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1 ======================
2 RxRPC NETWORK PROTOCOL
3 ======================
4
5The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
6that can be used to perform RxRPC remote operations. This is done over sockets
7of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and
8receive data, aborts and errors.
9
10Contents of this document:
11
12 (*) Overview.
13
14 (*) RxRPC protocol summary.
15
16 (*) AF_RXRPC driver model.
17
18 (*) Control messages.
19
20 (*) Socket options.
21
22 (*) Security.
23
24 (*) Example client usage.
25
26 (*) Example server usage.
27
28 (*) AF_RXRPC kernel interface.
29
30 (*) Configurable parameters.
31
32
33========
34OVERVIEW
35========
36
37RxRPC is a two-layer protocol. There is a session layer which provides
38reliable virtual connections using UDP over IPv4 (or IPv6) as the transport
39layer, but implements a real network protocol; and there's the presentation
40layer which renders structured data to binary blobs and back again using XDR
41(as does SunRPC):
42
43 +-------------+
44 | Application |
45 +-------------+
46 | XDR | Presentation
47 +-------------+
48 | RxRPC | Session
49 +-------------+
50 | UDP | Transport
51 +-------------+
52
53
54AF_RXRPC provides:
55
56 (1) Part of an RxRPC facility for both kernel and userspace applications by
57 making the session part of it a Linux network protocol (AF_RXRPC).
58
59 (2) A two-phase protocol. The client transmits a blob (the request) and then
60 receives a blob (the reply), and the server receives the request and then
61 transmits the reply.
62
63 (3) Retention of the reusable bits of the transport system set up for one call
64 to speed up subsequent calls.
65
66 (4) A secure protocol, using the Linux kernel's key retention facility to
67 manage security on the client end. The server end must of necessity be
68 more active in security negotiations.
69
70AF_RXRPC does not provide XDR marshalling/presentation facilities. That is
71left to the application. AF_RXRPC only deals in blobs. Even the operation ID
72is just the first four bytes of the request blob, and as such is beyond the
73kernel's interest.
74
75
76Sockets of AF_RXRPC family are:
77
78 (1) created as type SOCK_DGRAM;
79
80 (2) provided with a protocol of the type of underlying transport they're going
81 to use - currently only PF_INET is supported.
82
83
84The Andrew File System (AFS) is an example of an application that uses this and
85that has both kernel (filesystem) and userspace (utility) components.
86
87
88======================
89RXRPC PROTOCOL SUMMARY
90======================
91
92An overview of the RxRPC protocol:
93
94 (*) RxRPC sits on top of another networking protocol (UDP is the only option
95 currently), and uses this to provide network transport. UDP ports, for
96 example, provide transport endpoints.
97
98 (*) RxRPC supports multiple virtual "connections" from any given transport
99 endpoint, thus allowing the endpoints to be shared, even to the same
100 remote endpoint.
101
102 (*) Each connection goes to a particular "service". A connection may not go
103 to multiple services. A service may be considered the RxRPC equivalent of
104 a port number. AF_RXRPC permits multiple services to share an endpoint.
105
106 (*) Client-originating packets are marked, thus a transport endpoint can be
107 shared between client and server connections (connections have a
108 direction).
109
110 (*) Up to a billion connections may be supported concurrently between one
111 local transport endpoint and one service on one remote endpoint. An RxRPC
112 connection is described by seven numbers:
113
114 Local address }
115 Local port } Transport (UDP) address
116 Remote address }
117 Remote port }
118 Direction
119 Connection ID
120 Service ID
121
122 (*) Each RxRPC operation is a "call". A connection may make up to four
123 billion calls, but only up to four calls may be in progress on a
124 connection at any one time.
125
126 (*) Calls are two-phase and asymmetric: the client sends its request data,
127 which the service receives; then the service transmits the reply data
128 which the client receives.
129
130 (*) The data blobs are of indefinite size, the end of a phase is marked with a
131 flag in the packet. The number of packets of data making up one blob may
132 not exceed 4 billion, however, as this would cause the sequence number to
133 wrap.
134
135 (*) The first four bytes of the request data are the service operation ID.
136
137 (*) Security is negotiated on a per-connection basis. The connection is
138 initiated by the first data packet on it arriving. If security is
139 requested, the server then issues a "challenge" and then the client
140 replies with a "response". If the response is successful, the security is
141 set for the lifetime of that connection, and all subsequent calls made
142 upon it use that same security. In the event that the server lets a
143 connection lapse before the client, the security will be renegotiated if
144 the client uses the connection again.
145
146 (*) Calls use ACK packets to handle reliability. Data packets are also
147 explicitly sequenced per call.
148
149 (*) There are two types of positive acknowledgment: hard-ACKs and soft-ACKs.
150 A hard-ACK indicates to the far side that all the data received to a point
151 has been received and processed; a soft-ACK indicates that the data has
152 been received but may yet be discarded and re-requested. The sender may
153 not discard any transmittable packets until they've been hard-ACK'd.
154
155 (*) Reception of a reply data packet implicitly hard-ACK's all the data
156 packets that make up the request.
157
158 (*) An call is complete when the request has been sent, the reply has been
159 received and the final hard-ACK on the last packet of the reply has
160 reached the server.
161
162 (*) An call may be aborted by either end at any time up to its completion.
