5 The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
6 that can be used to perform RxRPC remote operations. This is done over sockets
7 of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and
8 receive data, aborts and errors.
10 Contents of this document:
14 (*) RxRPC protocol summary.
16 (*) AF_RXRPC driver model.
24 (*) Example client usage.
26 (*) Example server usage.
28 (*) AF_RXRPC kernel interface.
35 RxRPC is a two-layer protocol. There is a session layer which provides
36 reliable virtual connections using UDP over IPv4 (or IPv6) as the transport
37 layer, but implements a real network protocol; and there's the presentation
38 layer which renders structured data to binary blobs and back again using XDR
54 (1) Part of an RxRPC facility for both kernel and userspace applications by
55 making the session part of it a Linux network protocol (AF_RXRPC).
57 (2) A two-phase protocol. The client transmits a blob (the request) and then
58 receives a blob (the reply), and the server receives the request and then
61 (3) Retention of the reusable bits of the transport system set up for one call
62 to speed up subsequent calls.
64 (4) A secure protocol, using the Linux kernel's key retention facility to
65 manage security on the client end. The server end must of necessity be
66 more active in security negotiations.
68 AF_RXRPC does not provide XDR marshalling/presentation facilities. That is
69 left to the application. AF_RXRPC only deals in blobs. Even the operation ID
70 is just the first four bytes of the request blob, and as such is beyond the
74 Sockets of AF_RXRPC family are:
76 (1) created as type SOCK_DGRAM;
78 (2) provided with a protocol of the type of underlying transport they're going
79 to use - currently only PF_INET is supported.
82 The Andrew File System (AFS) is an example of an application that uses this and
83 that has both kernel (filesystem) and userspace (utility) components.
86 ======================
87 RXRPC PROTOCOL SUMMARY
88 ======================
90 An overview of the RxRPC protocol:
92 (*) RxRPC sits on top of another networking protocol (UDP is the only option
93 currently), and uses this to provide network transport. UDP ports, for
94 example, provide transport endpoints.
96 (*) RxRPC supports multiple virtual "connections" from any given transport
97 endpoint, thus allowing the endpoints to be shared, even to the same
100 (*) Each connection goes to a particular "service". A connection may not go
101 to multiple services. A service may be considered the RxRPC equivalent of
102 a port number. AF_RXRPC permits multiple services to share an endpoint.
104 (*) Client-originating packets are marked, thus a transport endpoint can be
105 shared between client and server connections (connections have a
108 (*) Up to a billion connections may be supported concurrently between one
109 local transport endpoint and one service on one remote endpoint. An RxRPC
110 connection is described by seven numbers:
113 Local port } Transport (UDP) address
120 (*) Each RxRPC operation is a "call". A connection may make up to four
121 billion calls, but only up to four calls may be in progress on a
122 connection at any one time.
124 (*) Calls are two-phase and asymmetric: the client sends its request data,
125 which the service receives; then the service transmits the reply data
126 which the client receives.
128 (*) The data blobs are of indefinite size, the end of a phase is marked with a
129 flag in the packet. The number of packets of data making up one blob may
130 not exceed 4 billion, however, as this would cause the sequence number to
133 (*) The first four bytes of the request data are the service operation ID.
135 (*) Security is negotiated on a per-connection basis. The connection is
136 initiated by the first data packet on it arriving. If security is
137 requested, the server then issues a "challenge" and then the client
138 replies with a "response". If the response is successful, the security is
139 set for the lifetime of that connection, and all subsequent calls made
140 upon it use that same security. In the event that the server lets a
141 connection lapse before the client, the security will be renegotiated if
142 the client uses the connection again.
144 (*) Calls use ACK packets to handle reliability. Data packets are also
145 explicitly sequenced per call.
147 (*) There are two types of positive acknowledgement: hard-ACKs and soft-ACKs.
