sctp: implement the sender side for SACK-IMMEDIATELY extension

This patch implement the sender side for SACK-IMMEDIATELY
extension.

  Section 4.1.  Sender Side Considerations

  Whenever the sender of a DATA chunk can benefit from the
  corresponding SACK chunk being sent back without delay, the sender
  MAY set the I-bit in the DATA chunk header.

  Reasons for setting the I-bit include

  o  The sender is in the SHUTDOWN-PENDING state.

  o  The application requests to set the I-bit of the last DATA chunk
     of a user message when providing the user message to the SCTP
     implementation.
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: NVlad Yasevich <vladislav.yasevich@hp.com>

include/net/sctp/user.h

@@ -206,6 +206,7 @@ enum sctp_sinfo_flags {
 	SCTP_UNORDERED = 1,  /* Send/receive message unordered. */
 	SCTP_ADDR_OVER = 2,  /* Override the primary destination. */
 	SCTP_ABORT=4,        /* Send an ABORT message to the peer. */
+	SCTP_SACK_IMMEDIATELY = 8,	/* SACK should be sent without delay */
 	SCTP_EOF=MSG_FIN,    /* Initiate graceful shutdown process. */	
 };
 

net/sctp/chunk.c

@@ -263,9 +263,18 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 		if (0 == i)
 			frag |= SCTP_DATA_FIRST_FRAG;
 
-		if ((i == (whole - 1)) && !over)
+		if ((i == (whole - 1)) && !over) {
 			frag |= SCTP_DATA_LAST_FRAG;
 
+			/* The application requests to set the I-bit of the
+			 * last DATA chunk of a user message when providing
+			 * the user message to the SCTP implementation.
+			 */
+			if ((sinfo->sinfo_flags & SCTP_EOF) ||
+			    (sinfo->sinfo_flags & SCTP_SACK_IMMEDIATELY))
+				frag |= SCTP_DATA_SACK_IMM;
+		}
+
 		chunk = sctp_make_datafrag_empty(asoc, sinfo, len, frag, 0);
 
 		if (!chunk)
@@ -297,6 +306,10 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
 		else
 			frag = SCTP_DATA_LAST_FRAG;
 
+		if ((sinfo->sinfo_flags & SCTP_EOF) ||
+		    (sinfo->sinfo_flags & SCTP_SACK_IMMEDIATELY))
+			frag |= SCTP_DATA_SACK_IMM;
+
 		chunk = sctp_make_datafrag_empty(asoc, sinfo, over, frag, 0);
 
 		if (!chunk)

net/sctp/outqueue.c

@@ -1011,6 +1011,13 @@ static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
 				break;
 
 			case SCTP_XMIT_OK:
+				/* The sender is in the SHUTDOWN-PENDING state,
+				 * The sender MAY set the I-bit in the DATA
+				 * chunk header.
+				 */
+				if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING)
+					chunk->chunk_hdr->flags |= SCTP_DATA_SACK_IMM;
+
 				break;
 
 			default: