sctp: Add support to per-association statistics via a new SCTP_GET_ASSOC_STATS call

The current SCTP stack is lacking a mechanism to have per association
statistics. This is an implementation modeled after OpenSolaris'
SCTP_GET_ASSOC_STATS.

Userspace part will follow on lksctp if/when there is a general ACK on
this.
V4:
- Move ipackets++ before q->immediate.func() for consistency reasons
- Move sctp_max_rto() at the end of sctp_transport_update_rto() to avoid
  returning bogus RTO values
- return asoc->rto_min when max_obs_rto value has not changed

V3:
- Increase ictrlchunks in sctp_assoc_bh_rcv() as well
- Move ipackets++ to sctp_inq_push()
- return 0 when no rto updates took place since the last call

V2:
- Implement partial retrieval of stat struct to cope for future expansion
- Kill the rtxpackets counter as it cannot be precise anyway
- Rename outseqtsns to outofseqtsns to make it clearer that these are out
  of sequence unexpected TSNs
- Move asoc->ipackets++ under a lock to avoid potential miscounts
- Fold asoc->opackets++ into the already existing asoc check
- Kill unneeded (q->asoc) test when increasing rtxchunks
- Do not count octrlchunks if sending failed (SCTP_XMIT_OK != 0)
- Don't count SHUTDOWNs as SACKs
- Move SCTP_GET_ASSOC_STATS to the private space API
- Adjust the len check in sctp_getsockopt_assoc_stats() to allow for
  future struct growth
- Move association statistics in their own struct
- Update idupchunks when we send a SACK with dup TSNs
- return min_rto in max_rto when RTO has not changed. Also return the
  transport when max_rto last changed.

Signed-off: Michele Baldessari <michele@acksyn.org>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>

Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/sm_statefuns.c

@@ -6133,6 +6133,8 @@ static int sctp_eat_data(const struct sctp_association *asoc,
 		/* The TSN is too high--silently discard the chunk and
 		 * count on it getting retransmitted later.
 		 */
+		if (chunk->asoc)
+			chunk->asoc->stats.outofseqtsns++;
 		return SCTP_IERROR_HIGH_TSN;
 	} else if (tmp > 0) {
 		/* This is a duplicate.  Record it.  */
@@ -6232,10 +6234,14 @@ static int sctp_eat_data(const struct sctp_association *asoc,
 	/* Note: Some chunks may get overcounted (if we drop) or overcounted
 	 * if we renege and the chunk arrives again.
 	 */
-	if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED)
+	if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED) {
 		SCTP_INC_STATS(net, SCTP_MIB_INUNORDERCHUNKS);
-	else {
+		if (chunk->asoc)
+			chunk->asoc->stats.iuodchunks++;
+	} else {
 		SCTP_INC_STATS(net, SCTP_MIB_INORDERCHUNKS);
+		if (chunk->asoc)
+			chunk->asoc->stats.iodchunks++;
 		ordered = 1;
 	}