148 A hard-ACK indicates to the far side that all the data received to a point
149 has been received and processed; a soft-ACK indicates that the data has
150 been received but may yet be discarded and re-requested. The sender may
151 not discard any transmittable packets until they've been hard-ACK'd.
153 (*) Reception of a reply data packet implicitly hard-ACK's all the data
154 packets that make up the request.
156 (*) An call is complete when the request has been sent, the reply has been
157 received and the final hard-ACK on the last packet of the reply has
160 (*) An call may be aborted by either end at any time up to its completion.
163 =====================
164 AF_RXRPC DRIVER MODEL
165 =====================
167 About the AF_RXRPC driver:
169 (*) The AF_RXRPC protocol transparently uses internal sockets of the transport
170 protocol to represent transport endpoints.
172 (*) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC
173 connections are handled transparently. One client socket may be used to
174 make multiple simultaneous calls to the same service. One server socket
175 may handle calls from many clients.
177 (*) Additional parallel client connections will be initiated to support extra
178 concurrent calls, up to a tunable limit.
180 (*) Each connection is retained for a certain amount of time [tunable] after
181 the last call currently using it has completed in case a new call is made
184 (*) Each internal UDP socket is retained [tunable] for a certain amount of
185 time [tunable] after the last connection using it discarded, in case a new
186 connection is made that could use it.
188 (*) A client-side connection is only shared between calls if they have have
189 the same key struct describing their security (and assuming the calls
190 would otherwise share the connection). Non-secured calls would also be
191 able to share connections with each other.
193 (*) A server-side connection is shared if the client says it is.
195 (*) ACK'ing is handled by the protocol driver automatically, including ping
198 (*) SO_KEEPALIVE automatically pings the other side to keep the connection
201 (*) If an ICMP error is received, all calls affected by that error will be
202 aborted with an appropriate network error passed through recvmsg().
205 Interaction with the user of the RxRPC socket:
207 (*) A socket is made into a server socket by binding an address with a
210 (*) In the client, sending a request is achieved with one or more sendmsgs,
211 followed by the reply being received with one or more recvmsgs.
213 (*) The first sendmsg for a request to be sent from a client contains a tag to
214 be used in all other sendmsgs or recvmsgs associated with that call. The
215 tag is carried in the control data.
217 (*) connect() is used to supply a default destination address for a client
218 socket. This may be overridden by supplying an alternate address to the
219 first sendmsg() of a call (struct msghdr::msg_name).
221 (*) If connect() is called on an unbound client, a random local port will
222 bound before the operation takes place.
224 (*) A server socket may also be used to make client calls. To do this, the
225 first sendmsg() of the call must specify the target address. The server's
226 transport endpoint is used to send the packets.
228 (*) Once the application has received the last message associated with a call,
229 the tag is guaranteed not to be seen again, and so it can be used to pin
230 client resources. A new call can then be initiated with the same tag
231 without fear of interference.
233 (*) In the server, a request is received with one or more recvmsgs, then the
234 the reply is transmitted with one or more sendmsgs, and then the final ACK
235 is received with a last recvmsg.
237 (*) When sending data for a call, sendmsg is given MSG_MORE if there's more
238 data to come on that call.
240 (*) When receiving data for a call, recvmsg flags MSG_MORE if there's more
241 data to come for that call.
243 (*) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg
244 to indicate the terminal message for that call.
246 (*) A call may be aborted by adding an abort control message to the control
247 data. Issuing an abort terminates the kernel's use of that call's tag.
248 Any messages waiting in the receive queue for that call will be discarded.
250 (*) Aborts, busy notifications and challenge packets are delivered by recvmsg,
251 and control data messages will be set to indicate the context. Receiving
252 an abort or a busy message terminates the kernel's use of that call's tag.
254 (*) The control data part of the msghdr struct is used for a number of things:
256 (*) The tag of the intended or affected call.
258 (*) Sending or receiving errors, aborts and busy notifications.
260 (*) Notifications of incoming calls.
