net-timestamp: extend SCM_TIMESTAMPING ancillary data struct

Applications that request kernel tx timestamps with SO_TIMESTAMPING
read timestamps as recvmsg() ancillary data. The response is defined
implicitly as timespec[3].

1) define struct scm_timestamping explicitly and

2) add support for new tstamp types. On tx, scm_timestamping always
   accompanies a sock_extended_err. Define previously unused field
   ee_info to signal the type of ts[0]. Introduce SCM_TSTAMP_SND to
   define the existing behavior.

The reception path is not modified. On rx, no struct similar to
sock_extended_err is passed along with SCM_TIMESTAMPING.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index d8222c0..dc0cc5d 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -106,6 +106,7 @@
 #include <linux/sockios.h>
 #include <linux/atalk.h>
 #include <net/busy_poll.h>
+#include <linux/errqueue.h>
 
 #ifdef CONFIG_NET_RX_BUSY_POLL
 unsigned int sysctl_net_busy_read __read_mostly;
@@ -697,7 +698,7 @@
 	struct sk_buff *skb)
 {
 	int need_software_tstamp = sock_flag(sk, SOCK_RCVTSTAMP);
-	struct timespec ts[3];
+	struct scm_timestamping tss;
 	int empty = 1;
 	struct skb_shared_hwtstamps *shhwtstamps =
 		skb_hwtstamps(skb);
@@ -714,24 +715,25 @@
 			put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMP,
 				 sizeof(tv), &tv);
 		} else {
-			skb_get_timestampns(skb, &ts[0]);
+			struct timespec ts;
+			skb_get_timestampns(skb, &ts);
 			put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMPNS,
-				 sizeof(ts[0]), &ts[0]);
+				 sizeof(ts), &ts);
 		}
 	}
 
-
-	memset(ts, 0, sizeof(ts));
-	if (sock_flag(sk, SOCK_TIMESTAMPING_SOFTWARE) &&
-	    ktime_to_timespec_cond(skb->tstamp, ts + 0))
+	memset(&tss, 0, sizeof(tss));
+	if ((sock_flag(sk, SOCK_TIMESTAMPING_SOFTWARE) ||
+	     skb_shinfo(skb)->tx_flags & SKBTX_ANY_SW_TSTAMP) &&
+	    ktime_to_timespec_cond(skb->tstamp, tss.ts + 0))
 		empty = 0;
 	if (shhwtstamps &&
 	    sock_flag(sk, SOCK_TIMESTAMPING_RAW_HARDWARE) &&
-	    ktime_to_timespec_cond(shhwtstamps->hwtstamp, ts + 2))
+	    ktime_to_timespec_cond(shhwtstamps->hwtstamp, tss.ts + 2))
 		empty = 0;
 	if (!empty)
 		put_cmsg(msg, SOL_SOCKET,
-			 SCM_TIMESTAMPING, sizeof(ts), &ts);
+			 SCM_TIMESTAMPING, sizeof(tss), &tss);
 }
 EXPORT_SYMBOL_GPL(__sock_recv_timestamp);