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David Howells17926a72007-04-26 15:48:28 -07001 ======================
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
David Howells651350d2007-04-26 15:50:17 -070028 (*) AF_RXRPC kernel interface.
29
David Howells5873c082014-02-07 18:58:44 +000030 (*) Configurable parameters.
31
David Howells17926a72007-04-26 15:48:28 -070032
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
Masanari Iidac17cb8b2013-10-30 16:46:15 +0900149 (*) There are two types of positive acknowledgment: hard-ACKs and soft-ACKs.
David Howells17926a72007-04-26 15:48:28 -0700150 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 recvmsg:
284
285 (*) If there's a sequence of data messages belonging to a particular call on
286 the receive queue, then recvmsg will keep working through them until:
287
288 (a) it meets the end of that call's received data,
289
290 (b) it meets a non-data message,
291
292 (c) it meets a message belonging to a different call, or
293
294 (d) it fills the user buffer.
295
296 If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
297 reception of further data, until one of the above four conditions is met.
298
299 (2) MSG_PEEK operates similarly, but will return immediately if it has put any
300 data in the buffer rather than sleeping until it can fill the buffer.
301
302 (3) If a data message is only partially consumed in filling a user buffer,
303 then the remainder of that message will be left on the front of the queue
304 for the next taker. MSG_TRUNC will never be flagged.
305
306 (4) If there is more data to be had on a call (it hasn't copied the last byte
307 of the last data message in that phase yet), then MSG_MORE will be
308 flagged.
309
310
311================
312CONTROL MESSAGES
313================
314
315AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
316calls, to invoke certain actions and to report certain conditions. These are:
317
318 MESSAGE ID SRT DATA MEANING
319 ======================= === =========== ===============================
320 RXRPC_USER_CALL_ID sr- User ID App's call specifier
321 RXRPC_ABORT srt Abort code Abort code to issue/received
322 RXRPC_ACK -rt n/a Final ACK received
323 RXRPC_NET_ERROR -rt error num Network error on call
324 RXRPC_BUSY -rt n/a Call rejected (server busy)
325 RXRPC_LOCAL_ERROR -rt error num Local error encountered
326 RXRPC_NEW_CALL -r- n/a New call received
327 RXRPC_ACCEPT s-- n/a Accept new call
328
329 (SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
330
331 (*) RXRPC_USER_CALL_ID
332
333 This is used to indicate the application's call ID. It's an unsigned long
334 that the app specifies in the client by attaching it to the first data
335 message or in the server by passing it in association with an RXRPC_ACCEPT
336 message. recvmsg() passes it in conjunction with all messages except
337 those of the RXRPC_NEW_CALL message.
338
339 (*) RXRPC_ABORT
340
341 This is can be used by an application to abort a call by passing it to
342 sendmsg, or it can be delivered by recvmsg to indicate a remote abort was
343 received. Either way, it must be associated with an RXRPC_USER_CALL_ID to
344 specify the call affected. If an abort is being sent, then error EBADSLT
345 will be returned if there is no call with that user ID.
346
347 (*) RXRPC_ACK
348
349 This is delivered to a server application to indicate that the final ACK
350 of a call was received from the client. It will be associated with an
351 RXRPC_USER_CALL_ID to indicate the call that's now complete.
352
353 (*) RXRPC_NET_ERROR
354
355 This is delivered to an application to indicate that an ICMP error message
356 was encountered in the process of trying to talk to the peer. An
357 errno-class integer value will be included in the control message data
358 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
359 affected.
360
361 (*) RXRPC_BUSY
362
363 This is delivered to a client application to indicate that a call was
364 rejected by the server due to the server being busy. It will be
365 associated with an RXRPC_USER_CALL_ID to indicate the rejected call.
366
367 (*) RXRPC_LOCAL_ERROR
368
369 This is delivered to an application to indicate that a local error was
370 encountered and that a call has been aborted because of it. An
371 errno-class integer value will be included in the control message data
372 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call
373 affected.
374
375 (*) RXRPC_NEW_CALL
376
377 This is delivered to indicate to a server application that a new call has
378 arrived and is awaiting acceptance. No user ID is associated with this,
379 as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT.