163
164
165=====================
166AF_RXRPC DRIVER MODEL
167=====================
168
169About the AF_RXRPC driver:
170
171 (*) The AF_RXRPC protocol transparently uses internal sockets of the transport
172 protocol to represent transport endpoints.
173
174 (*) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC
175 connections are handled transparently. One client socket may be used to
176 make multiple simultaneous calls to the same service. One server socket
177 may handle calls from many clients.
178
179 (*) Additional parallel client connections will be initiated to support extra
180 concurrent calls, up to a tunable limit.
181
182 (*) Each connection is retained for a certain amount of time [tunable] after
183 the last call currently using it has completed in case a new call is made
184 that could reuse it.
185
186 (*) Each internal UDP socket is retained [tunable] for a certain amount of
187 time [tunable] after the last connection using it discarded, in case a new
188 connection is made that could use it.
189
190 (*) A client-side connection is only shared between calls if they have have
191 the same key struct describing their security (and assuming the calls
192 would otherwise share the connection). Non-secured calls would also be
193 able to share connections with each other.
194
195 (*) A server-side connection is shared if the client says it is.
196
197 (*) ACK'ing is handled by the protocol driver automatically, including ping
198 replying.
199
200 (*) SO_KEEPALIVE automatically pings the other side to keep the connection
201 alive [TODO].
202
203 (*) If an ICMP error is received, all calls affected by that error will be
204 aborted with an appropriate network error passed through recvmsg().
205
206
207Interaction with the user of the RxRPC socket:
208
209 (*) A socket is made into a server socket by binding an address with a
210 non-zero service ID.
211
212 (*) In the client, sending a request is achieved with one or more sendmsgs,
213 followed by the reply being received with one or more recvmsgs.
214
215 (*) The first sendmsg for a request to be sent from a client contains a tag to
216 be used in all other sendmsgs or recvmsgs associated with that call. The
217 tag is carried in the control data.
218
219 (*) connect() is used to supply a default destination address for a client
220 socket. This may be overridden by supplying an alternate address to the
221 first sendmsg() of a call (struct msghdr::msg_name).
222
223 (*) If connect() is called on an unbound client, a random local port will
224 bound before the operation takes place.
225
226 (*) A server socket may also be used to make client calls. To do this, the
227 first sendmsg() of the call must specify the target address. The server's
228 transport endpoint is used to send the packets.
229
230 (*) Once the application has received the last message associated with a call,
231 the tag is guaranteed not to be seen again, and so it can be used to pin
232 client resources. A new call can then be initiated with the same tag
233 without fear of interference.
234
235 (*) In the server, a request is received with one or more recvmsgs, then the
236 the reply is transmitted with one or more sendmsgs, and then the final ACK
237 is received with a last recvmsg.
238
239 (*) When sending data for a call, sendmsg is given MSG_MORE if there's more
240 data to come on that call.
241
242 (*) When receiving data for a call, recvmsg flags MSG_MORE if there's more
243 data to come for that call.
244
245 (*) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg
246 to indicate the terminal message for that call.
247
248 (*) A call may be aborted by adding an abort control message to the control
249 data. Issuing an abort terminates the kernel's use of that call's tag.
250 Any messages waiting in the receive queue for that call will be discarded.
251
252 (*) Aborts, busy notifications and challenge packets are delivered by recvmsg,
253 and control data messages will be set to indicate the context. Receiving
254 an abort or a busy message terminates the kernel's use of that call's tag.
255
256 (*) The control data part of the msghdr struct is used for a number of things:
257
258 (*) The tag of the intended or affected call.
259
260 (*) Sending or receiving errors, aborts and busy notifications.
261
262 (*) Notifications of incoming calls.
263
264 (*) Sending debug requests and receiving debug replies [TODO].
265
266 (*) When the kernel has received and set up an incoming call, it sends a
267 message to server application to let it know there's a new call awaiting
268 its acceptance [recvmsg reports a special control message]. The server
269 application then uses sendmsg to assign a tag to the new call. Once that
270 is done, the first part of the request data will be delivered by recvmsg.
271
272 (*) The server application has to provide the server socket with a keyring of
273 secret keys corresponding to the security types it permits. When a secure
274 connection is being set up, the kernel looks up the appropriate secret key
275 in the keyring and then sends a challenge packet to the client and
276 receives a response packet. The kernel then checks the authorisation of
277 the packet and either aborts the connection or sets up the security.
278
279 (*) The name of the key a client will use to secure its communications is
280 nominated by a socket option.
281
282
283Notes on sendmsg:
284
285 (*) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is
286 making progress at accepting packets within a reasonable time such that we
287 manage to queue up all the data for transmission. This requires the
288 client to accept at least one packet per 2*RTT time period.
289
290 If this isn't set, sendmsg() will return immediately, either returning
291 EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data
292 consumed.
293
294
295Notes on recvmsg:
296
297 (*) If there's a sequence of data messages belonging to a particular call on
298 the receive queue, then recvmsg will keep working through them until:
299
300 (a) it meets the end of that call's received data,
301
302 (b) it meets a non-data message,
303
304 (c) it meets a message belonging to a different call, or
305
306 (d) it fills the user buffer.
307
308 If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
309 reception of further data, until one of the above four conditions is met.
