net: TX timestamps for IPv6 UDP packets

Enabling TX timestamps (SO_TIMESTAMPING) for IPv6 UDP packets, in
the same fashion as for IPv4. Necessary in order for NICs such as
Intel 82580 to timestamp IPv6 packets.
Signed-off-by: NAnders Berggren <anders@halon.se>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -1118,6 +1118,7 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
 	int err;
 	int offset = 0;
 	int csummode = CHECKSUM_NONE;
+	__u8 tx_flags = 0;
 
 	if (flags&MSG_PROBE)
 		return 0;
@@ -1202,6 +1203,13 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
 		}
 	}
 
+	/* For UDP, check if TX timestamp is enabled */
+	if (sk->sk_type == SOCK_DGRAM) {
+		err = sock_tx_timestamp(sk, &tx_flags);
+		if (err)
+			goto error;
+	}
+
 	/*
 	 * Let's try using as much space as possible.
 	 * Use MTU if total length of the message fits into the MTU.
@@ -1306,6 +1314,12 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
 							   sk->sk_allocation);
 				if (unlikely(skb == NULL))
 					err = -ENOBUFS;
+				else {
+					/* Only the initial fragment
+					 * is time stamped.
+					 */
+					tx_flags = 0;
+				}
 			}
 			if (skb == NULL)
 				goto error;
@@ -1317,6 +1331,9 @@ int ip6_append_data(struct sock *sk, int getfrag(void *from, char *to,
 			/* reserve for fragmentation */
 			skb_reserve(skb, hh_len+sizeof(struct frag_hdr));
 
+			if (sk->sk_type == SOCK_DGRAM)
+				skb_shinfo(skb)->tx_flags = tx_flags;
+
 			/*
 			 *	Find where to start putting bytes
 			 */