1 .. SPDX-License-Identifier: GPL-2.0
2
3 ======================
4 RxRPC Network Protocol
5 ======================
6
7 The RxRPC protocol driver provides a reliable two-phase transport on top of UDP
8 that can be used to perform RxRPC remote operations. This is done over sockets
9 of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and
10 receive data, aborts and errors.
11
12 Contents of this document:
13
14 (#) Overview.
15
16 (#) RxRPC protocol summary.
17
18 (#) AF_RXRPC driver model.
19
20 (#) Control messages.
21
22 (#) Socket options.
23
24 (#) Security.
25
26 (#) Example client usage.
27
28 (#) Example server usage.
29
30 (#) AF_RXRPC kernel interface.
31
32 (#) Configurable parameters.
33
34
35 Overview
36 ========
37
38 RxRPC is a two-layer protocol. There is a session layer which provides
39 reliable virtual connections using UDP over IPv4 (or IPv6) as the transport
40 layer, but implements a real network protocol; and there's the presentation
41 layer which renders structured data to binary blobs and back again using XDR
42 (as does SunRPC)::
43
44 +-------------+
45 | Application |
46 +-------------+
47 | XDR | Presentation
48 +-------------+
49 | RxRPC | Session
50 +-------------+
51 | UDP | Transport
52 +-------------+
53
54
55 AF_RXRPC provides:
56
57 (1) Part of an RxRPC facility for both kernel and userspace applications by
58 making the session part of it a Linux network protocol (AF_RXRPC).
59
60 (2) A two-phase protocol. The client transmits a blob (the request) and then
61 receives a blob (the reply), and the server receives the request and then
62 transmits the reply.
63
64 (3) Retention of the reusable bits of the transport system set up for one call
65 to speed up subsequent calls.
66
67 (4) A secure protocol, using the Linux kernel's key retention facility to
68 manage security on the client end. The server end must of necessity be
69 more active in security negotiations.
70
71 AF_RXRPC does not provide XDR marshalling/presentation facilities. That is
72 left to the application. AF_RXRPC only deals in blobs. Even the operation ID
73 is just the first four bytes of the request blob, and as such is beyond the
74 kernel's interest.
75
76
77 Sockets of AF_RXRPC family are:
78
79 (1) created as type SOCK_DGRAM;
80
81 (2) provided with a protocol of the type of underlying transport they're going
82 to use - currently only PF_INET is supported.
83
84
85 The Andrew File System (AFS) is an example of an application that uses this and
86 that has both kernel (filesystem) and userspace (utility) components.
87
88
89 RxRPC Protocol Summary
90 ======================
91
92 An 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 AF_RXRPC Driver Model
166 =====================
167
168 About the AF_RXRPC driver:
169
170 (#) The AF_RXRPC protocol transparently uses internal sockets of the transport
171 protocol to represent transport endpoints.
172
173 (#) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC
174 connections are handled transparently. One client socket may be used to
175 make multiple simultaneous calls to the same service. One server socket
176 may handle calls from many clients.
177
178 (#) Additional parallel client connections will be initiated to support extra
179 concurrent calls, up to a tunable limit.
180
181 (#) Each connection is retained for a certain amount of time [tunable] after
182 the last call currently using it has completed in case a new call is made
183 that could reuse it.
184
185 (#) Each internal UDP socket is retained [tunable] for a certain amount of
186 time [tunable] after the last connection using it discarded, in case a new
187 connection is made that could use it.
188
189 (#) A client-side connection is only shared between calls if they have
190 the same key struct describing their security (and assuming the calls
191 would otherwise share the connection). Non-secured calls would also be
192 able to share connections with each other.
193
194 (#) A server-side connection is shared if the client says it is.
195
196 (#) ACK'ing is handled by the protocol driver automatically, including ping
197 replying.
198
199 (#) SO_KEEPALIVE automatically pings the other side to keep the connection
200 alive [TODO].
201
202 (#) If an ICMP error is received, all calls affected by that error will be
203 aborted with an appropriate network error passed through recvmsg().