310
311 (2) MSG_PEEK operates similarly, but will return immediately if it has put any
312 data in the buffer rather than sleeping until it can fill the buffer.
313
314 (3) If a data message is only partially consumed in filling a user buffer,
315 then the remainder of that message will be left on the front of the queue
316 for the next taker. MSG_TRUNC will never be flagged.
317
318 (4) If there is more data to be had on a call (it hasn't copied the last byte
319 of the last data message in that phase yet), then MSG_MORE will be
320 flagged.
321
322
323================
324CONTROL MESSAGES
325================
326
327AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
328calls, to invoke certain actions and to report certain conditions. These are:
329
330 MESSAGE ID SRT DATA MEANING
331 ======================= === =========== ===============================
332 RXRPC_USER_CALL_ID sr- User ID App's call specifier
333 RXRPC_ABORT srt Abort code Abort code to issue/received
334 RXRPC_ACK -rt n/a Final ACK received
335 RXRPC_NET_ERROR -rt error num Network error on call
336 RXRPC_BUSY -rt n/a Call rejected (server busy)
337 RXRPC_LOCAL_ERROR -rt error num Local error encountered
338 RXRPC_NEW_CALL -r- n/a New call received
339 RXRPC_ACCEPT s-- n/a Accept new call
340 RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call
341 RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded
342 RXRPC_TX_LENGTH s-- data len Total length of Tx data
343
344 (SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
345
346 (*) RXRPC_USER_CALL_ID
347
348 This is used to indicate the application's call ID. It's an unsigned long
349 that the app specifies in the client by attaching it to the first data
350 message or in the server by passing it in association with an RXRPC_ACCEPT
351 message. recvmsg() passes it in conjunction with all messages except
352 those of the RXRPC_NEW_CALL message.
353
354 (*) RXRPC_ABORT
355
356 This is can be used by an application to abort a call by passing it to
357 sendmsg, or it can be delivered by recvmsg to indicate a remote abort was
358 received. Either way, it must be associated with an RXRPC_USER_CALL_ID to
359 specify the call affected. If an abort is being sent, then error EBADSLT
360 will be returned if there is no call with that user ID.
361
362 (*) RXRPC_ACK
363
364 This is delivered to a server application to indicate that the final ACK
365 of a call was received from the client. It will be associated with an
366 RXRPC_USER_CALL_ID to indicate the call that's now complete.
367
368 (*) RXRPC_NET_ERROR
369
370 This is delivered to an application to indicate that an ICMP error message
371 was encountered in the process of trying to talk to the peer. An
372 errno-class integer value will be included in the control message data
373 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
374 affected.
375
376 (*) RXRPC_BUSY
377
378 This is delivered to a client application to indicate that a call was
379 rejected by the server due to the server being busy. It will be
380 associated with an RXRPC_USER_CALL_ID to indicate the rejected call.
381
382 (*) RXRPC_LOCAL_ERROR
383
384 This is delivered to an application to indicate that a local error was
385 encountered and that a call has been aborted because of it. An
386 errno-class integer value will be included in the control message data
387 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
388 affected.
389
390 (*) RXRPC_NEW_CALL
391
392 This is delivered to indicate to a server application that a new call has
393 arrived and is awaiting acceptance. No user ID is associated with this,
394 as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT.
395
396 (*) RXRPC_ACCEPT
397
398 This is used by a server application to attempt to accept a call and
399 assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID
400 to indicate the user ID to be assigned. If there is no call to be
401 accepted (it may have timed out, been aborted, etc.), then sendmsg will
402 return error ENODATA. If the user ID is already in use by another call,
403 then error EBADSLT will be returned.
404
405 (*) RXRPC_EXCLUSIVE_CALL
406
407 This is used to indicate that a client call should be made on a one-off
408 connection. The connection is discarded once the call has terminated.
409
410 (*) RXRPC_UPGRADE_SERVICE
411
412 This is used to make a client call to probe if the specified service ID
413 may be upgraded by the server. The caller must check msg_name returned to
414 recvmsg() for the service ID actually in use. The operation probed must
415 be one that takes the same arguments in both services.
416
417 Once this has been used to establish the upgrade capability (or lack
418 thereof) of the server, the service ID returned should be used for all
419 future communication to that server and RXRPC_UPGRADE_SERVICE should no
420 longer be set.
421
422 (*) RXRPC_TX_LENGTH
423
424 This is used to inform the kernel of the total amount of data that is
425 going to be transmitted by a call (whether in a client request or a
426 service response). If given, it allows the kernel to encrypt from the
427 userspace buffer directly to the packet buffers, rather than copying into
428 the buffer and then encrypting in place. This may only be given with the
429 first sendmsg() providing data for a call. EMSGSIZE will be generated if
430 the amount of data actually given is different.
431
432 This takes a parameter of __s64 type that indicates how much will be
433 transmitted. This may not be less than zero.
434
435The symbol RXRPC__SUPPORTED is defined as one more than the highest control
436message type supported. At run time this can be queried by means of the
437RXRPC_SUPPORTED_CMSG socket option (see below).
438
439
440==============
441SOCKET OPTIONS
442==============
443
444AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:
445
446 (*) RXRPC_SECURITY_KEY
447
448 This is used to specify the description of the key to be used. The key is
449 extracted from the calling process's keyrings with request_key() and
450 should be of "rxrpc" type.
