sctp: add the constants/variables and states and some APIs for transport

These are 4 constants described in rfc8899#section-5.1.2:

  MAX_PROBES, MIN_PLPMTU, MAX_PLPMTU, BASE_PLPMTU;

And 2 variables described in rfc8899#section-5.1.3:

  PROBED_SIZE, PROBE_COUNT;

And 5 states described in rfc8899#section-5.2:

  DISABLED, BASE, SEARCH, SEARCH_COMPLETE, ERROR;

And these 4 APIs are used to reset/update PLPMTUD, check if PLPMTUD is
enabled, and calculate the additional headers length for a transport.

Note the member 'probe_high' in transport will be set to the probe
size when a probe fails with this probe size in the next patches.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index bf5d22deaefb..85d3566c2227 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -978,6 +978,14 @@ struct sctp_transport {
 		char cacc_saw_newack;
 	} cacc;
 
+	struct {
+		__u16 pmtu;
+		__u16 probe_size;
+		__u16 probe_high;
+		__u8 probe_count;
+		__u8 state;
+	} pl; /* plpmtud related */
+
 	/* 64-bit random number sent with heartbeat. */
 	__u64 hb_nonce;