262 (*) Sending debug requests and receiving debug replies [TODO].
264 (*) When the kernel has received and set up an incoming call, it sends a
265 message to server application to let it know there's a new call awaiting
266 its acceptance [recvmsg reports a special control message]. The server
267 application then uses sendmsg to assign a tag to the new call. Once that
268 is done, the first part of the request data will be delivered by recvmsg.
270 (*) The server application has to provide the server socket with a keyring of
271 secret keys corresponding to the security types it permits. When a secure
272 connection is being set up, the kernel looks up the appropriate secret key
273 in the keyring and then sends a challenge packet to the client and
274 receives a response packet. The kernel then checks the authorisation of
275 the packet and either aborts the connection or sets up the security.
277 (*) The name of the key a client will use to secure its communications is
278 nominated by a socket option.
283 (*) If there's a sequence of data messages belonging to a particular call on
284 the receive queue, then recvmsg will keep working through them until:
286 (a) it meets the end of that call's received data,
288 (b) it meets a non-data message,
290 (c) it meets a message belonging to a different call, or
292 (d) it fills the user buffer.
294 If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
295 reception of further data, until one of the above four conditions is met.
297 (2) MSG_PEEK operates similarly, but will return immediately if it has put any
298 data in the buffer rather than sleeping until it can fill the buffer.
300 (3) If a data message is only partially consumed in filling a user buffer,
301 then the remainder of that message will be left on the front of the queue
302 for the next taker. MSG_TRUNC will never be flagged.
304 (4) If there is more data to be had on a call (it hasn't copied the last byte
305 of the last data message in that phase yet), then MSG_MORE will be
313 AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
314 calls, to invoke certain actions and to report certain conditions. These are:
316 MESSAGE ID SRT DATA MEANING
317 ======================= === =========== ===============================
318 RXRPC_USER_CALL_ID sr- User ID App's call specifier
319 RXRPC_ABORT srt Abort code Abort code to issue/received
320 RXRPC_ACK -rt n/a Final ACK received
321 RXRPC_NET_ERROR -rt error num Network error on call
322 RXRPC_BUSY -rt n/a Call rejected (server busy)
323 RXRPC_LOCAL_ERROR -rt error num Local error encountered
324 RXRPC_NEW_CALL -r- n/a New call received
325 RXRPC_ACCEPT s-- n/a Accept new call
327 (SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
329 (*) RXRPC_USER_CALL_ID
331 This is used to indicate the application's call ID. It's an unsigned long
332 that the app specifies in the client by attaching it to the first data
333 message or in the server by passing it in association with an RXRPC_ACCEPT
334 message. recvmsg() passes it in conjunction with all messages except
335 those of the RXRPC_NEW_CALL message.
339 This is can be used by an application to abort a call by passing it to
340 sendmsg, or it can be delivered by recvmsg to indicate a remote abort was
341 received. Either way, it must be associated with an RXRPC_USER_CALL_ID to
342 specify the call affected. If an abort is being sent, then error EBADSLT
343 will be returned if there is no call with that user ID.
347 This is delivered to a server application to indicate that the final ACK
348 of a call was received from the client. It will be associated with an
349 RXRPC_USER_CALL_ID to indicate the call that's now complete.
353 This is delivered to an application to indicate that an ICMP error message
354 was encountered in the process of trying to talk to the peer. An
355 errno-class integer value will be included in the control message data
356 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
361 This is delivered to a client application to indicate that a call was
362 rejected by the server due to the server being busy. It will be
363 associated with an RXRPC_USER_CALL_ID to indicate the rejected call.
365 (*) RXRPC_LOCAL_ERROR
367 This is delivered to an application to indicate that a local error was
368 encountered and that a call has been aborted because of it. An
369 errno-class integer value will be included in the control message data
370 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
375 This is delivered to indicate to a server application that a new call has
376 arrived and is awaiting acceptance. No user ID is associated with this,
377 as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT.