451
452 The optval pointer points to the description string, and optlen indicates
453 how long the string is, without the NUL terminator.
454
455 (*) RXRPC_SECURITY_KEYRING
456
457 Similar to above but specifies a keyring of server secret keys to use (key
458 type "keyring"). See the "Security" section.
459
460 (*) RXRPC_EXCLUSIVE_CONNECTION
461
462 This is used to request that new connections should be used for each call
463 made subsequently on this socket. optval should be NULL and optlen 0.
464
465 (*) RXRPC_MIN_SECURITY_LEVEL
466
467 This is used to specify the minimum security level required for calls on
468 this socket. optval must point to an int containing one of the following
469 values:
470
471 (a) RXRPC_SECURITY_PLAIN
472
473 Encrypted checksum only.
474
475 (b) RXRPC_SECURITY_AUTH
476
477 Encrypted checksum plus packet padded and first eight bytes of packet
478 encrypted - which includes the actual packet length.
479
480 (c) RXRPC_SECURITY_ENCRYPTED
481
482 Encrypted checksum plus entire packet padded and encrypted, including
483 actual packet length.
484
485 (*) RXRPC_UPGRADEABLE_SERVICE
486
487 This is used to indicate that a service socket with two bindings may
488 upgrade one bound service to the other if requested by the client. optval
489 must point to an array of two unsigned short ints. The first is the
490 service ID to upgrade from and the second the service ID to upgrade to.
491
492 (*) RXRPC_SUPPORTED_CMSG
493
494 This is a read-only option that writes an int into the buffer indicating
495 the highest control message type supported.
496
497
498========
499SECURITY
500========
501
502Currently, only the kerberos 4 equivalent protocol has been implemented
503(security index 2 - rxkad). This requires the rxkad module to be loaded and,
504on the client, tickets of the appropriate type to be obtained from the AFS
505kaserver or the kerberos server and installed as "rxrpc" type keys. This is
506normally done using the klog program. An example simple klog program can be
507found at:
508
509 http://people.redhat.com/~dhowells/rxrpc/klog.c
510
511The payload provided to add_key() on the client should be of the following
512form:
513
514 struct rxrpc_key_sec2_v1 {
515 uint16_t security_index; /* 2 */
516 uint16_t ticket_length; /* length of ticket[] */
517 uint32_t expiry; /* time at which expires */
518 uint8_t kvno; /* key version number */
519 uint8_t __pad[3];
520 uint8_t session_key[8]; /* DES session key */
521 uint8_t ticket[0]; /* the encrypted ticket */
522 };
523
524Where the ticket blob is just appended to the above structure.
525
526
527For the server, keys of type "rxrpc_s" must be made available to the server.
528They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an
529rxkad key for the AFS VL service). When such a key is created, it should be
530given the server's secret key as the instantiation data (see the example
531below).
532
533 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
534
535A keyring is passed to the server socket by naming it in a sockopt. The server
536socket then looks the server secret keys up in this keyring when secure
537incoming connections are made. This can be seen in an example program that can
538be found at:
539
540 http://people.redhat.com/~dhowells/rxrpc/listen.c
541
542
543====================
544EXAMPLE CLIENT USAGE
545====================
546
547A client would issue an operation by:
548
549 (1) An RxRPC socket is set up by:
550
551 client = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
552
553 Where the third parameter indicates the protocol family of the transport
554 socket used - usually IPv4 but it can also be IPv6 [TODO].
555
556 (2) A local address can optionally be bound:
557
558 struct sockaddr_rxrpc srx = {
559 .srx_family = AF_RXRPC,
560 .srx_service = 0, /* we're a client */
561 .transport_type = SOCK_DGRAM, /* type of transport socket */
562 .transport.sin_family = AF_INET,
563 .transport.sin_port = htons(7000), /* AFS callback */
564 .transport.sin_address = 0, /* all local interfaces */
565 };
566 bind(client, &srx, sizeof(srx));
567
568 This specifies the local UDP port to be used. If not given, a random
569 non-privileged port will be used. A UDP port may be shared between
570 several unrelated RxRPC sockets. Security is handled on a basis of
571 per-RxRPC virtual connection.
572
573 (3) The security is set:
574
575 const char *key = "AFS:cambridge.redhat.com";
576 setsockopt(client, SOL_RXRPC, RXRPC_SECURITY_KEY, key, strlen(key));
577
578 This issues a request_key() to get the key representing the security
579 context. The minimum security level can be set:
580
581 unsigned int sec = RXRPC_SECURITY_ENCRYPTED;
582 setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
583 &sec, sizeof(sec));
584
585 (4) The server to be contacted can then be specified (alternatively this can
586 be done through sendmsg):
587
588 struct sockaddr_rxrpc srx = {
589 .srx_family = AF_RXRPC,
590 .srx_service = VL_SERVICE_ID,
591 .transport_type = SOCK_DGRAM, /* type of transport socket */
592 .transport.sin_family = AF_INET,
593 .transport.sin_port = htons(7005), /* AFS volume manager */
594 .transport.sin_address = ...,
595 };
596 connect(client, &srx, sizeof(srx));
597
598 (5) The request data should then be posted to the server socket using a series
599 of sendmsg() calls, each with the following control message attached:
600
601 RXRPC_USER_CALL_ID - specifies the user ID for this call
602
603 MSG_MORE should be set in msghdr::msg_flags on all but the last part of
604 the request. Multiple requests may be made simultaneously.
