netdev - [PATCH net-next] sctp: Add partially support for MSG

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1725FB90@AcuExch.aculab.com>
Date:	Fri, 20 Jun 2014 16:24:57 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: [PATCH net-next] sctp: Add partially support for MSG_MORE to SCTP.

If MSG_MORE is set then buffer sends as if Nagle were enabled.
The first data chunk is still sent on its own, but subsequent chunks
will be bundled and full packets sent.
Full MSG_MORE support would require a timeout (preferably configurable
per-socket) to send the last chunk(s), instead of sending them
when there is nothing outstanding.

Signed-off-by: David Laight <david.laight@...lab.com>
---
 net/sctp/output.c |  7 ++++++-
 net/sctp/socket.c | 14 +++++++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/net/sctp/output.c b/net/sctp/output.c
index 0f4d15f..9486229 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -690,8 +690,13 @@ static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
 	 * Inhibit the sending of new chunks when new outgoing data arrives
 	 * if any previously transmitted data on the connection remains
 	 * unacknowledged.
+	 * If nodelay is clear or MSG_MORE is set then perform the Nagle delay.
+	 * (MSG_MORE from the last sendmsg is saved as 'nodelay & 2'.)
+	 * This is a partial implementation of MSG_MORE since MSG_MORE should
+	 * also delay the first packet. However that would need a timeout be
+	 * added to force the data to be finally sent.
 	 */
-	if (!sctp_sk(asoc->base.sk)->nodelay && sctp_packet_empty(packet) &&
+	if (sctp_sk(asoc->base.sk)->nodelay != 1 && sctp_packet_empty(packet) &&
 	    inflight && sctp_state(asoc, ESTABLISHED)) {
 		unsigned int max = transport->pathmtu - packet->overhead;
 		unsigned int len = chunk->skb->len + q->out_qlen;
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index fee06b9..484c34e 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1927,6 +1927,18 @@ static int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
 		pr_debug("%s: we associated primitively\n", __func__);
 	}
 
+	/* Setting MSG_MORE currently has the same effect as enabling Nagle.
+	 * This means that the user can't force bundling of the first two data
+	 * chunks.  It does mean that all the data chunks will be sent
+	 * without an extra timer.
+	 * It is enough to save the last value since any data sent with
+	 * MSG_MORE clear will already have been sent (subject to flow control).
+	 */
+	if (msg->msg_flags & MSG_MORE)
+		sp->nodelay |= 2;
+	else
+		sp->nodelay &= ~2;
+
 	/* Break the message into multiple chunks of maximum size. */
 	datamsg = sctp_datamsg_from_user(asoc, sinfo, msg, msg_len);
 	if (IS_ERR(datamsg)) {
@@ -5020,7 +5032,7 @@ static int sctp_getsockopt_nodelay(struct sock *sk, int len,
 		return -EINVAL;
 
 	len = sizeof(int);
-	val = (sctp_sk(sk)->nodelay == 1);
+	val = sctp_sk(sk)->nodelay & 1;
 	if (put_user(len, optlen))
 		return -EFAULT;
 	if (copy_to_user(optval, &val, len))
-- 
1.8.1.2



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