381 This is used by a server application to attempt to accept a call and
382 assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID
383 to indicate the user ID to be assigned. If there is no call to be
384 accepted (it may have timed out, been aborted, etc.), then sendmsg will
385 return error ENODATA. If the user ID is already in use by another call,
386 then error EBADSLT will be returned.
393 AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:
395 (*) RXRPC_SECURITY_KEY
397 This is used to specify the description of the key to be used. The key is
398 extracted from the calling process's keyrings with request_key() and
399 should be of "rxrpc" type.
401 The optval pointer points to the description string, and optlen indicates
402 how long the string is, without the NUL terminator.
404 (*) RXRPC_SECURITY_KEYRING
406 Similar to above but specifies a keyring of server secret keys to use (key
407 type "keyring"). See the "Security" section.
409 (*) RXRPC_EXCLUSIVE_CONNECTION
411 This is used to request that new connections should be used for each call
412 made subsequently on this socket. optval should be NULL and optlen 0.
414 (*) RXRPC_MIN_SECURITY_LEVEL
416 This is used to specify the minimum security level required for calls on
417 this socket. optval must point to an int containing one of the following
420 (a) RXRPC_SECURITY_PLAIN
422 Encrypted checksum only.
424 (b) RXRPC_SECURITY_AUTH
426 Encrypted checksum plus packet padded and first eight bytes of packet
427 encrypted - which includes the actual packet length.
429 (c) RXRPC_SECURITY_ENCRYPTED
431 Encrypted checksum plus entire packet padded and encrypted, including
432 actual packet length.
439 Currently, only the kerberos 4 equivalent protocol has been implemented
440 (security index 2 - rxkad). This requires the rxkad module to be loaded and,
441 on the client, tickets of the appropriate type to be obtained from the AFS
442 kaserver or the kerberos server and installed as "rxrpc" type keys. This is
443 normally done using the klog program. An example simple klog program can be
446 http://people.redhat.com/~dhowells/rxrpc/klog.c
448 The payload provided to add_key() on the client should be of the following
451 struct rxrpc_key_sec2_v1 {
452 uint16_t security_index; /* 2 */
453 uint16_t ticket_length; /* length of ticket[] */
454 uint32_t expiry; /* time at which expires */
455 uint8_t kvno; /* key version number */
457 uint8_t session_key[8]; /* DES session key */
458 uint8_t ticket[0]; /* the encrypted ticket */
461 Where the ticket blob is just appended to the above structure.
464 For the server, keys of type "rxrpc_s" must be made available to the server.
465 They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an
466 rxkad key for the AFS VL service). When such a key is created, it should be
467 given the server's secret key as the instantiation data (see the example
470 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
472 A keyring is passed to the server socket by naming it in a sockopt. The server
473 socket then looks the server secret keys up in this keyring when secure
474 incoming connections are made. This can be seen in an example program that can
477 http://people.redhat.com/~dhowells/rxrpc/listen.c
484 A client would issue an operation by:
486 (1) An RxRPC socket is set up by:
488 client = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
490 Where the third parameter indicates the protocol family of the transport
491 socket used - usually IPv4 but it can also be IPv6 [TODO].
493 (2) A local address can optionally be bound:
495 struct sockaddr_rxrpc srx = {
496 .srx_family = AF_RXRPC,
497 .srx_service = 0, /* we're a client */
498 .transport_type = SOCK_DGRAM, /* type of transport socket */
499 .transport.sin_family = AF_INET,
500 .transport.sin_port = htons(7000), /* AFS callback */
501 .transport.sin_address = 0, /* all local interfaces */
503 bind(client, &srx, sizeof(srx));
505 This specifies the local UDP port to be used. If not given, a random
506 non-privileged port will be used. A UDP port may be shared between
507 several unrelated RxRPC sockets. Security is handled on a basis of
508 per-RxRPC virtual connection.
