netdev - [PATCH net-next v2 3/3] net: sctp: Add partial support for MSG

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Date:	Wed, 9 Jul 2014 08:29:21 +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>
CC:	"'davem@...emloft.net'" <davem@...emloft.net>
Subject: [PATCH net-next v2 3/3] net: sctp: Add partial support for MSG_MORE
 on 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 timout (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>
---
 include/net/sctp/structs.h |  6 +++++-
 net/sctp/output.c          | 12 ++++++++++--
 net/sctp/socket.c          | 18 +++++++++++++++---
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 0dfcc92..629346f 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -209,7 +209,11 @@ struct sctp_sock {
 	struct sctp_assocparams assocparams;
 	int user_frag;
 	__u32 autoclose;
-	__u8 nodelay;
+
+#define	SCTP_F_TX_NODELAY	0
+#define	SCTP_F_TX_NAGLE		1	/* SCTP_NODELAY not set */
+#define	SCTP_F_TX_MSG_MORE	2	/* MSG_MORE set on last send */
+	__u8 tx_delay;
 	__u8 disable_fragments;
 	__u8 v4mapped;
 	__u8 frag_interleave;
diff --git a/net/sctp/output.c b/net/sctp/output.c
index 7f28a8e..df7889c 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -679,14 +679,22 @@ static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
 	    flight_size >= transport->cwnd)
 		return SCTP_XMIT_RWND_FULL;
 
+	/* If MSG_MORE is set we probably shouldn't create a new message.
+	 * However unless we also implement a timeout (preferable settable
+	 * as a socket option) then data could easily be left unsent.
+	 * Instead we ignore MSG_MORE on the first data chunk.
+	 * This makes the implementation of MSG_MORE the same as the
+	 * implementation of Nagle.
+	 */
+
 	/* Nagle's algorithm to solve small-packet problem:
 	 * Inhibit the sending of new chunks when new outgoing data arrives
 	 * if any previously transmitted data on the connection remains
 	 * unacknowledged.
 	 */
 
-	if (sctp_sk(asoc->base.sk)->nodelay)
-		/* Nagle disabled */
+	if (sctp_sk(asoc->base.sk)->tx_delay == SCTP_F_TX_NODELAY)
+		/* Nagle disabled and MSG_MORE unset */
 		return SCTP_XMIT_OK;
 
 	if (!sctp_packet_empty(packet))
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index fee06b9..4a9f760 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->tx_delay |= SCTP_F_TX_MSG_MORE;
+	else
+		sp->tx_delay &= ~SCTP_F_TX_MSG_MORE;
+
 	/* Break the message into multiple chunks of maximum size. */
 	datamsg = sctp_datamsg_from_user(asoc, sinfo, msg, msg_len);
 	if (IS_ERR(datamsg)) {
@@ -2821,7 +2833,7 @@ static int sctp_setsockopt_nodelay(struct sock *sk, char __user *optval,
 	if (get_user(val, (int __user *)optval))
 		return -EFAULT;
 
-	sctp_sk(sk)->nodelay = (val == 0) ? 0 : 1;
+	sctp_sk(sk)->tx_delay = val == 0 ? SCTP_F_TX_NAGLE : SCTP_F_TX_NODELAY;
 	return 0;
 }
 
@@ -3968,7 +3980,7 @@ static int sctp_init_sock(struct sock *sk)
 	sp->disable_fragments = 0;
 
 	/* Enable Nagle algorithm by default.  */
-	sp->nodelay           = 0;
+	sp->tx_delay          = SCTP_F_TX_NAGLE;
 
 	/* Enable by default. */
 	sp->v4mapped          = 1;
@@ -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)->tx_delay & SCTP_F_TX_NAGLE ? 0 : 1;
 	if (put_user(len, optlen))
 		return -EFAULT;
 	if (copy_to_user(optval, &val, len))
-- 
1.8.1.2



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