[X25]: Fast select with no restriction on response

This patch is a follow up to patch 1 regarding "Selective Sub Address
matching with call user data".  It allows use of the Fast-Select-Acceptance
optional user facility for X.25.

This patch just implements fast select with no restriction on response
(NRR).  What this means (according to ITU-T Recomendation 10/96 section
6.16) is that if in an incoming call packet, the relevant facility bits are
set for fast-select-NRR, then the called DTE can issue a direct response to
the incoming packet using a call-accepted packet that contains
call-user-data.  This patch allows such a response.  

The called DTE can also respond with a clear-request packet that contains
call-user-data.  However, this feature is currently not implemented by the
patch.

How is Fast Select Acceptance used?
By default, the system does not allow fast select acceptance (as before).
To enable a response to fast select acceptance,  
After a listen socket in created and bound as follows
	socket(AF_X25, SOCK_SEQPACKET, 0);
	bind(call_soc, (struct sockaddr *)&locl_addr, sizeof(locl_addr));
but before a listen system call is made, the following ioctl should be used.
	ioctl(call_soc,SIOCX25CALLACCPTAPPRV);
Now the listen system call can be made
	listen(call_soc, 4);
After this, an incoming-call packet will be accepted, but no call-accepted 
packet will be sent back until the following system call is made on the socket
that accepts the call
	ioctl(vc_soc,SIOCX25SENDCALLACCPT);
The network (or cisco xot router used for testing here) will allow the 
application server's call-user-data in the call-accepted packet, 
provided the call-request was made with Fast-select NRR.

Signed-off-by: Shaun Pereira <spereira@tusc.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 5 deletions

diff --git a/net/x25/x25_subr.c b/net/x25/x25_subr.c
index c349bbd6168..7fd872ad0c2 100644
--- a/net/x25/x25_subr.c
+++ b/net/x25/x25_subr.c
@@ -19,6 +19,8 @@
  *      mar/20/00       Daniela Squassoni Disabling/enabling of facilities
  *                                        negotiation.
  *      jun/24/01       Arnaldo C. Melo   use skb_queue_purge, cleanups
+ *      apr/04/15       Shaun Pereira           Fast select with no
+ *                                              restriction on response.
  */
 
 #include <linux/kernel.h>
@@ -127,8 +129,12 @@ void x25_write_internal(struct sock *sk, int frametype)
                         len += 1 + X25_ADDR_LEN + X25_MAX_FAC_LEN +
                                X25_MAX_CUD_LEN;
                         break;
-                case X25_CALL_ACCEPTED:
-                        len += 1 + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
+                case X25_CALL_ACCEPTED: /* fast sel with no restr on resp */
+                        if(x25->facilities.reverse & 0x80) {
+                                len += 1 + X25_MAX_FAC_LEN + X25_MAX_CUD_LEN;
+                        } else {
+                                len += 1 + X25_MAX_FAC_LEN;
+                        }
                         break;
                 case X25_CLEAR_REQUEST:
                 case X25_RESET_REQUEST:
@@ -203,9 +209,16 @@ void x25_write_internal(struct sock *sk, int frametype)
                                                         x25->vc_facil_mask);
                         dptr    = skb_put(skb, len);
                         memcpy(dptr, facilities, len);
-                        dptr = skb_put(skb, x25->calluserdata.cudlength);
-                        memcpy(dptr, x25->calluserdata.cuddata,
-                               x25->calluserdata.cudlength);
+
+                        /* fast select with no restriction on response
+                                allows call user data. Userland must
+                                ensure it is ours and not theirs */
+                        if(x25->facilities.reverse & 0x80) {
+                                dptr = skb_put(skb,
+                                        x25->calluserdata.cudlength);
+                                memcpy(dptr, x25->calluserdata.cuddata,
+                                       x25->calluserdata.cudlength);
+                        }
                         x25->calluserdata.cudlength = 0;
                         break;