510 (3) The security is set:
512 const char *key = "AFS:cambridge.redhat.com";
513 setsockopt(client, SOL_RXRPC, RXRPC_SECURITY_KEY, key, strlen(key));
515 This issues a request_key() to get the key representing the security
516 context. The minimum security level can be set:
518 unsigned int sec = RXRPC_SECURITY_ENCRYPTED;
519 setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
522 (4) The server to be contacted can then be specified (alternatively this can
523 be done through sendmsg):
525 struct sockaddr_rxrpc srx = {
526 .srx_family = AF_RXRPC,
527 .srx_service = VL_SERVICE_ID,
528 .transport_type = SOCK_DGRAM, /* type of transport socket */
529 .transport.sin_family = AF_INET,
530 .transport.sin_port = htons(7005), /* AFS volume manager */
531 .transport.sin_address = ...,
533 connect(client, &srx, sizeof(srx));
535 (5) The request data should then be posted to the server socket using a series
536 of sendmsg() calls, each with the following control message attached:
538 RXRPC_USER_CALL_ID - specifies the user ID for this call
540 MSG_MORE should be set in msghdr::msg_flags on all but the last part of
541 the request. Multiple requests may be made simultaneously.
543 If a call is intended to go to a destination other than the default
544 specified through connect(), then msghdr::msg_name should be set on the
545 first request message of that call.
547 (6) The reply data will then be posted to the server socket for recvmsg() to
548 pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data
549 for a particular call to be read. MSG_EOR will be set on the terminal
552 All data will be delivered with the following control message attached:
554 RXRPC_USER_CALL_ID - specifies the user ID for this call
556 If an abort or error occurred, this will be returned in the control data
557 buffer instead, and MSG_EOR will be flagged to indicate the end of that
565 A server would be set up to accept operations in the following manner:
567 (1) An RxRPC socket is created by:
569 server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
571 Where the third parameter indicates the address type of the transport
572 socket used - usually IPv4.
574 (2) Security is set up if desired by giving the socket a keyring with server
577 keyring = add_key("keyring", "AFSkeys", NULL, 0,
578 KEY_SPEC_PROCESS_KEYRING);
580 const char secret_key[8] = {
581 0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 };
582 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
584 setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7);
586 The keyring can be manipulated after it has been given to the socket. This
587 permits the server to add more keys, replace keys, etc. whilst it is live.
589 (2) A local address must then be bound:
591 struct sockaddr_rxrpc srx = {
592 .srx_family = AF_RXRPC,
593 .srx_service = VL_SERVICE_ID, /* RxRPC service ID */
594 .transport_type = SOCK_DGRAM, /* type of transport socket */
595 .transport.sin_family = AF_INET,
596 .transport.sin_port = htons(7000), /* AFS callback */
597 .transport.sin_address = 0, /* all local interfaces */
599 bind(server, &srx, sizeof(srx));
601 (3) The server is then set to listen out for incoming calls:
605 (4) The kernel notifies the server of pending incoming connections by sending
606 it a message for each. This is received with recvmsg() on the server
607 socket. It has no data, and has a single dataless control message
612 The address that can be passed back by recvmsg() at this point should be
613 ignored since the call for which the message was posted may have gone by
614 the time it is accepted - in which case the first call still on the queue
617 (5) The server then accepts the new call by issuing a sendmsg() with two
618 pieces of control data and no actual data:
620 RXRPC_ACCEPT - indicate connection acceptance
621 RXRPC_USER_CALL_ID - specify user ID for this call
623 (6) The first request data packet will then be posted to the server socket for
624 recvmsg() to pick up. At that point, the RxRPC address for the call can
625 be read from the address fields in the msghdr struct.
627 Subsequent request data will be posted to the server socket for recvmsg()
628 to collect as it arrives. All but the last piece of the request data will
629 be delivered with MSG_MORE flagged.