380
381 (*) RXRPC_ACCEPT
382
383 This is used by a server application to attempt to accept a call and
384 assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID
385 to indicate the user ID to be assigned. If there is no call to be
386 accepted (it may have timed out, been aborted, etc.), then sendmsg will
387 return error ENODATA. If the user ID is already in use by another call,
388 then error EBADSLT will be returned.
389
390
391==============
392SOCKET OPTIONS
393==============
394
395AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:
396
397 (*) RXRPC_SECURITY_KEY
398
399 This is used to specify the description of the key to be used. The key is
400 extracted from the calling process's keyrings with request_key() and
401 should be of "rxrpc" type.
402
403 The optval pointer points to the description string, and optlen indicates
404 how long the string is, without the NUL terminator.
405
406 (*) RXRPC_SECURITY_KEYRING
407
408 Similar to above but specifies a keyring of server secret keys to use (key
409 type "keyring"). See the "Security" section.
410
411 (*) RXRPC_EXCLUSIVE_CONNECTION
412
413 This is used to request that new connections should be used for each call
414 made subsequently on this socket. optval should be NULL and optlen 0.
415
416 (*) RXRPC_MIN_SECURITY_LEVEL
417
418 This is used to specify the minimum security level required for calls on
419 this socket. optval must point to an int containing one of the following
420 values:
421
422 (a) RXRPC_SECURITY_PLAIN
423
424 Encrypted checksum only.
425
426 (b) RXRPC_SECURITY_AUTH
427
428 Encrypted checksum plus packet padded and first eight bytes of packet
429 encrypted - which includes the actual packet length.
430
431 (c) RXRPC_SECURITY_ENCRYPTED
432
433 Encrypted checksum plus entire packet padded and encrypted, including
434 actual packet length.
435
436
437========
438SECURITY
439========
440
441Currently, only the kerberos 4 equivalent protocol has been implemented
442(security index 2 - rxkad). This requires the rxkad module to be loaded and,
443on the client, tickets of the appropriate type to be obtained from the AFS
444kaserver or the kerberos server and installed as "rxrpc" type keys. This is
445normally done using the klog program. An example simple klog program can be
446found at:
447
448 http://people.redhat.com/~dhowells/rxrpc/klog.c
449
450The payload provided to add_key() on the client should be of the following
451form:
452
453 struct rxrpc_key_sec2_v1 {
454 uint16_t security_index; /* 2 */
455 uint16_t ticket_length; /* length of ticket[] */
456 uint32_t expiry; /* time at which expires */
457 uint8_t kvno; /* key version number */
458 uint8_t __pad[3];
459 uint8_t session_key[8]; /* DES session key */
460 uint8_t ticket[0]; /* the encrypted ticket */
461 };
462
463Where the ticket blob is just appended to the above structure.
464
465
466For the server, keys of type "rxrpc_s" must be made available to the server.
467They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an
468rxkad key for the AFS VL service). When such a key is created, it should be
469given the server's secret key as the instantiation data (see the example
470below).
471
472 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
473
474A keyring is passed to the server socket by naming it in a sockopt. The server
475socket then looks the server secret keys up in this keyring when secure
476incoming connections are made. This can be seen in an example program that can
477be found at:
478
479 http://people.redhat.com/~dhowells/rxrpc/listen.c
480
481
482====================
483EXAMPLE CLIENT USAGE
484====================
485
486A client would issue an operation by:
487
488 (1) An RxRPC socket is set up by:
489
490 client = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
491
492 Where the third parameter indicates the protocol family of the transport
493 socket used - usually IPv4 but it can also be IPv6 [TODO].
494
495 (2) A local address can optionally be bound:
496
497 struct sockaddr_rxrpc srx = {
498 .srx_family = AF_RXRPC,
499 .srx_service = 0, /* we're a client */
500 .transport_type = SOCK_DGRAM, /* type of transport socket */
501 .transport.sin_family = AF_INET,
502 .transport.sin_port = htons(7000), /* AFS callback */
503 .transport.sin_address = 0, /* all local interfaces */
504 };
505 bind(client, &srx, sizeof(srx));
506
507 This specifies the local UDP port to be used. If not given, a random
508 non-privileged port will be used. A UDP port may be shared between
509 several unrelated RxRPC sockets. Security is handled on a basis of
510 per-RxRPC virtual connection.
