Charge at least one credit, if server says that it supports multicredit

In SMB2.1 and later the server will usually set the large MTU flag, and
we need to charge at least one credit, if server says that since
it supports multicredit.  Windows seems to let us get away with putting
a zero there, but they confirmed that it is wrong and the spec says
to put one there (if the request is under 64K and the CAP_LARGE_MTU
was returned during protocol negotiation by the server.

CC: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/smb2pdu.c

@@ -1,7 +1,7 @@
 /*
  *   fs/cifs/smb2pdu.c
  *
- *   Copyright (C) International Business Machines  Corp., 2009, 2012
+ *   Copyright (C) International Business Machines  Corp., 2009, 2013
  *                 Etersoft, 2012
  *   Author(s): Steve French (sfrench@us.ibm.com)
  *              Pavel Shilovsky (pshilovsky@samba.org) 2012
@@ -108,6 +108,13 @@ smb2_hdr_assemble(struct smb2_hdr *hdr, __le16 smb2_cmd /* command */ ,
 	if (!tcon)
 		goto out;
 
+	/* BB FIXME when we do write > 64K add +1 for every 64K in req or rsp */
+	/* GLOBAL_CAP_LARGE_MTU will only be set if dialect > SMB2.02 */
+	/* See sections 2.2.4 and 3.2.4.1.5 of MS-SMB2 */
+	if (tcon->ses->server->capabilities & SMB2_GLOBAL_CAP_LARGE_MTU)
+		hdr->CreditCharge = cpu_to_le16(1);
+	/* else CreditCharge MBZ */
+
 	hdr->TreeId = tcon->tid;
 	/* Uid is not converted */
 	if (tcon->ses)