[DCCP]: Dedicated auxiliary states to support passive-close

This adds two auxiliary states to deal with passive closes:
  * PASSIVE_CLOSE    (reached from OPEN via reception of Close)    and
  * PASSIVE_CLOSEREQ (reached from OPEN via reception of CloseReq)
as internal intermediate states.

These states are used to allow a receiver to process unread data before
acknowledging the received connection-termination-request (the Close/CloseReq).

Without such support, it will happen that passively-closed sockets enter CLOSED
state while there is still unprocessed data in the queue; leading to unexpected
and erratic API behaviour.

PASSIVE_CLOSE has been mapped into TCPF_CLOSE_WAIT, so that the code will
seamlessly work with inet_accept() (which tests for this state).

The state names are thanks to Arnaldo, who suggested this naming scheme
following an earlier revision of this patch.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/dccp.h

@@ -231,14 +231,35 @@ enum dccp_state {
 	DCCP_REQUESTING	     = TCP_SYN_SENT,
 	DCCP_LISTEN	     = TCP_LISTEN,
 	DCCP_RESPOND	     = TCP_SYN_RECV,
+	/*
+	 * States involved in closing a DCCP connection:
+	 * 1) ACTIVE_CLOSEREQ is entered by a server sending a CloseReq.
+	 *
+	 * 2) CLOSING can have three different meanings (RFC 4340, 8.3):
+	 *  a. Client has performed active-close, has sent a Close to the server
+	 *     from state OPEN or PARTOPEN, and is waiting for the final Reset
+	 *     (in this case, SOCK_DONE == 1).
+	 *  b. Client is asked to perform passive-close, by receiving a CloseReq
+	 *     in (PART)OPEN state. It sends a Close and waits for final Reset
+	 *     (in this case, SOCK_DONE == 0).
+	 *  c. Server performs an active-close as in (a), keeps TIMEWAIT state.
+	 *
+	 * 3) The following intermediate states are employed to give passively
+	 *    closing nodes a chance to process their unread data:
+	 *    - PASSIVE_CLOSE    (from OPEN => CLOSED) and
+	 *    - PASSIVE_CLOSEREQ (from (PART)OPEN to CLOSING; case (b) above).
+	 */
+	DCCP_ACTIVE_CLOSEREQ = TCP_FIN_WAIT1,
+	DCCP_PASSIVE_CLOSE   = TCP_CLOSE_WAIT,	/* any node receiving a Close */
 	DCCP_CLOSING	     = TCP_CLOSING,
 	DCCP_TIME_WAIT	     = TCP_TIME_WAIT,
 	DCCP_CLOSED	     = TCP_CLOSE,
 	DCCP_PARTOPEN	     = TCP_MAX_STATES,
+	DCCP_PASSIVE_CLOSEREQ,			/* clients receiving CloseReq */
 	DCCP_MAX_STATES
 };
 
-#define DCCP_STATE_MASK 0xf
+#define DCCP_STATE_MASK 0x1f
 #define DCCP_ACTION_FIN (1<<7)
 
 enum {
@@ -246,10 +267,11 @@ enum {
 	DCCPF_REQUESTING      = TCPF_SYN_SENT,
 	DCCPF_LISTEN	      = TCPF_LISTEN,
 	DCCPF_RESPOND	      = TCPF_SYN_RECV,
+	DCCPF_ACTIVE_CLOSEREQ = TCPF_FIN_WAIT1,
 	DCCPF_CLOSING	      = TCPF_CLOSING,
 	DCCPF_TIME_WAIT	      = TCPF_TIME_WAIT,
 	DCCPF_CLOSED	      = TCPF_CLOSE,
-	DCCPF_PARTOPEN	 = 1 << DCCP_PARTOPEN,
+	DCCPF_PARTOPEN	      = (1 << DCCP_PARTOPEN),
 };
 
 static inline struct dccp_hdr *dccp_hdr(const struct sk_buff *skb)

net/dccp/proto.c

@@ -60,8 +60,7 @@ void dccp_set_state(struct sock *sk, const int state)
 {
 	const int oldstate = sk->sk_state;
 
-	dccp_pr_debug("%s(%p) %-10.10s -> %s\n",
-		      dccp_role(sk), sk,
+	dccp_pr_debug("%s(%p)  %s  -->  %s\n", dccp_role(sk), sk,
 		      dccp_state_name(oldstate), dccp_state_name(state));
 	WARN_ON(state == oldstate);
 
@@ -140,6 +139,9 @@ const char *dccp_state_name(const int state)
 	[DCCP_LISTEN]		= "LISTEN",
 	[DCCP_RESPOND]		= "RESPOND",
 	[DCCP_CLOSING]		= "CLOSING",
+	[DCCP_ACTIVE_CLOSEREQ]	= "CLOSEREQ",
+	[DCCP_PASSIVE_CLOSE]	= "PASSIVE_CLOSE",
+	[DCCP_PASSIVE_CLOSEREQ]	= "PASSIVE_CLOSEREQ",
 	[DCCP_TIME_WAIT]	= "TIME_WAIT",
 	[DCCP_CLOSED]		= "CLOSED",
 	};