511
512 (3) The security is set:
513
514 const char *key = "AFS:cambridge.redhat.com";
515 setsockopt(client, SOL_RXRPC, RXRPC_SECURITY_KEY, key, strlen(key));
516
517 This issues a request_key() to get the key representing the security
518 context. The minimum security level can be set:
519
520 unsigned int sec = RXRPC_SECURITY_ENCRYPTED;
521 setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL,
522 &sec, sizeof(sec));
523
524 (4) The server to be contacted can then be specified (alternatively this can
525 be done through sendmsg):
526
527 struct sockaddr_rxrpc srx = {
528 .srx_family = AF_RXRPC,
529 .srx_service = VL_SERVICE_ID,
530 .transport_type = SOCK_DGRAM, /* type of transport socket */
531 .transport.sin_family = AF_INET,
532 .transport.sin_port = htons(7005), /* AFS volume manager */
533 .transport.sin_address = ...,
534 };
535 connect(client, &srx, sizeof(srx));
536
537 (5) The request data should then be posted to the server socket using a series
538 of sendmsg() calls, each with the following control message attached:
539
540 RXRPC_USER_CALL_ID - specifies the user ID for this call
541
542 MSG_MORE should be set in msghdr::msg_flags on all but the last part of
543 the request. Multiple requests may be made simultaneously.
544
Frederik Schwarzer025dfda2008-10-16 19:02:37 +0200545 If a call is intended to go to a destination other than the default
David Howells17926a72007-04-26 15:48:28 -0700546 specified through connect(), then msghdr::msg_name should be set on the
547 first request message of that call.
548
549 (6) The reply data will then be posted to the server socket for recvmsg() to
550 pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data
551 for a particular call to be read. MSG_EOR will be set on the terminal
552 read for a call.
553
554 All data will be delivered with the following control message attached:
555
556 RXRPC_USER_CALL_ID - specifies the user ID for this call
557
558 If an abort or error occurred, this will be returned in the control data
559 buffer instead, and MSG_EOR will be flagged to indicate the end of that
560 call.
561
562
563====================
564EXAMPLE SERVER USAGE
565====================
566
567A server would be set up to accept operations in the following manner:
568
569 (1) An RxRPC socket is created by:
570
571 server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
572
573 Where the third parameter indicates the address type of the transport
574 socket used - usually IPv4.
575
576 (2) Security is set up if desired by giving the socket a keyring with server
577 secret keys in it:
578
579 keyring = add_key("keyring", "AFSkeys", NULL, 0,
580 KEY_SPEC_PROCESS_KEYRING);
581
582 const char secret_key[8] = {
583 0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 };
584 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
585
586 setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7);
587
588 The keyring can be manipulated after it has been given to the socket. This
589 permits the server to add more keys, replace keys, etc. whilst it is live.
590
591 (2) A local address must then be bound:
592
593 struct sockaddr_rxrpc srx = {
594 .srx_family = AF_RXRPC,
595 .srx_service = VL_SERVICE_ID, /* RxRPC service ID */
596 .transport_type = SOCK_DGRAM, /* type of transport socket */
597 .transport.sin_family = AF_INET,
598 .transport.sin_port = htons(7000), /* AFS callback */
599 .transport.sin_address = 0, /* all local interfaces */
600 };
601 bind(server, &srx, sizeof(srx));
602
603 (3) The server is then set to listen out for incoming calls:
604
605 listen(server, 100);
606
607 (4) The kernel notifies the server of pending incoming connections by sending
608 it a message for each. This is received with recvmsg() on the server
609 socket. It has no data, and has a single dataless control message
610 attached:
611
612 RXRPC_NEW_CALL
613
614 The address that can be passed back by recvmsg() at this point should be
615 ignored since the call for which the message was posted may have gone by
616 the time it is accepted - in which case the first call still on the queue
617 will be accepted.