631 All data will be delivered with the following control message attached:
633 RXRPC_USER_CALL_ID - specifies the user ID for this call
635 (8) The reply data should then be posted to the server socket using a series
636 of sendmsg() calls, each with the following control messages attached:
638 RXRPC_USER_CALL_ID - specifies the user ID for this call
640 MSG_MORE should be set in msghdr::msg_flags on all but the last message
641 for a particular call.
643 (9) The final ACK from the client will be posted for retrieval by recvmsg()
644 when it is received. It will take the form of a dataless message with two
645 control messages attached:
647 RXRPC_USER_CALL_ID - specifies the user ID for this call
648 RXRPC_ACK - indicates final ACK (no data)
650 MSG_EOR will be flagged to indicate that this is the final message for
653 (10) Up to the point the final packet of reply data is sent, the call can be
654 aborted by calling sendmsg() with a dataless message with the following
655 control messages attached:
657 RXRPC_USER_CALL_ID - specifies the user ID for this call
658 RXRPC_ABORT - indicates abort code (4 byte data)
660 Any packets waiting in the socket's receive queue will be discarded if
663 Note that all the communications for a particular service take place through
664 the one server socket, using control messages on sendmsg() and recvmsg() to
665 determine the call affected.
668 =========================
669 AF_RXRPC KERNEL INTERFACE
670 =========================
672 The AF_RXRPC module also provides an interface for use by in-kernel utilities
673 such as the AFS filesystem. This permits such a utility to:
675 (1) Use different keys directly on individual client calls on one socket
676 rather than having to open a whole slew of sockets, one for each key it
679 (2) Avoid having RxRPC call request_key() at the point of issue of a call or
680 opening of a socket. Instead the utility is responsible for requesting a
681 key at the appropriate point. AFS, for instance, would do this during VFS
682 operations such as open() or unlink(). The key is then handed through
683 when the call is initiated.
685 (3) Request the use of something other than GFP_KERNEL to allocate memory.
687 (4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be
688 intercepted before they get put into the socket Rx queue and the socket
689 buffers manipulated directly.
691 To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,
692 bind an address as appropriate and listen if it's to be a server socket, but
693 then it passes this to the kernel interface functions.
695 The kernel interface functions are as follows:
697 (*) Begin a new client call.
700 rxrpc_kernel_begin_call(struct socket *sock,
701 struct sockaddr_rxrpc *srx,
703 unsigned long user_call_ID,
706 This allocates the infrastructure to make a new RxRPC call and assigns
707 call and connection numbers. The call will be made on the UDP port that
708 the socket is bound to. The call will go to the destination address of a
709 connected client socket unless an alternative is supplied (srx is
712 If a key is supplied then this will be used to secure the call instead of
713 the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls
714 secured in this way will still share connections if at all possible.
716 The user_call_ID is equivalent to that supplied to sendmsg() in the
717 control data buffer. It is entirely feasible to use this to point to a
718 kernel data structure.
720 If this function is successful, an opaque reference to the RxRPC call is
721 returned. The caller now holds a reference on this and it must be
724 (*) End a client call.
726 void rxrpc_kernel_end_call(struct rxrpc_call *call);
728 This is used to end a previously begun call. The user_call_ID is expunged
729 from AF_RXRPC's knowledge and will not be seen again in association with
732 (*) Send data through a call.
734 int rxrpc_kernel_send_data(struct rxrpc_call *call, struct msghdr *msg,
737 This is used to supply either the request part of a client call or the
738 reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the
739 data buffers to be used. msg_iov may not be NULL and must point
740 exclusively to in-kernel virtual addresses. msg.msg_flags may be given
741 MSG_MORE if there will be subsequent data sends for this call.
743 The msg must not specify a destination address, control data or any flags
744 other than MSG_MORE. len is the total amount of data to transmit.
748 void rxrpc_kernel_abort_call(struct rxrpc_call *call, u32 abort_code);
750 This is used to abort a call if it's still in an abortable state. The
751 abort code specified will be placed in the ABORT message sent.
