sctp: add support for PR-SCTP Information for sendmsg

This patch is to add support for PR-SCTP Information for sendmsg,
as described in section 5.3.7 of RFC6458.

With this option, you can specify pr_policy and pr_value for user
data in sendmsg.

It's also a necessary send info for sctp_sendv.

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>
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 03e92dd..d40a2a3 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -2112,6 +2112,7 @@ struct sctp_cmsgs {
 	struct sctp_initmsg *init;
 	struct sctp_sndrcvinfo *srinfo;
 	struct sctp_sndinfo *sinfo;
+	struct sctp_prinfo *prinfo;
 };
 
 /* Structure for tracking memory objects */
diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
index 4c4db14..0dd1f82 100644
--- a/include/uapi/linux/sctp.h
+++ b/include/uapi/linux/sctp.h
@@ -260,6 +260,19 @@ struct sctp_nxtinfo {
 	sctp_assoc_t nxt_assoc_id;
 };
 
+/* 5.3.7 SCTP PR-SCTP Information Structure (SCTP_PRINFO)
+ *
+ *   This cmsghdr structure specifies SCTP options for sendmsg().
+ *
+ *   cmsg_level    cmsg_type      cmsg_data[]
+ *   ------------  ------------   -------------------
+ *   IPPROTO_SCTP  SCTP_PRINFO    struct sctp_prinfo
+ */
+struct sctp_prinfo {
+	__u16 pr_policy;
+	__u32 pr_value;
+};
+
 /*
  *  sinfo_flags: 16 bits (unsigned integer)
  *
@@ -293,6 +306,8 @@ typedef enum sctp_cmsg_type {
 #define SCTP_RCVINFO	SCTP_RCVINFO
 	SCTP_NXTINFO,		/* 5.3.6 SCTP Next Receive Information Structure */
 #define SCTP_NXTINFO	SCTP_NXTINFO
+	SCTP_PRINFO,		/* 5.3.7 SCTP PR-SCTP Information Structure */
+#define SCTP_PRINFO	SCTP_PRINFO
 } sctp_cmsg_t;
 
 /*