204
205
206 Interaction with the user of the RxRPC socket:
207
208 (#) A socket is made into a server socket by binding an address with a
209 non-zero service ID.
210
211 (#) In the client, sending a request is achieved with one or more sendmsgs,
212 followed by the reply being received with one or more recvmsgs.
213
214 (#) The first sendmsg for a request to be sent from a client contains a tag to
215 be used in all other sendmsgs or recvmsgs associated with that call. The
216 tag is carried in the control data.
217
218 (#) connect() is used to supply a default destination address for a client
219 socket. This may be overridden by supplying an alternate address to the
220 first sendmsg() of a call (struct msghdr::msg_name).
221
222 (#) If connect() is called on an unbound client, a random local port will
223 bound before the operation takes place.
224
225 (#) A server socket may also be used to make client calls. To do this, the
226 first sendmsg() of the call must specify the target address. The server's
227 transport endpoint is used to send the packets.
228
229 (#) Once the application has received the last message associated with a call,
230 the tag is guaranteed not to be seen again, and so it can be used to pin
231 client resources. A new call can then be initiated with the same tag
232 without fear of interference.
233
234 (#) In the server, a request is received with one or more recvmsgs, then the
235 the reply is transmitted with one or more sendmsgs, and then the final ACK
236 is received with a last recvmsg.
237
238 (#) When sending data for a call, sendmsg is given MSG_MORE if there's more
239 data to come on that call.
240
241 (#) When receiving data for a call, recvmsg flags MSG_MORE if there's more
242 data to come for that call.
243
244 (#) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg
245 to indicate the terminal message for that call.
246
247 (#) A call may be aborted by adding an abort control message to the control
248 data. Issuing an abort terminates the kernel's use of that call's tag.
249 Any messages waiting in the receive queue for that call will be discarded.
250
251 (#) Aborts, busy notifications and challenge packets are delivered by recvmsg,
252 and control data messages will be set to indicate the context. Receiving
253 an abort or a busy message terminates the kernel's use of that call's tag.
254
255 (#) The control data part of the msghdr struct is used for a number of things:
256
257 (#) The tag of the intended or affected call.
258
259 (#) Sending or receiving errors, aborts and busy notifications.
260
261 (#) Notifications of incoming calls.
262
263 (#) Sending debug requests and receiving debug replies [TODO].
264
265 (#) When the kernel has received and set up an incoming call, it sends a
266 message to server application to let it know there's a new call awaiting
267 its acceptance [recvmsg reports a special control message]. The server
268 application then uses sendmsg to assign a tag to the new call. Once that
269 is done, the first part of the request data will be delivered by recvmsg.
270
271 (#) The server application has to provide the server socket with a keyring of
272 secret keys corresponding to the security types it permits. When a secure
273 connection is being set up, the kernel looks up the appropriate secret key
274 in the keyring and then sends a challenge packet to the client and
275 receives a response packet. The kernel then checks the authorisation of
276 the packet and either aborts the connection or sets up the security.
277
278 (#) The name of the key a client will use to secure its communications is
279 nominated by a socket option.
280
281
282 Notes on sendmsg:
283
284 (#) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is
285 making progress at accepting packets within a reasonable time such that we
286 manage to queue up all the data for transmission. This requires the
287 client to accept at least one packet per 2*RTT time period.
288
289 If this isn't set, sendmsg() will return immediately, either returning
290 EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data
291 consumed.
292
293
294 Notes on recvmsg:
295
296 (#) If there's a sequence of data messages belonging to a particular call on
297 the receive queue, then recvmsg will keep working through them until:
298
299 (a) it meets the end of that call's received data,
300
301 (b) it meets a non-data message,
302
303 (c) it meets a message belonging to a different call, or
304
305 (d) it fills the user buffer.
306
307 If recvmsg is called in blocking mode, it will keep sleeping, awaiting the
308 reception of further data, until one of the above four conditions is met.
309
310 (2) MSG_PEEK operates similarly, but will return immediately if it has put any
311 data in the buffer rather than sleeping until it can fill the buffer.