753 (*) Intercept received RxRPC messages.
755 typedef void (*rxrpc_interceptor_t)(struct sock *sk,
756 unsigned long user_call_ID,
757 struct sk_buff *skb);
760 rxrpc_kernel_intercept_rx_messages(struct socket *sock,
761 rxrpc_interceptor_t interceptor);
763 This installs an interceptor function on the specified AF_RXRPC socket.
764 All messages that would otherwise wind up in the socket's Rx queue are
765 then diverted to this function. Note that care must be taken to process
766 the messages in the right order to maintain DATA message sequentiality.
768 The interceptor function itself is provided with the address of the socket
769 and handling the incoming message, the ID assigned by the kernel utility
770 to the call and the socket buffer containing the message.
772 The skb->mark field indicates the type of message:
775 =============================== =======================================
776 RXRPC_SKB_MARK_DATA Data message
777 RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call
778 RXRPC_SKB_MARK_BUSY Client call rejected as server busy
779 RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer
780 RXRPC_SKB_MARK_NET_ERROR Network error detected
781 RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered
782 RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance
784 The remote abort message can be probed with rxrpc_kernel_get_abort_code().
785 The two error messages can be probed with rxrpc_kernel_get_error_number().
786 A new call can be accepted with rxrpc_kernel_accept_call().
788 Data messages can have their contents extracted with the usual bunch of
789 socket buffer manipulation functions. A data message can be determined to
790 be the last one in a sequence with rxrpc_kernel_is_data_last(). When a
791 data message has been used up, rxrpc_kernel_data_delivered() should be
794 Non-data messages should be handled to rxrpc_kernel_free_skb() to dispose
795 of. It is possible to get extra refs on all types of message for later
796 freeing, but this may pin the state of a call until the message is finally
799 (*) Accept an incoming call.
802 rxrpc_kernel_accept_call(struct socket *sock,
803 unsigned long user_call_ID);
805 This is used to accept an incoming call and to assign it a call ID. This
806 function is similar to rxrpc_kernel_begin_call() and calls accepted must
807 be ended in the same way.
809 If this function is successful, an opaque reference to the RxRPC call is
810 returned. The caller now holds a reference on this and it must be
813 (*) Reject an incoming call.
815 int rxrpc_kernel_reject_call(struct socket *sock);
817 This is used to reject the first incoming call on the socket's queue with
818 a BUSY message. -ENODATA is returned if there were no incoming calls.
819 Other errors may be returned if the call had been aborted (-ECONNABORTED)
820 or had timed out (-ETIME).
822 (*) Record the delivery of a data message and free it.
824 void rxrpc_kernel_data_delivered(struct sk_buff *skb);
826 This is used to record a data message as having been delivered and to
827 update the ACK state for the call. The socket buffer will be freed.
831 void rxrpc_kernel_free_skb(struct sk_buff *skb);
833 This is used to free a non-DATA socket buffer intercepted from an AF_RXRPC
836 (*) Determine if a data message is the last one on a call.
838 bool rxrpc_kernel_is_data_last(struct sk_buff *skb);
840 This is used to determine if a socket buffer holds the last data message
841 to be received for a call (true will be returned if it does, false
844 The data message will be part of the reply on a client call and the
845 request on an incoming call. In the latter case there will be more
846 messages, but in the former case there will not.
848 (*) Get the abort code from an abort message.
850 u32 rxrpc_kernel_get_abort_code(struct sk_buff *skb);
852 This is used to extract the abort code from a remote abort message.
854 (*) Get the error number from a local or network error message.
856 int rxrpc_kernel_get_error_number(struct sk_buff *skb);
858 This is used to extract the error number from a message indicating either
859 a local error occurred or a network error occurred.
861 (*) Allocate a null key for doing anonymous security.
863 struct key *rxrpc_get_null_key(const char *keyname);
865 This is used to allocate a null RxRPC key that can be used to indicate
866 anonymous security for a particular domain.