605
606 An RXRPC_TX_LENGTH control message can also be specified on the first
607 sendmsg() call.
608
609 If a call is intended to go to a destination other than the default
610 specified through connect(), then msghdr::msg_name should be set on the
611 first request message of that call.
612
613 (6) The reply data will then be posted to the server socket for recvmsg() to
614 pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data
615 for a particular call to be read. MSG_EOR will be set on the terminal
616 read for a call.
617
618 All data will be delivered with the following control message attached:
619
620 RXRPC_USER_CALL_ID - specifies the user ID for this call
621
622 If an abort or error occurred, this will be returned in the control data
623 buffer instead, and MSG_EOR will be flagged to indicate the end of that
624 call.
625
626A client may ask for a service ID it knows and ask that this be upgraded to a
627better service if one is available by supplying RXRPC_UPGRADE_SERVICE on the
628first sendmsg() of a call. The client should then check srx_service in the
629msg_name filled in by recvmsg() when collecting the result. srx_service will
630hold the same value as given to sendmsg() if the upgrade request was ignored by
631the service - otherwise it will be altered to indicate the service ID the
632server upgraded to. Note that the upgraded service ID is chosen by the server.
633The caller has to wait until it sees the service ID in the reply before sending
634any more calls (further calls to the same destination will be blocked until the
635probe is concluded).
636
637
638====================
639EXAMPLE SERVER USAGE
640====================
641
642A server would be set up to accept operations in the following manner:
643
644 (1) An RxRPC socket is created by:
645
646 server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
647
648 Where the third parameter indicates the address type of the transport
649 socket used - usually IPv4.
650
651 (2) Security is set up if desired by giving the socket a keyring with server
652 secret keys in it:
653
654 keyring = add_key("keyring", "AFSkeys", NULL, 0,
655 KEY_SPEC_PROCESS_KEYRING);
656
657 const char secret_key[8] = {
658 0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 };
659 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
660
661 setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7);
662
663 The keyring can be manipulated after it has been given to the socket. This
664 permits the server to add more keys, replace keys, etc. whilst it is live.
665
666 (3) A local address must then be bound:
667
668 struct sockaddr_rxrpc srx = {
669 .srx_family = AF_RXRPC,
670 .srx_service = VL_SERVICE_ID, /* RxRPC service ID */
671 .transport_type = SOCK_DGRAM, /* type of transport socket */
672 .transport.sin_family = AF_INET,
673 .transport.sin_port = htons(7000), /* AFS callback */
674 .transport.sin_address = 0, /* all local interfaces */
675 };
676 bind(server, &srx, sizeof(srx));
677
678 More than one service ID may be bound to a socket, provided the transport
679 parameters are the same. The limit is currently two. To do this, bind()
680 should be called twice.
681
682 (4) If service upgrading is required, first two service IDs must have been
683 bound and then the following option must be set:
684
685 unsigned short service_ids[2] = { from_ID, to_ID };
686 setsockopt(server, SOL_RXRPC, RXRPC_UPGRADEABLE_SERVICE,
687 service_ids, sizeof(service_ids));
688
689 This will automatically upgrade connections on service from_ID to service
690 to_ID if they request it. This will be reflected in msg_name obtained
691 through recvmsg() when the request data is delivered to userspace.
692
693 (5) The server is then set to listen out for incoming calls:
694
695 listen(server, 100);
696
697 (6) The kernel notifies the server of pending incoming connections by sending
698 it a message for each. This is received with recvmsg() on the server
699 socket. It has no data, and has a single dataless control message
700 attached:
701
702 RXRPC_NEW_CALL
703
704 The address that can be passed back by recvmsg() at this point should be
705 ignored since the call for which the message was posted may have gone by
706 the time it is accepted - in which case the first call still on the queue
707 will be accepted.
708
709 (7) The server then accepts the new call by issuing a sendmsg() with two
710 pieces of control data and no actual data:
711
712 RXRPC_ACCEPT - indicate connection acceptance
713 RXRPC_USER_CALL_ID - specify user ID for this call
714
715 (8) The first request data packet will then be posted to the server socket for
716 recvmsg() to pick up. At that point, the RxRPC address for the call can
717 be read from the address fields in the msghdr struct.
718
719 Subsequent request data will be posted to the server socket for recvmsg()
720 to collect as it arrives. All but the last piece of the request data will
721 be delivered with MSG_MORE flagged.
722
723 All data will be delivered with the following control message attached:
724
725 RXRPC_USER_CALL_ID - specifies the user ID for this call
726
727 (9) The reply data should then be posted to the server socket using a series
728 of sendmsg() calls, each with the following control messages attached:
729
730 RXRPC_USER_CALL_ID - specifies the user ID for this call
731
732 MSG_MORE should be set in msghdr::msg_flags on all but the last message
733 for a particular call.
