[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>

1 files changed, 39 insertions, 17 deletions

diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index a0073268808f..8b3f9ad3cf04 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -227,29 +227,51 @@ struct dccp_so_feat {
 #include <net/tcp_states.h>
 
 enum dccp_state {
-        DCCP_OPEN       = TCP_ESTABLISHED,
-        DCCP_REQUESTING = TCP_SYN_SENT,
-        DCCP_LISTEN     = TCP_LISTEN,
-        DCCP_RESPOND    = TCP_SYN_RECV,
-        DCCP_CLOSING    = TCP_CLOSING,
-        DCCP_TIME_WAIT  = TCP_TIME_WAIT,
-        DCCP_CLOSED     = TCP_CLOSE,
-        DCCP_PARTOPEN   = TCP_MAX_STATES,
+        DCCP_OPEN            = TCP_ESTABLISHED,
+        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 {
-        DCCPF_OPEN       = TCPF_ESTABLISHED,
-        DCCPF_REQUESTING = TCPF_SYN_SENT,
-        DCCPF_LISTEN     = TCPF_LISTEN,
-        DCCPF_RESPOND    = TCPF_SYN_RECV,
-        DCCPF_CLOSING    = TCPF_CLOSING,
-        DCCPF_TIME_WAIT  = TCPF_TIME_WAIT,
-        DCCPF_CLOSED     = TCPF_CLOSE,
-        DCCPF_PARTOPEN   = 1 << DCCP_PARTOPEN,
+        DCCPF_OPEN            = TCPF_ESTABLISHED,
+        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),
 };
 
 static inline struct dccp_hdr *dccp_hdr(const struct sk_buff *skb)