618
619 (5) The server then accepts the new call by issuing a sendmsg() with two
620 pieces of control data and no actual data:
621
622 RXRPC_ACCEPT - indicate connection acceptance
623 RXRPC_USER_CALL_ID - specify user ID for this call
624
625 (6) The first request data packet will then be posted to the server socket for
626 recvmsg() to pick up. At that point, the RxRPC address for the call can
627 be read from the address fields in the msghdr struct.
628
629 Subsequent request data will be posted to the server socket for recvmsg()
630 to collect as it arrives. All but the last piece of the request data will
631 be delivered with MSG_MORE flagged.
632
633 All data will be delivered with the following control message attached:
634
635 RXRPC_USER_CALL_ID - specifies the user ID for this call
636
637 (8) The reply data should then be posted to the server socket using a series
638 of sendmsg() calls, each with the following control messages attached:
639
640 RXRPC_USER_CALL_ID - specifies the user ID for this call
641
642 MSG_MORE should be set in msghdr::msg_flags on all but the last message
643 for a particular call.
644
645 (9) The final ACK from the client will be posted for retrieval by recvmsg()
646 when it is received. It will take the form of a dataless message with two
647 control messages attached:
648
649 RXRPC_USER_CALL_ID - specifies the user ID for this call
650 RXRPC_ACK - indicates final ACK (no data)
651
652 MSG_EOR will be flagged to indicate that this is the final message for
653 this call.
654
655(10) Up to the point the final packet of reply data is sent, the call can be
656 aborted by calling sendmsg() with a dataless message with the following
657 control messages attached:
658
659 RXRPC_USER_CALL_ID - specifies the user ID for this call
660 RXRPC_ABORT - indicates abort code (4 byte data)
661
662 Any packets waiting in the socket's receive queue will be discarded if
663 this is issued.
664
665Note that all the communications for a particular service take place through
666the one server socket, using control messages on sendmsg() and recvmsg() to
667determine the call affected.
David Howells651350d2007-04-26 15:50:17 -0700668
669
670=========================
671AF_RXRPC KERNEL INTERFACE
672=========================
673
674The AF_RXRPC module also provides an interface for use by in-kernel utilities
675such as the AFS filesystem. This permits such a utility to:
676
677 (1) Use different keys directly on individual client calls on one socket
678 rather than having to open a whole slew of sockets, one for each key it
679 might want to use.
680
681 (2) Avoid having RxRPC call request_key() at the point of issue of a call or
682 opening of a socket. Instead the utility is responsible for requesting a
683 key at the appropriate point. AFS, for instance, would do this during VFS
684 operations such as open() or unlink(). The key is then handed through
685 when the call is initiated.
686
687 (3) Request the use of something other than GFP_KERNEL to allocate memory.
688
689 (4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be
690 intercepted before they get put into the socket Rx queue and the socket
691 buffers manipulated directly.
692
693To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,
Matt LaPlante01dd2fb2007-10-20 01:34:40 +0200694bind an address as appropriate and listen if it's to be a server socket, but
David Howells651350d2007-04-26 15:50:17 -0700695then it passes this to the kernel interface functions.
696
697The kernel interface functions are as follows:
698
699 (*) Begin a new client call.
700
701 struct rxrpc_call *
702 rxrpc_kernel_begin_call(struct socket *sock,
703 struct sockaddr_rxrpc *srx,
704 struct key *key,
705 unsigned long user_call_ID,
706 gfp_t gfp);
707
708 This allocates the infrastructure to make a new RxRPC call and assigns
709 call and connection numbers. The call will be made on the UDP port that
710 the socket is bound to. The call will go to the destination address of a
711 connected client socket unless an alternative is supplied (srx is
712 non-NULL).
713
714 If a key is supplied then this will be used to secure the call instead of
715 the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls
716 secured in this way will still share connections if at all possible.
717
718 The user_call_ID is equivalent to that supplied to sendmsg() in the
719 control data buffer. It is entirely feasible to use this to point to a
720 kernel data structure.
721
722 If this function is successful, an opaque reference to the RxRPC call is
723 returned. The caller now holds a reference on this and it must be
724 properly ended.
725
726 (*) End a client call.