312
313 (3) If a data message is only partially consumed in filling a user buffer,
314 then the remainder of that message will be left on the front of the queue
315 for the next taker. MSG_TRUNC will never be flagged.
316
317 (4) If there is more data to be had on a call (it hasn't copied the last byte
318 of the last data message in that phase yet), then MSG_MORE will be
319 flagged.
320
321
322 Control Messages
323 ================
324
325 AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex
326 calls, to invoke certain actions and to report certain conditions. These are:
327
328 ======================= === =========== ===============================
329 MESSAGE ID SRT DATA MEANING
330 ======================= === =========== ===============================
331 RXRPC_USER_CALL_ID sr- User ID App's call specifier
332 RXRPC_ABORT srt Abort code Abort code to issue/received
333 RXRPC_ACK -rt n/a Final ACK received
334 RXRPC_NET_ERROR -rt error num Network error on call
335 RXRPC_BUSY -rt n/a Call rejected (server busy)
336 RXRPC_LOCAL_ERROR -rt error num Local error encountered
337 RXRPC_NEW_CALL -r- n/a New call received
338 RXRPC_ACCEPT s-- n/a Accept new call
339 RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call
340 RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded
341 RXRPC_TX_LENGTH s-- data len Total length of Tx data
342 ======================= === =========== ===============================
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
435 The symbol RXRPC__SUPPORTED is defined as one more than the highest control
436 message type supported. At run time this can be queried by means of the
437 RXRPC_SUPPORTED_CMSG socket option (see below).
438
439
440 ==============
441 SOCKET OPTIONS
442 ==============
443
444 AF_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_ENCRYPT
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 ========
499 SECURITY
500 ========
501
502 Currently, only the kerberos 4 equivalent protocol has been implemented
503 (security index 2 - rxkad). This requires the rxkad module to be loaded and,
504 on the client, tickets of the appropriate type to be obtained from the AFS
505 kaserver or the kerberos server and installed as "rxrpc" type keys. This is
506 normally done using the klog program. An example simple klog program can be
507 found at:
508
509 http://people.redhat.com/~dhowells/rxrpc/klog.c
510
511 The payload provided to add_key() on the client should be of the following
512 form::
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
524 Where the ticket blob is just appended to the above structure.
525
526
527 For the server, keys of type "rxrpc_s" must be made available to the server.
528 They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an
529 rxkad key for the AFS VL service). When such a key is created, it should be
530 given the server's secret key as the instantiation data (see the example
531 below).
532
533 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
534
535 A keyring is passed to the server socket by naming it in a sockopt. The server
536 socket then looks the server secret keys up in this keyring when secure
537 incoming connections are made. This can be seen in an example program that can
538 be found at:
539
540 http://people.redhat.com/~dhowells/rxrpc/listen.c
541
542
543 ====================
544 EXAMPLE CLIENT USAGE
545 ====================
546
547 A 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_ENCRYPT;
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 ================== ===================================
602 RXRPC_USER_CALL_ID specifies the user ID for this call
603 ================== ===================================
604
605 MSG_MORE should be set in msghdr::msg_flags on all but the last part of
606 the request. Multiple requests may be made simultaneously.
607
608 An RXRPC_TX_LENGTH control message can also be specified on the first
609 sendmsg() call.
610
611 If a call is intended to go to a destination other than the default
612 specified through connect(), then msghdr::msg_name should be set on the
613 first request message of that call.
614
615 (6) The reply data will then be posted to the server socket for recvmsg() to
616 pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data
617 for a particular call to be read. MSG_EOR will be set on the terminal
618 read for a call.
619
620 All data will be delivered with the following control message attached:
621
622 RXRPC_USER_CALL_ID - specifies the user ID for this call
623
624 If an abort or error occurred, this will be returned in the control data
625 buffer instead, and MSG_EOR will be flagged to indicate the end of that
626 call.
