cifs: cork the socket before a send and uncork it afterward

We want to send SMBs as "atomically" as possible. Prior to sending any
data on the socket, cork it to make sure that no non-full frames go
out. Afterward, uncork it to make sure all of the data gets pushed out
to the wire.

Note that this more or less renders the socket=TCP_NODELAY mount option
obsolete. When TCP_CORK and TCP_NODELAY are used on the same socket,
TCP_NODELAY is essentially ignored.

Acked-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/connect.c

@@ -1680,6 +1680,10 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
 			if (string == NULL)
 				goto out_nomem;
 
+			/*
+			 * FIXME: since we now cork/uncork the socket while
+			 * 	  sending, should we deprecate this option?
+			 */
 			if (strnicmp(string, "TCP_NODELAY", 11) == 0)
 				vol->sockopt_tcp_nodelay = 1;
 			break;

fs/cifs/transport.c

@@ -27,6 +27,7 @@
 #include <linux/net.h>
 #include <linux/delay.h>
 #include <linux/freezer.h>
+#include <linux/tcp.h>
 #include <asm/uaccess.h>
 #include <asm/processor.h>
 #include <linux/mempool.h>
@@ -247,12 +248,23 @@ smb_send_rqst(struct TCP_Server_Info *server, struct smb_rqst *rqst)
 	int n_vec = rqst->rq_nvec;
 	unsigned int smb_buf_length = get_rfc1002_length(iov[0].iov_base);
 	size_t total_len;
+	struct socket *ssocket = server->ssocket;
+	int val = 1;
 
 	cFYI(1, "Sending smb: smb_len=%u", smb_buf_length);
 	dump_smb(iov[0].iov_base, iov[0].iov_len);
 
+	/* cork the socket */
+	kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,
+				(char *)&val, sizeof(val));
+
 	rc = smb_send_kvec(server, iov, n_vec, &total_len);
 
+	/* uncork it */
+	val = 0;
+	kernel_setsockopt(ssocket, SOL_TCP, TCP_CORK,
+				(char *)&val, sizeof(val));
+
 	if ((total_len > 0) && (total_len != smb_buf_length + 4)) {
 		cFYI(1, "partial send (wanted=%u sent=%zu): terminating "
 			"session", smb_buf_length + 4, total_len);