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>

include/net/sctp/structs.h

@@ -1312,6 +1312,40 @@ struct sctp_inithdr_host {
 	__u32 initial_tsn;
 };
 
+/* SCTP_GET_ASSOC_STATS counters */
+struct sctp_priv_assoc_stats {
+	/* Maximum observed rto in the association during subsequent
+	 * observations. Value is set to 0 if no RTO measurement took place
+	 * The transport where the max_rto was observed is returned in
+	 * obs_rto_ipaddr
+	 */
+	struct sockaddr_storage obs_rto_ipaddr;
+	__u64 max_obs_rto;
+	/* Total In and Out SACKs received and sent */
+	__u64 isacks;
+	__u64 osacks;
+	/* Total In and Out packets received and sent */
+	__u64 opackets;
+	__u64 ipackets;
+	/* Total retransmitted chunks */
+	__u64 rtxchunks;
+	/* TSN received > next expected */
+	__u64 outofseqtsns;
+	/* Duplicate Chunks received */
+	__u64 idupchunks;
+	/* Gap Ack Blocks received */
+	__u64 gapcnt;
+	/* Unordered data chunks sent and received */
+	__u64 ouodchunks;
+	__u64 iuodchunks;
+	/* Ordered data chunks sent and received */
+	__u64 oodchunks;
+	__u64 iodchunks;
+	/* Control chunks sent and received */
+	__u64 octrlchunks;
+	__u64 ictrlchunks;
+};
+
 /* RFC2960
  *
  * 12. Recommended Transmission Control Block (TCB) Parameters
@@ -1830,6 +1864,8 @@ struct sctp_association {
 
 	__u8 need_ecne:1,	/* Need to send an ECNE Chunk? */
 	     temp:1;		/* Is it a temporary association? */
+
+	struct sctp_priv_assoc_stats stats;
 };