627
628 A client may ask for a service ID it knows and ask that this be upgraded to a
629 better service if one is available by supplying RXRPC_UPGRADE_SERVICE on the
630 first sendmsg() of a call. The client should then check srx_service in the
631 msg_name filled in by recvmsg() when collecting the result. srx_service will
632 hold the same value as given to sendmsg() if the upgrade request was ignored by
633 the service - otherwise it will be altered to indicate the service ID the
634 server upgraded to. Note that the upgraded service ID is chosen by the server.
635 The caller has to wait until it sees the service ID in the reply before sending
636 any more calls (further calls to the same destination will be blocked until the
637 probe is concluded).
638
639
640 Example Server Usage
641 ====================
642
643 A server would be set up to accept operations in the following manner:
644
645 (1) An RxRPC socket is created by::
646
647 server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET);
648
649 Where the third parameter indicates the address type of the transport
650 socket used - usually IPv4.
651
652 (2) Security is set up if desired by giving the socket a keyring with server
653 secret keys in it::
654
655 keyring = add_key("keyring", "AFSkeys", NULL, 0,
656 KEY_SPEC_PROCESS_KEYRING);
657
658 const char secret_key[8] = {
659 0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 };
660 add_key("rxrpc_s", "52:2", secret_key, 8, keyring);
661
662 setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7);
663
664 The keyring can be manipulated after it has been given to the socket. This
665 permits the server to add more keys, replace keys, etc. while it is live.
666
667 (3) A local address must then be bound::
668
669 struct sockaddr_rxrpc srx = {
670 .srx_family = AF_RXRPC,
671 .srx_service = VL_SERVICE_ID, /* RxRPC service ID */
672 .transport_type = SOCK_DGRAM, /* type of transport socket */
673 .transport.sin_family = AF_INET,
674 .transport.sin_port = htons(7000), /* AFS callback */
675 .transport.sin_address = 0, /* all local interfaces */
676 };
677 bind(server, &srx, sizeof(srx));
678
679 More than one service ID may be bound to a socket, provided the transport
680 parameters are the same. The limit is currently two. To do this, bind()
681 should be called twice.
682
683 (4) If service upgrading is required, first two service IDs must have been
684 bound and then the following option must be set::
685
686 unsigned short service_ids[2] = { from_ID, to_ID };
687 setsockopt(server, SOL_RXRPC, RXRPC_UPGRADEABLE_SERVICE,
688 service_ids, sizeof(service_ids));
689
690 This will automatically upgrade connections on service from_ID to service
691 to_ID if they request it. This will be reflected in msg_name obtained
692 through recvmsg() when the request data is delivered to userspace.
693
694 (5) The server is then set to listen out for incoming calls::
695
696 listen(server, 100);
697
698 (6) The kernel notifies the server of pending incoming connections by sending
699 it a message for each. This is received with recvmsg() on the server
700 socket. It has no data, and has a single dataless control message
701 attached::
702
703 RXRPC_NEW_CALL
704
705 The address that can be passed back by recvmsg() at this point should be
706 ignored since the call for which the message was posted may have gone by
707 the time it is accepted - in which case the first call still on the queue
708 will be accepted.
709
710 (7) The server then accepts the new call by issuing a sendmsg() with two
711 pieces of control data and no actual data:
712
713 ================== ==============================
714 RXRPC_ACCEPT indicate connection acceptance
715 RXRPC_USER_CALL_ID specify user ID for this call
716 ================== ==============================
717
718 (8) The first request data packet will then be posted to the server socket for
719 recvmsg() to pick up. At that point, the RxRPC address for the call can
720 be read from the address fields in the msghdr struct.
721
722 Subsequent request data will be posted to the server socket for recvmsg()
723 to collect as it arrives. All but the last piece of the request data will
724 be delivered with MSG_MORE flagged.
725
726 All data will be delivered with the following control message attached:
727
728
729 ================== ===================================
730 RXRPC_USER_CALL_ID specifies the user ID for this call
731 ================== ===================================
732
733 (9) The reply data should then be posted to the server socket using a series
734 of sendmsg() calls, each with the following control messages attached:
735
736 ================== ===================================
737 RXRPC_USER_CALL_ID specifies the user ID for this call
738 ================== ===================================
739
740 MSG_MORE should be set in msghdr::msg_flags on all but the last message
741 for a particular call.
