Em Thu, Jul 12, 2007 at 03:23:39PM +0100, Gerrit Renker escreveu: > [DCCP]: Dedicated auxiliary states to support passive-close > > This adds two auxiliary states to deal with passive closes: > * PASSIVE_1 (reached from OPEN via reception of Close) and > * PASSIVE_2 (reached from OPEN via reception of CloseReq) Perhaps we should rename PASSIVE_1 (magic number) to PASSIVE_CLOSEREQ and PASSIVE_2 to PASSIVE_CLOSE, and also CLOSEREQ to ACTIVE_CLOSEREQ? I'll defer these patches till we get some more discussion. There are many more unrelated patches to work on after all :) - Arnaldo > to the internal state machine. > > The PASSIVE_1 and PASSIVE_2 states represent the two ways a passive-close > can happen in DCCP. The addition of these states is not merely to > increase clarity. These states are required by the implementation to > allow a receiver to process unread data before acknowledging the received > connection-termination-request (i.e. the Close/CloseReq). > > Fix: > ---- > This patch uses the PASSIVE_1 and PASSIVE_2 states to explicitly refer to > passive-closing states and to protect against external wipeout of internal > receive queues. The macroscopic behaviour is compatible with RFC 4340, but > without the auxiliary states, buggy, absurd and abnormal behaviour of the > socket API will continue. Which is to say, without auxiliary states it does > not work. > > As a consequence, the count of DCCP_STATE_MASK has been increased, to account > for the number of new states. > > > Implementation Note: > -------------------- > To keep compatibility with sk_stream_wait_connect(): > * DCCP_CLOSING continues to map into TCP_CLOSING (since this state can be > either passive- or active-close) > * DCCP_CLOSEREQ maps into TCP_FIN_WAIT1 (since it is always active-close) > > It is tempting to keep the clever merge of the CLOSEREQ and CLOSING states. > However, with the number of possible state transitions, this would require: > > * quite a number of `if' statements to distinguish all predecessors of > the CLOSING state (server/client, active/passive, server timewait yes/no); > > * two different branches from the CLOSING state: > - to TIMEWAIT if it is not an active server-close without keeping timewait state > - to CLOSED otherwise (and requiring to receive a Close instead of a Reset). > > In light of this, I think it is cleaner to implement separate CLOSEREQ and CLOSING > states (this is done by the subsequent patches). > > Further documentation is on http://www.erg.abdn.ac.uk/users/gerrit/dccp/docs/closing_states/ > > > Why this is necessary [can be removed] > -------------------------------------- > > The two states are not mentioned in the DCCP specification [RFC 4340, 8.4]. > In fact, RFC 4340 is silent about passive-close. In a nutshell, suppose that > the CLOSE_WAIT and LAST_ACK states were removed from TCP, i.e. a FIN triggers > direct transition from ESTABLISHED to CLOSED - similar problem. > The detailed account is as follows. > > The first problem lies in using inet_stream_connect(): > > An absurd case arises if we let the protocol machinery, not the application, > go through the states. If the protocol machinery allows to proceed to DCCP_CLOSED > (which corresponds to TCP_CLOSE), connect() returns with -ECONNABORTED, even if > there was data in the receive queue. > > Therefore, if we want to keep the useful abstraction of inet_stream_connect(), we > need to make sure that a passive close can not lead to DCCP_CLOSE via the protocol > machinery alone. > > The second problem is also related to entering DCCP_CLOSED too early: > > Even if connect() were fixed, if a passive-close can directly trigger a state > transition from OPEN to DCCP_CLOSED, the receiver may not be able to read data > from its input queue. The reason is that the input queue has already been wiped, > DCCP_CLOSED state has been entered, while the SOCK_DONE flag has not yet been set. > Consequently, any subsequent call to dccp_recvmsg terminates in -ENOTCONN, > and this despite of a potentially full receive queue. > > > Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx> > --- > include/linux/dccp.h | 22 +++++++++++++++++++++- > net/dccp/proto.c | 3 +++ > 2 files changed, 24 insertions(+), 1 deletion(-) > > --- a/include/linux/dccp.h > +++ b/include/linux/dccp.h > @@ -230,16 +230,35 @@ enum dccp_state { > DCCP_REQUESTING = TCP_SYN_SENT, > DCCP_LISTEN = TCP_LISTEN, > DCCP_RESPOND = TCP_SYN_RECV, > + /* > + * Close states: > + * > + * CLOSEREQ is active-server close only. > + * CLOSING can have three different meanings [RFC 4340, 8.3]: > + * a. Client has performed active-close, sent a Close to peer from > + * state OPEN or PARTOPEN, waiting for the final Reset > + * (in this case, SOCK_DONE == 1). > + * b. Client performs passive-Close, by receiving an CloseReq in OPEN > + * or PARTOPEN state. It sends a Close and waits for final Reset > + * (in this case, SOCK_DONE == 0). > + * c. Server decides to hold TIMEWAIT state & performs an active-close. > + * To avoid erasing receive queues too early, the transitional states > + * PASSIVE_1 (from OPEN => CLOSED) and PASSIVE_2 (from (PART)OPEN to > + * CLOSING, corresponds to (b) above) are used. > + */ > + DCCP_CLOSEREQ = TCP_FIN_WAIT1, > DCCP_CLOSING = TCP_CLOSING, > DCCP_TIME_WAIT = TCP_TIME_WAIT, > DCCP_CLOSED = TCP_CLOSE, > /* Everything below here is specific to DCCP only */ > DCCP_INTRINSICS = TCP_MAX_STATES, > DCCP_PARTOPEN, > + DCCP_PASSIVE_1, /* any node receiving a Close */ > + DCCP_PASSIVE_2, /* client receiving a CloseReq */ > DCCP_MAX_STATES > }; > > -#define DCCP_STATE_MASK 0xf > +#define DCCP_STATE_MASK 0x1f > #define DCCP_ACTION_FIN (1<<7) > > enum { > @@ -247,6 +266,7 @@ enum { > DCCPF_REQUESTING = TCPF_SYN_SENT, > DCCPF_LISTEN = TCPF_LISTEN, > DCCPF_RESPOND = TCPF_SYN_RECV, > + DCCPF_CLOSEREQ = TCPF_FIN_WAIT1, > DCCPF_CLOSING = TCPF_CLOSING, > DCCPF_TIME_WAIT = TCPF_TIME_WAIT, > DCCPF_CLOSED = TCPF_CLOSE, > --- a/net/dccp/proto.c > +++ b/net/dccp/proto.c > @@ -139,6 +139,9 @@ const char *dccp_state_name(const int st > [DCCP_LISTEN] = "LISTEN", > [DCCP_RESPOND] = "RESPOND", > [DCCP_CLOSING] = "CLOSING", > + [DCCP_CLOSEREQ] = "CLOSEREQ", > + [DCCP_PASSIVE_1] = "PASSIVE_1", > + [DCCP_PASSIVE_2] = "PASSIVE_2", > [DCCP_TIME_WAIT] = "TIME_WAIT", > [DCCP_CLOSED] = "CLOSED", > }; > - > To unsubscribe from this list: send the line "unsubscribe dccp" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
