
+ !(file->f_flags & O_NONBLOCK) &&
+ !(sk->sk_shutdown & RCV_SHUTDOWN)){
+ struct sk_buff_head *rcvq = &sk->sk_receive_queue;
+ struct sk_buff *skb;
+
+ spin_lock_irq(&rcvq->lock);
+ while ((skb = skb_peek(rcvq)) != NULL) {
+ if (udp_checksum_complete(skb)) {
+ UDP_INC_STATS_BH(UDP_MIB_INERRORS);
+ __skb_unlink(skb, rcvq);
+ kfree_skb(skb);
+ } else {
+ skb->ip_summed = CHECKSUM_UNNECESSARY;
+ break;
+ }
+ }
+ spin_unlock_irq(&rcvq->lock);
+
+ /* nothing to see, move along */
+ if (skb == NULL)
+ mask &= ~(POLLIN | POLLRDNORM);
+ }
+
+ return mask;
+
+}