742
743 (10) The final ACK from the client will be posted for retrieval by recvmsg()
744 when it is received. It will take the form of a dataless message with two
745 control messages attached:
746
747 ================== ===================================
748 RXRPC_USER_CALL_ID specifies the user ID for this call
749 RXRPC_ACK indicates final ACK (no data)
750 ================== ===================================
751
752 MSG_EOR will be flagged to indicate that this is the final message for
753 this call.
754
755 (11) Up to the point the final packet of reply data is sent, the call can be
756 aborted by calling sendmsg() with a dataless message with the following
757 control messages attached:
758
759 ================== ===================================
760 RXRPC_USER_CALL_ID specifies the user ID for this call
761 RXRPC_ABORT indicates abort code (4 byte data)
762 ================== ===================================
763
764 Any packets waiting in the socket's receive queue will be discarded if
765 this is issued.
766
767 Note that all the communications for a particular service take place through
768 the one server socket, using control messages on sendmsg() and recvmsg() to
769 determine the call affected.
770
771
772 AF_RXRPC Kernel Interface
773 =========================
774
775 The AF_RXRPC module also provides an interface for use by in-kernel utilities
776 such as the AFS filesystem. This permits such a utility to:
777
778 (1) Use different keys directly on individual client calls on one socket
779 rather than having to open a whole slew of sockets, one for each key it
780 might want to use.
781
782 (2) Avoid having RxRPC call request_key() at the point of issue of a call or
783 opening of a socket. Instead the utility is responsible for requesting a
784 key at the appropriate point. AFS, for instance, would do this during VFS
785 operations such as open() or unlink(). The key is then handed through
786 when the call is initiated.
787
788 (3) Request the use of something other than GFP_KERNEL to allocate memory.
789
790 (4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be
791 intercepted before they get put into the socket Rx queue and the socket
792 buffers manipulated directly.
793
794 To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,
795 bind an address as appropriate and listen if it's to be a server socket, but
796 then it passes this to the kernel interface functions.
797
798 The kernel interface functions are as follows:
799
800 (#) Begin a new client call::
801
802 struct rxrpc_call *
803 rxrpc_kernel_begin_call(struct socket *sock,
804 struct sockaddr_rxrpc *srx,
805 struct key *key,
806 unsigned long user_call_ID,
807 s64 tx_total_len,
808 gfp_t gfp,
809 rxrpc_notify_rx_t notify_rx,
810 bool upgrade,
811 bool intr,
812 unsigned int debug_id);
813
814 This allocates the infrastructure to make a new RxRPC call and assigns
815 call and connection numbers. The call will be made on the UDP port that
816 the socket is bound to. The call will go to the destination address of a
817 connected client socket unless an alternative is supplied (srx is
818 non-NULL).
819
820 If a key is supplied then this will be used to secure the call instead of
821 the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls
822 secured in this way will still share connections if at all possible.
823
824 The user_call_ID is equivalent to that supplied to sendmsg() in the
825 control data buffer. It is entirely feasible to use this to point to a
826 kernel data structure.
827
828 tx_total_len is the amount of data the caller is intending to transmit
829 with this call (or -1 if unknown at this point). Setting the data size
830 allows the kernel to encrypt directly to the packet buffers, thereby
831 saving a copy. The value may not be less than -1.
832
833 notify_rx is a pointer to a function to be called when events such as
834 incoming data packets or remote aborts happen.
835
836 upgrade should be set to true if a client operation should request that
837 the server upgrade the service to a better one. The resultant service ID
838 is returned by rxrpc_kernel_recv_data().
839
840 intr should be set to true if the call should be interruptible. If this
841 is not set, this function may not return until a channel has been
842 allocated; if it is set, the function may return -ERESTARTSYS.
843
844 debug_id is the call debugging ID to be used for tracing. This can be
845 obtained by atomically incrementing rxrpc_debug_id.
846
847 If this function is successful, an opaque reference to the RxRPC call is
848 returned. The caller now holds a reference on this and it must be
849 properly ended.