734
735(10) The final ACK from the client will be posted for retrieval by recvmsg()
736 when it is received. It will take the form of a dataless message with two
737 control messages attached:
738
739 RXRPC_USER_CALL_ID - specifies the user ID for this call
740 RXRPC_ACK - indicates final ACK (no data)
741
742 MSG_EOR will be flagged to indicate that this is the final message for
743 this call.
744
745(11) Up to the point the final packet of reply data is sent, the call can be
746 aborted by calling sendmsg() with a dataless message with the following
747 control messages attached:
748
749 RXRPC_USER_CALL_ID - specifies the user ID for this call
750 RXRPC_ABORT - indicates abort code (4 byte data)
751
752 Any packets waiting in the socket's receive queue will be discarded if
753 this is issued.
754
755Note that all the communications for a particular service take place through
756the one server socket, using control messages on sendmsg() and recvmsg() to
757determine the call affected.
758
759
760=========================
761AF_RXRPC KERNEL INTERFACE
762=========================
763
764The AF_RXRPC module also provides an interface for use by in-kernel utilities
765such as the AFS filesystem. This permits such a utility to:
766
767 (1) Use different keys directly on individual client calls on one socket
768 rather than having to open a whole slew of sockets, one for each key it
769 might want to use.
770
771 (2) Avoid having RxRPC call request_key() at the point of issue of a call or
772 opening of a socket. Instead the utility is responsible for requesting a
773 key at the appropriate point. AFS, for instance, would do this during VFS
774 operations such as open() or unlink(). The key is then handed through
775 when the call is initiated.
776
777 (3) Request the use of something other than GFP_KERNEL to allocate memory.
778
779 (4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be
780 intercepted before they get put into the socket Rx queue and the socket
781 buffers manipulated directly.
782
783To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,
784bind an address as appropriate and listen if it's to be a server socket, but
785then it passes this to the kernel interface functions.
786
787The kernel interface functions are as follows:
788
789 (*) Begin a new client call.
790
791 struct rxrpc_call *
792 rxrpc_kernel_begin_call(struct socket *sock,
793 struct sockaddr_rxrpc *srx,
794 struct key *key,
795 unsigned long user_call_ID,
796 s64 tx_total_len,
797 gfp_t gfp,
798 rxrpc_notify_rx_t notify_rx,
799 bool upgrade);
800
801 This allocates the infrastructure to make a new RxRPC call and assigns
802 call and connection numbers. The call will be made on the UDP port that
803 the socket is bound to. The call will go to the destination address of a
804 connected client socket unless an alternative is supplied (srx is
805 non-NULL).
806
807 If a key is supplied then this will be used to secure the call instead of
808 the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls
809 secured in this way will still share connections if at all possible.
810
811 The user_call_ID is equivalent to that supplied to sendmsg() in the
812 control data buffer. It is entirely feasible to use this to point to a
813 kernel data structure.
814
815 tx_total_len is the amount of data the caller is intending to transmit
816 with this call (or -1 if unknown at this point). Setting the data size
817 allows the kernel to encrypt directly to the packet buffers, thereby
818 saving a copy. The value may not be less than -1.
819
820 notify_rx is a pointer to a function to be called when events such as
821 incoming data packets or remote aborts happen.
822
823 upgrade should be set to true if a client operation should request that
824 the server upgrade the service to a better one. The resultant service ID
825 is returned by rxrpc_kernel_recv_data().
826
827 If this function is successful, an opaque reference to the RxRPC call is
828 returned. The caller now holds a reference on this and it must be
829 properly ended.
830
831 (*) End a client call.
832
833 void rxrpc_kernel_end_call(struct socket *sock,
834 struct rxrpc_call *call);
835
836 This is used to end a previously begun call. The user_call_ID is expunged
837 from AF_RXRPC's knowledge and will not be seen again in association with
838 the specified call.
839
840 (*) Send data through a call.
841
842 typedef void (*rxrpc_notify_end_tx_t)(struct sock *sk,
843 unsigned long user_call_ID,
844 struct sk_buff *skb);
845
846 int rxrpc_kernel_send_data(struct socket *sock,
847 struct rxrpc_call *call,
848 struct msghdr *msg,
849 size_t len,
850 rxrpc_notify_end_tx_t notify_end_rx);
851
852 This is used to supply either the request part of a client call or the
853 reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the
854 data buffers to be used. msg_iov may not be NULL and must point
855 exclusively to in-kernel virtual addresses. msg.msg_flags may be given
856 MSG_MORE if there will be subsequent data sends for this call.
857
858 The msg must not specify a destination address, control data or any flags
859 other than MSG_MORE. len is the total amount of data to transmit.
860
861 notify_end_rx can be NULL or it can be used to specify a function to be
862 called when the call changes state to end the Tx phase. This function is
863 called with the call-state spinlock held to prevent any reply or final ACK
864 from being delivered first.
865
866 (*) Receive data from a call.
867
868 int rxrpc_kernel_recv_data(struct socket *sock,
869 struct rxrpc_call *call,
870 void *buf,
871 size_t size,
872 size_t *_offset,
873 bool want_more,
874 u32 *_abort,
875 u16 *_service)
876
877 This is used to receive data from either the reply part of a client call
878 or the request part of a service call. buf and size specify how much
879 data is desired and where to store it. *_offset is added on to buf and
880 subtracted from size internally; the amount copied into the buffer is
881 added to *_offset before returning.