727
728 void rxrpc_kernel_end_call(struct rxrpc_call *call);
729
730 This is used to end a previously begun call. The user_call_ID is expunged
731 from AF_RXRPC's knowledge and will not be seen again in association with
732 the specified call.
733
734 (*) Send data through a call.
735
736 int rxrpc_kernel_send_data(struct rxrpc_call *call, struct msghdr *msg,
737 size_t len);
738
739 This is used to supply either the request part of a client call or the
740 reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the
741 data buffers to be used. msg_iov may not be NULL and must point
742 exclusively to in-kernel virtual addresses. msg.msg_flags may be given
743 MSG_MORE if there will be subsequent data sends for this call.
744
745 The msg must not specify a destination address, control data or any flags
746 other than MSG_MORE. len is the total amount of data to transmit.
747
748 (*) Abort a call.
749
750 void rxrpc_kernel_abort_call(struct rxrpc_call *call, u32 abort_code);
751
752 This is used to abort a call if it's still in an abortable state. The
753 abort code specified will be placed in the ABORT message sent.
754
755 (*) Intercept received RxRPC messages.
756
757 typedef void (*rxrpc_interceptor_t)(struct sock *sk,
758 unsigned long user_call_ID,
759 struct sk_buff *skb);
760
761 void
762 rxrpc_kernel_intercept_rx_messages(struct socket *sock,
763 rxrpc_interceptor_t interceptor);
764
765 This installs an interceptor function on the specified AF_RXRPC socket.
766 All messages that would otherwise wind up in the socket's Rx queue are
767 then diverted to this function. Note that care must be taken to process
768 the messages in the right order to maintain DATA message sequentiality.
769
770 The interceptor function itself is provided with the address of the socket
771 and handling the incoming message, the ID assigned by the kernel utility
772 to the call and the socket buffer containing the message.
773
774 The skb->mark field indicates the type of message:
775
776 MARK MEANING
777 =============================== =======================================
778 RXRPC_SKB_MARK_DATA Data message
779 RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call
780 RXRPC_SKB_MARK_BUSY Client call rejected as server busy
781 RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer
782 RXRPC_SKB_MARK_NET_ERROR Network error detected
783 RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered
784 RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance
785
786 The remote abort message can be probed with rxrpc_kernel_get_abort_code().
787 The two error messages can be probed with rxrpc_kernel_get_error_number().
788 A new call can be accepted with rxrpc_kernel_accept_call().
789
790 Data messages can have their contents extracted with the usual bunch of
791 socket buffer manipulation functions. A data message can be determined to
792 be the last one in a sequence with rxrpc_kernel_is_data_last(). When a
793 data message has been used up, rxrpc_kernel_data_delivered() should be
794 called on it..
795
796 Non-data messages should be handled to rxrpc_kernel_free_skb() to dispose
797 of. It is possible to get extra refs on all types of message for later
798 freeing, but this may pin the state of a call until the message is finally
799 freed.
800
801 (*) Accept an incoming call.
802
803 struct rxrpc_call *
804 rxrpc_kernel_accept_call(struct socket *sock,
805 unsigned long user_call_ID);
806
807 This is used to accept an incoming call and to assign it a call ID. This
808 function is similar to rxrpc_kernel_begin_call() and calls accepted must
809 be ended in the same way.
810
811 If this function is successful, an opaque reference to the RxRPC call is
812 returned. The caller now holds a reference on this and it must be
813 properly ended.
814
815 (*) Reject an incoming call.
816
817 int rxrpc_kernel_reject_call(struct socket *sock);
818
819 This is used to reject the first incoming call on the socket's queue with
820 a BUSY message. -ENODATA is returned if there were no incoming calls.
821 Other errors may be returned if the call had been aborted (-ECONNABORTED)
822 or had timed out (-ETIME).
823
824 (*) Record the delivery of a data message and free it.
825
826 void rxrpc_kernel_data_delivered(struct sk_buff *skb);
827
828 This is used to record a data message as having been delivered and to
829 update the ACK state for the call. The socket buffer will be freed.
830
831 (*) Free a message.