850
851 (#) Shut down a client call::
852
853 void rxrpc_kernel_shutdown_call(struct socket *sock,
854 struct rxrpc_call *call);
855
856 This is used to shut down a previously begun call. The user_call_ID is
857 expunged from AF_RXRPC's knowledge and will not be seen again in
858 association with the specified call.
859
860 (#) Release the ref on a client call::
861
862 void rxrpc_kernel_put_call(struct socket *sock,
863 struct rxrpc_call *call);
864
865 This is used to release the caller's ref on an rxrpc call.
866
867 (#) Send data through a call::
868
869 typedef void (*rxrpc_notify_end_tx_t)(struct sock *sk,
870 unsigned long user_call_ID,
871 struct sk_buff *skb);
872
873 int rxrpc_kernel_send_data(struct socket *sock,
874 struct rxrpc_call *call,
875 struct msghdr *msg,
876 size_t len,
877 rxrpc_notify_end_tx_t notify_end_rx);
878
879 This is used to supply either the request part of a client call or the
880 reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the
881 data buffers to be used. msg_iov may not be NULL and must point
882 exclusively to in-kernel virtual addresses. msg.msg_flags may be given
883 MSG_MORE if there will be subsequent data sends for this call.
884
885 The msg must not specify a destination address, control data or any flags
886 other than MSG_MORE. len is the total amount of data to transmit.
887
888 notify_end_rx can be NULL or it can be used to specify a function to be
889 called when the call changes state to end the Tx phase. This function is
890 called with a spinlock held to prevent the last DATA packet from being
891 transmitted until the function returns.
892
893 (#) Receive data from a call::
894
895 int rxrpc_kernel_recv_data(struct socket *sock,
896 struct rxrpc_call *call,
897 void *buf,
898 size_t size,
899 size_t *_offset,
900 bool want_more,
901 u32 *_abort,
902 u16 *_service)
903
904 This is used to receive data from either the reply part of a client call
905 or the request part of a service call. buf and size specify how much
906 data is desired and where to store it. *_offset is added on to buf and
907 subtracted from size internally; the amount copied into the buffer is
908 added to *_offset before returning.
909
910 want_more should be true if further data will be required after this is
911 satisfied and false if this is the last item of the receive phase.
912
913 There are three normal returns: 0 if the buffer was filled and want_more
914 was true; 1 if the buffer was filled, the last DATA packet has been
915 emptied and want_more was false; and -EAGAIN if the function needs to be
916 called again.
917
918 If the last DATA packet is processed but the buffer contains less than
919 the amount requested, EBADMSG is returned. If want_more wasn't set, but
920 more data was available, EMSGSIZE is returned.
921
922 If a remote ABORT is detected, the abort code received will be stored in
923 ``*_abort`` and ECONNABORTED will be returned.
924
925 The service ID that the call ended up with is returned into *_service.
926 This can be used to see if a call got a service upgrade.
927
928 (#) Abort a call??
929
930 ::
931
932 void rxrpc_kernel_abort_call(struct socket *sock,
933 struct rxrpc_call *call,
934 u32 abort_code);
935
936 This is used to abort a call if it's still in an abortable state. The
937 abort code specified will be placed in the ABORT message sent.
938
939 (#) Intercept received RxRPC messages::
940
941 typedef void (*rxrpc_interceptor_t)(struct sock *sk,
942 unsigned long user_call_ID,
943 struct sk_buff *skb);
944
945 void
946 rxrpc_kernel_intercept_rx_messages(struct socket *sock,
947 rxrpc_interceptor_t interceptor);
948
949 This installs an interceptor function on the specified AF_RXRPC socket.
950 All messages that would otherwise wind up in the socket's Rx queue are
951 then diverted to this function. Note that care must be taken to process
952 the messages in the right order to maintain DATA message sequentiality.
953
954 The interceptor function itself is provided with the address of the socket
955 and handling the incoming message, the ID assigned by the kernel utility
956 to the call and the socket buffer containing the message.