882
883 want_more should be true if further data will be required after this is
884 satisfied and false if this is the last item of the receive phase.
885
886 There are three normal returns: 0 if the buffer was filled and want_more
887 was true; 1 if the buffer was filled, the last DATA packet has been
888 emptied and want_more was false; and -EAGAIN if the function needs to be
889 called again.
890
891 If the last DATA packet is processed but the buffer contains less than
892 the amount requested, EBADMSG is returned. If want_more wasn't set, but
893 more data was available, EMSGSIZE is returned.
894
895 If a remote ABORT is detected, the abort code received will be stored in
896 *_abort and ECONNABORTED will be returned.
897
898 The service ID that the call ended up with is returned into *_service.
899 This can be used to see if a call got a service upgrade.
900
901 (*) Abort a call.
902
903 void rxrpc_kernel_abort_call(struct socket *sock,
904 struct rxrpc_call *call,
905 u32 abort_code);
906
907 This is used to abort a call if it's still in an abortable state. The
908 abort code specified will be placed in the ABORT message sent.
909
910 (*) Intercept received RxRPC messages.
911
912 typedef void (*rxrpc_interceptor_t)(struct sock *sk,
913 unsigned long user_call_ID,
914 struct sk_buff *skb);
915
916 void
917 rxrpc_kernel_intercept_rx_messages(struct socket *sock,
918 rxrpc_interceptor_t interceptor);
919
920 This installs an interceptor function on the specified AF_RXRPC socket.
921 All messages that would otherwise wind up in the socket's Rx queue are
922 then diverted to this function. Note that care must be taken to process
923 the messages in the right order to maintain DATA message sequentiality.
924
925 The interceptor function itself is provided with the address of the socket
926 and handling the incoming message, the ID assigned by the kernel utility
927 to the call and the socket buffer containing the message.
928
929 The skb->mark field indicates the type of message:
930
931 MARK MEANING
932 =============================== =======================================
933 RXRPC_SKB_MARK_DATA Data message
934 RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call
935 RXRPC_SKB_MARK_BUSY Client call rejected as server busy
936 RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer
937 RXRPC_SKB_MARK_NET_ERROR Network error detected
938 RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered
939 RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance
940
941 The remote abort message can be probed with rxrpc_kernel_get_abort_code().
942 The two error messages can be probed with rxrpc_kernel_get_error_number().
943 A new call can be accepted with rxrpc_kernel_accept_call().
944
945 Data messages can have their contents extracted with the usual bunch of
946 socket buffer manipulation functions. A data message can be determined to
947 be the last one in a sequence with rxrpc_kernel_is_data_last(). When a
948 data message has been used up, rxrpc_kernel_data_consumed() should be
949 called on it.
950
951 Messages should be handled to rxrpc_kernel_free_skb() to dispose of. It
952 is possible to get extra refs on all types of message for later freeing,
953 but this may pin the state of a call until the message is finally freed.
954
955 (*) Accept an incoming call.
956
957 struct rxrpc_call *
958 rxrpc_kernel_accept_call(struct socket *sock,
959 unsigned long user_call_ID);
960
961 This is used to accept an incoming call and to assign it a call ID. This
962 function is similar to rxrpc_kernel_begin_call() and calls accepted must
963 be ended in the same way.
964
965 If this function is successful, an opaque reference to the RxRPC call is
966 returned. The caller now holds a reference on this and it must be
967 properly ended.
968
969 (*) Reject an incoming call.
970
971 int rxrpc_kernel_reject_call(struct socket *sock);
972
973 This is used to reject the first incoming call on the socket's queue with
974 a BUSY message. -ENODATA is returned if there were no incoming calls.
975 Other errors may be returned if the call had been aborted (-ECONNABORTED)
976 or had timed out (-ETIME).
977
978 (*) Allocate a null key for doing anonymous security.
979
980 struct key *rxrpc_get_null_key(const char *keyname);
981
982 This is used to allocate a null RxRPC key that can be used to indicate
983 anonymous security for a particular domain.
984
985 (*) Get the peer address of a call.
986
987 void rxrpc_kernel_get_peer(struct socket *sock, struct rxrpc_call *call,
988 struct sockaddr_rxrpc *_srx);
989
990 This is used to find the remote peer address of a call.
991
992 (*) Set the total transmit data size on a call.
993
994 void rxrpc_kernel_set_tx_length(struct socket *sock,
995 struct rxrpc_call *call,
996 s64 tx_total_len);
997
998 This sets the amount of data that the caller is intending to transmit on a
999 call. It's intended to be used for setting the reply size as the request
1000 size should be set when the call is begun. tx_total_len may not be less
1001 than zero.
1002
1003 (*) Check to see the completion state of a call so that the caller can assess
1004 whether it needs to be retried.
1005
1006 enum rxrpc_call_completion {
1007 RXRPC_CALL_SUCCEEDED,
1008 RXRPC_CALL_REMOTELY_ABORTED,
1009 RXRPC_CALL_LOCALLY_ABORTED,
1010 RXRPC_CALL_LOCAL_ERROR,
1011 RXRPC_CALL_NETWORK_ERROR,
1012 };
1013
1014 int rxrpc_kernel_check_call(struct socket *sock, struct rxrpc_call *call,
1015 enum rxrpc_call_completion *_compl,
1016 u32 *_abort_code);
1017
1018 On return, -EINPROGRESS will be returned if the call is still ongoing; if
1019 it is finished, *_compl will be set to indicate the manner of completion,
1020 *_abort_code will be set to any abort code that occurred. 0 will be
1021 returned on a successful completion, -ECONNABORTED will be returned if the
1022 client failed due to a remote abort and anything else will return an
1023 appropriate error code.