832
833 void rxrpc_kernel_free_skb(struct sk_buff *skb);
834
835 This is used to free a non-DATA socket buffer intercepted from an AF_RXRPC
836 socket.
837
838 (*) Determine if a data message is the last one on a call.
839
840 bool rxrpc_kernel_is_data_last(struct sk_buff *skb);
841
842 This is used to determine if a socket buffer holds the last data message
843 to be received for a call (true will be returned if it does, false
844 if not).
845
846 The data message will be part of the reply on a client call and the
847 request on an incoming call. In the latter case there will be more
848 messages, but in the former case there will not.
849
850 (*) Get the abort code from an abort message.
851
852 u32 rxrpc_kernel_get_abort_code(struct sk_buff *skb);
853
854 This is used to extract the abort code from a remote abort message.
855
856 (*) Get the error number from a local or network error message.
857
858 int rxrpc_kernel_get_error_number(struct sk_buff *skb);
859
860 This is used to extract the error number from a message indicating either
861 a local error occurred or a network error occurred.
David Howells76181c12007-10-16 23:29:46 -0700862
863 (*) Allocate a null key for doing anonymous security.
864
865 struct key *rxrpc_get_null_key(const char *keyname);
866
867 This is used to allocate a null RxRPC key that can be used to indicate
868 anonymous security for a particular domain.
David Howells5873c082014-02-07 18:58:44 +0000869
870
871=======================
872CONFIGURABLE PARAMETERS
873=======================
874
875The RxRPC protocol driver has a number of configurable parameters that can be
876adjusted through sysctls in /proc/net/rxrpc/:
877
878 (*) req_ack_delay
879
880 The amount of time in milliseconds after receiving a packet with the
881 request-ack flag set before we honour the flag and actually send the
882 requested ack.
883
884 Usually the other side won't stop sending packets until the advertised
885 reception window is full (to a maximum of 255 packets), so delaying the
886 ACK permits several packets to be ACK'd in one go.
887
888 (*) soft_ack_delay
889
890 The amount of time in milliseconds after receiving a new packet before we
891 generate a soft-ACK to tell the sender that it doesn't need to resend.
892
893 (*) idle_ack_delay
894
895 The amount of time in milliseconds after all the packets currently in the
896 received queue have been consumed before we generate a hard-ACK to tell
897 the sender it can free its buffers, assuming no other reason occurs that
898 we would send an ACK.
899
900 (*) resend_timeout
901
902 The amount of time in milliseconds after transmitting a packet before we
903 transmit it again, assuming no ACK is received from the receiver telling
904 us they got it.
905
906 (*) max_call_lifetime
907
908 The maximum amount of time in seconds that a call may be in progress
909 before we preemptively kill it.
910
911 (*) dead_call_expiry
912
913 The amount of time in seconds before we remove a dead call from the call
914 list. Dead calls are kept around for a little while for the purpose of
915 repeating ACK and ABORT packets.
916
917 (*) connection_expiry
918
919 The amount of time in seconds after a connection was last used before we
920 remove it from the connection list. Whilst a connection is in existence,
921 it serves as a placeholder for negotiated security; when it is deleted,
922 the security must be renegotiated.
923
924 (*) transport_expiry
925
926 The amount of time in seconds after a transport was last used before we
927 remove it from the transport list. Whilst a transport is in existence, it
928 serves to anchor the peer data and keeps the connection ID counter.
David Howells817913d2014-02-07 18:10:30 +0000929
930 (*) rxrpc_rx_window_size
931
932 The size of the receive window in packets. This is the maximum number of
933 unconsumed received packets we're willing to hold in memory for any
934 particular call.
935
936 (*) rxrpc_rx_mtu
937
938 The maximum packet MTU size that we're willing to receive in bytes. This
939 indicates to the peer whether we're willing to accept jumbo packets.
940
941 (*) rxrpc_rx_jumbo_max
942
943 The maximum number of packets that we're willing to accept in a jumbo
944 packet. Non-terminal packets in a jumbo packet must contain a four byte
945 header plus exactly 1412 bytes of data. The terminal packet must contain
946 a four byte header plus any amount of data. In any event, a jumbo packet
947 may not exceed rxrpc_rx_mtu in size.