957
958 The skb->mark field indicates the type of message:
959
960 =============================== =======================================
961 Mark Meaning
962 =============================== =======================================
963 RXRPC_SKB_MARK_DATA Data message
964 RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call
965 RXRPC_SKB_MARK_BUSY Client call rejected as server busy
966 RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer
967 RXRPC_SKB_MARK_NET_ERROR Network error detected
968 RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered
969 RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance
970 =============================== =======================================
971
972 The remote abort message can be probed with rxrpc_kernel_get_abort_code().
973 The two error messages can be probed with rxrpc_kernel_get_error_number().
974 A new call can be accepted with rxrpc_kernel_accept_call().
975
976 Data messages can have their contents extracted with the usual bunch of
977 socket buffer manipulation functions. A data message can be determined to
978 be the last one in a sequence with rxrpc_kernel_is_data_last(). When a
979 data message has been used up, rxrpc_kernel_data_consumed() should be
980 called on it.
981
982 Messages should be handled to rxrpc_kernel_free_skb() to dispose of. It
983 is possible to get extra refs on all types of message for later freeing,
984 but this may pin the state of a call until the message is finally freed.
985
986 (#) Accept an incoming call::
987
988 struct rxrpc_call *
989 rxrpc_kernel_accept_call(struct socket *sock,
990 unsigned long user_call_ID);
991
992 This is used to accept an incoming call and to assign it a call ID. This
993 function is similar to rxrpc_kernel_begin_call() and calls accepted must
994 be ended in the same way.
995
996 If this function is successful, an opaque reference to the RxRPC call is
997 returned. The caller now holds a reference on this and it must be
998 properly ended.
999
1000 (#) Reject an incoming call::
1001
1002 int rxrpc_kernel_reject_call(struct socket *sock);
1003
1004 This is used to reject the first incoming call on the socket's queue with
1005 a BUSY message. -ENODATA is returned if there were no incoming calls.
1006 Other errors may be returned if the call had been aborted (-ECONNABORTED)
1007 or had timed out (-ETIME).
1008
1009 (#) Allocate a null key for doing anonymous security::
1010
1011 struct key *rxrpc_get_null_key(const char *keyname);
1012
1013 This is used to allocate a null RxRPC key that can be used to indicate
1014 anonymous security for a particular domain.
1015
1016 (#) Get the peer address of a call::
1017
1018 void rxrpc_kernel_get_peer(struct socket *sock, struct rxrpc_call *call,
1019 struct sockaddr_rxrpc *_srx);
1020
1021 This is used to find the remote peer address of a call.
1022
1023 (#) Set the total transmit data size on a call::
1024
1025 void rxrpc_kernel_set_tx_length(struct socket *sock,
1026 struct rxrpc_call *call,
1027 s64 tx_total_len);
1028
1029 This sets the amount of data that the caller is intending to transmit on a
1030 call. It's intended to be used for setting the reply size as the request
1031 size should be set when the call is begun. tx_total_len may not be less
1032 than zero.
1033
1034 (#) Get call RTT::
1035
1036 u64 rxrpc_kernel_get_rtt(struct socket *sock, struct rxrpc_call *call);
1037
1038 Get the RTT time to the peer in use by a call. The value returned is in
1039 nanoseconds.
1040
1041 (#) Check call still alive::
1042
1043 bool rxrpc_kernel_check_life(struct socket *sock,
1044 struct rxrpc_call *call,
1045 u32 *_life);
1046 void rxrpc_kernel_probe_life(struct socket *sock,
1047 struct rxrpc_call *call);
1048
1049 The first function passes back in ``*_life`` a number that is updated when
1050 ACKs are received from the peer (notably including PING RESPONSE ACKs
1051 which we can elicit by sending PING ACKs to see if the call still exists
1052 on the server). The caller should compare the numbers of two calls to see
1053 if the call is still alive after waiting for a suitable interval. It also
1054 returns true as long as the call hasn't yet reached the completed state.
1055
1056 This allows the caller to work out if the server is still contactable and
1057 if the call is still alive on the server while waiting for the server to
1058 process a client operation.