1024
1025 The caller should look at this information to decide if it's worth
1026 retrying the call.
1027
1028 (*) Retry a client call.
1029
1030 int rxrpc_kernel_retry_call(struct socket *sock,
1031 struct rxrpc_call *call,
1032 struct sockaddr_rxrpc *srx,
1033 struct key *key);
1034
1035 This attempts to partially reinitialise a call and submit it again whilst
1036 reusing the original call's Tx queue to avoid the need to repackage and
1037 re-encrypt the data to be sent. call indicates the call to retry, srx the
1038 new address to send it to and key the encryption key to use for signing or
1039 encrypting the packets.
1040
1041 For this to work, the first Tx data packet must still be in the transmit
1042 queue, and currently this is only permitted for local and network errors
1043 and the call must not have been aborted. Any partially constructed Tx
1044 packet is left as is and can continue being filled afterwards.
1045
1046 It returns 0 if the call was requeued and an error otherwise.
1047
1048 (*) Get call RTT.
1049
1050 u64 rxrpc_kernel_get_rtt(struct socket *sock, struct rxrpc_call *call);
1051
1052 Get the RTT time to the peer in use by a call. The value returned is in
1053 nanoseconds.
1054
1055 (*) Check call still alive.
1056
1057 u32 rxrpc_kernel_check_life(struct socket *sock,
1058 struct rxrpc_call *call);
1059
1060 This returns a number that is updated when ACKs are received from the peer
1061 (notably including PING RESPONSE ACKs which we can elicit by sending PING
1062 ACKs to see if the call still exists on the server). The caller should
1063 compare the numbers of two calls to see if the call is still alive after
1064 waiting for a suitable interval.
1065
1066 This allows the caller to work out if the server is still contactable and
1067 if the call is still alive on the server whilst waiting for the server to
1068 process a client operation.
1069
1070 This function may transmit a PING ACK.
1071
1072
1073=======================
1074CONFIGURABLE PARAMETERS
1075=======================
1076
1077The RxRPC protocol driver has a number of configurable parameters that can be
1078adjusted through sysctls in /proc/net/rxrpc/:
1079
1080 (*) req_ack_delay
1081
1082 The amount of time in milliseconds after receiving a packet with the
1083 request-ack flag set before we honour the flag and actually send the
1084 requested ack.
1085
1086 Usually the other side won't stop sending packets until the advertised
1087 reception window is full (to a maximum of 255 packets), so delaying the
1088 ACK permits several packets to be ACK'd in one go.
1089
1090 (*) soft_ack_delay
1091
1092 The amount of time in milliseconds after receiving a new packet before we
1093 generate a soft-ACK to tell the sender that it doesn't need to resend.
1094
1095 (*) idle_ack_delay
1096
1097 The amount of time in milliseconds after all the packets currently in the
1098 received queue have been consumed before we generate a hard-ACK to tell
1099 the sender it can free its buffers, assuming no other reason occurs that
1100 we would send an ACK.
1101
1102 (*) resend_timeout
1103
1104 The amount of time in milliseconds after transmitting a packet before we
1105 transmit it again, assuming no ACK is received from the receiver telling
1106 us they got it.
1107
1108 (*) max_call_lifetime
1109
1110 The maximum amount of time in seconds that a call may be in progress
1111 before we preemptively kill it.
1112
1113 (*) dead_call_expiry
1114
1115 The amount of time in seconds before we remove a dead call from the call
1116 list. Dead calls are kept around for a little while for the purpose of
1117 repeating ACK and ABORT packets.
1118
1119 (*) connection_expiry
1120
1121 The amount of time in seconds after a connection was last used before we
1122 remove it from the connection list. Whilst a connection is in existence,
1123 it serves as a placeholder for negotiated security; when it is deleted,
1124 the security must be renegotiated.
1125
1126 (*) transport_expiry
1127
1128 The amount of time in seconds after a transport was last used before we
1129 remove it from the transport list. Whilst a transport is in existence, it
1130 serves to anchor the peer data and keeps the connection ID counter.
1131
1132 (*) rxrpc_rx_window_size
1133
1134 The size of the receive window in packets. This is the maximum number of
1135 unconsumed received packets we're willing to hold in memory for any
1136 particular call.
1137
1138 (*) rxrpc_rx_mtu
1139
1140 The maximum packet MTU size that we're willing to receive in bytes. This
1141 indicates to the peer whether we're willing to accept jumbo packets.
1142
1143 (*) rxrpc_rx_jumbo_max
1144
1145 The maximum number of packets that we're willing to accept in a jumbo
1146 packet. Non-terminal packets in a jumbo packet must contain a four byte
1147 header plus exactly 1412 bytes of data. The terminal packet must contain
1148 a four byte header plus any amount of data. In any event, a jumbo packet
1149 may not exceed rxrpc_rx_mtu in size.