sctp: add basic structures and make chunk function for ifwdtsn

sctp_ifwdtsn_skip, sctp_ifwdtsn_hdr and sctp_ifwdtsn_chunk are used to
define and parse I-FWD TSN chunk format, and sctp_make_ifwdtsn is a
function to build the chunk.

The I-FORWARD-TSN Chunk Format is defined in section 2.3.1 of RFC8260.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Marcelo R. Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sctp.h

@@ -110,6 +110,7 @@ enum sctp_cid {
 
 	/* Use hex, as defined in ADDIP sec. 3.1 */
 	SCTP_CID_ASCONF			= 0xC1,
+	SCTP_CID_I_FWD_TSN		= 0xC2,
 	SCTP_CID_ASCONF_ACK		= 0x80,
 	SCTP_CID_RECONF			= 0x82,
 }; /* enum */
@@ -616,6 +617,22 @@ struct sctp_fwdtsn_chunk {
 	struct sctp_fwdtsn_hdr fwdtsn_hdr;
 };
 
+struct sctp_ifwdtsn_skip {
+	__be16 stream;
+	__u8 reserved;
+	__u8 flags;
+	__be32 mid;
+};
+
+struct sctp_ifwdtsn_hdr {
+	__be32 new_cum_tsn;
+	struct sctp_ifwdtsn_skip skip[0];
+};
+
+struct sctp_ifwdtsn_chunk {
+	struct sctp_chunkhdr chunk_hdr;
+	struct sctp_ifwdtsn_hdr fwdtsn_hdr;
+};
 
 /* ADDIP
  * Section 3.1.1 Address Configuration Change Chunk (ASCONF)

include/net/sctp/sm.h

@@ -199,6 +199,9 @@ struct sctp_chunk *sctp_make_cwr(const struct sctp_association *asoc,
 				 const struct sctp_chunk *chunk);
 struct sctp_chunk *sctp_make_idata(const struct sctp_association *asoc,
 				   __u8 flags, int paylen, gfp_t gfp);
+struct sctp_chunk *sctp_make_ifwdtsn(const struct sctp_association *asoc,
+				     __u32 new_cum_tsn, size_t nstreams,
+				     struct sctp_ifwdtsn_skip *skiplist);
 struct sctp_chunk *sctp_make_datafrag_empty(const struct sctp_association *asoc,
 					    const struct sctp_sndrcvinfo *sinfo,
 					    int len, __u8 flags, gfp_t gfp);

include/net/sctp/structs.h

@@ -599,6 +599,7 @@ struct sctp_chunk {
 		struct sctp_fwdtsn_hdr *fwdtsn_hdr;
 		struct sctp_authhdr *auth_hdr;
 		struct sctp_idatahdr *idata_hdr;
+		struct sctp_ifwdtsn_hdr *ifwdtsn_hdr;
 	} subh;
 
 	__u8 *chunk_end;

net/sctp/sm_make_chunk.c

@@ -3536,6 +3536,30 @@ struct sctp_chunk *sctp_make_fwdtsn(const struct sctp_association *asoc,
 	return retval;
 }
 
+struct sctp_chunk *sctp_make_ifwdtsn(const struct sctp_association *asoc,
+				     __u32 new_cum_tsn, size_t nstreams,
+				     struct sctp_ifwdtsn_skip *skiplist)
+{
+	struct sctp_chunk *retval = NULL;
+	struct sctp_ifwdtsn_hdr ftsn_hdr;
+	size_t hint;
+
+	hint = (nstreams + 1) * sizeof(__u32);
+
+	retval = sctp_make_control(asoc, SCTP_CID_I_FWD_TSN, 0, hint,
+				   GFP_ATOMIC);
+	if (!retval)
+		return NULL;
+
+	ftsn_hdr.new_cum_tsn = htonl(new_cum_tsn);
+	retval->subh.ifwdtsn_hdr =
+		sctp_addto_chunk(retval, sizeof(ftsn_hdr), &ftsn_hdr);
+
+	sctp_addto_chunk(retval, nstreams * sizeof(skiplist[0]), skiplist);
+
+	return retval;
+}
+
 /* RE-CONFIG 3.1 (RE-CONFIG chunk)
  *   0                   1                   2                   3
  *   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1