1059
1060 The second function causes a ping ACK to be transmitted to try to provoke
1061 the peer into responding, which would then cause the value returned by the
1062 first function to change. Note that this must be called in TASK_RUNNING
1063 state.
1064
1065 (#) Get remote client epoch::
1066
1067 u32 rxrpc_kernel_get_epoch(struct socket *sock,
1068 struct rxrpc_call *call)
1069
1070 This allows the epoch that's contained in packets of an incoming client
1071 call to be queried. This value is returned. The function always
1072 successful if the call is still in progress. It shouldn't be called once
1073 the call has expired. Note that calling this on a local client call only
1074 returns the local epoch.
1075
1076 This value can be used to determine if the remote client has been
1077 restarted as it shouldn't change otherwise.
1078
1079 (#) Set the maximum lifespan on a call::
1080
1081 void rxrpc_kernel_set_max_life(struct socket *sock,
1082 struct rxrpc_call *call,
1083 unsigned long hard_timeout)
1084
1085 This sets the maximum lifespan on a call to hard_timeout (which is in
1086 jiffies). In the event of the timeout occurring, the call will be
1087 aborted and -ETIME or -ETIMEDOUT will be returned.
1088
1089 (#) Apply the RXRPC_MIN_SECURITY_LEVEL sockopt to a socket from within in the
1090 kernel::
1091
1092 int rxrpc_sock_set_min_security_level(struct sock *sk,
1093 unsigned int val);
1094
1095 This specifies the minimum security level required for calls on this
1096 socket.
1097
1098
1099 Configurable Parameters
1100 =======================
1101
1102 The RxRPC protocol driver has a number of configurable parameters that can be
1103 adjusted through sysctls in /proc/net/rxrpc/:
1104
1105 (#) req_ack_delay
1106
1107 The amount of time in milliseconds after receiving a packet with the
1108 request-ack flag set before we honour the flag and actually send the
1109 requested ack.
1110
1111 Usually the other side won't stop sending packets until the advertised
1112 reception window is full (to a maximum of 255 packets), so delaying the
1113 ACK permits several packets to be ACK'd in one go.
1114
1115 (#) soft_ack_delay
1116
1117 The amount of time in milliseconds after receiving a new packet before we
1118 generate a soft-ACK to tell the sender that it doesn't need to resend.
1119
1120 (#) idle_ack_delay
1121
1122 The amount of time in milliseconds after all the packets currently in the
1123 received queue have been consumed before we generate a hard-ACK to tell
1124 the sender it can free its buffers, assuming no other reason occurs that
1125 we would send an ACK.
1126
1127 (#) resend_timeout
1128
1129 The amount of time in milliseconds after transmitting a packet before we
1130 transmit it again, assuming no ACK is received from the receiver telling
1131 us they got it.
1132
1133 (#) max_call_lifetime
1134
1135 The maximum amount of time in seconds that a call may be in progress
1136 before we preemptively kill it.
1137
1138 (#) dead_call_expiry
1139
1140 The amount of time in seconds before we remove a dead call from the call
1141 list. Dead calls are kept around for a little while for the purpose of
1142 repeating ACK and ABORT packets.
1143
1144 (#) connection_expiry
1145
1146 The amount of time in seconds after a connection was last used before we
1147 remove it from the connection list. While a connection is in existence,
1148 it serves as a placeholder for negotiated security; when it is deleted,
1149 the security must be renegotiated.
1150
1151 (#) transport_expiry
1152
1153 The amount of time in seconds after a transport was last used before we
1154 remove it from the transport list. While a transport is in existence, it
1155 serves to anchor the peer data and keeps the connection ID counter.
1156
1157 (#) rxrpc_rx_window_size
1158
1159 The size of the receive window in packets. This is the maximum number of
1160 unconsumed received packets we're willing to hold in memory for any
1161 particular call.
1162
1163 (#) rxrpc_rx_mtu
1164
1165 The maximum packet MTU size that we're willing to receive in bytes. This
1166 indicates to the peer whether we're willing to accept jumbo packets.
1167
1168 (#) rxrpc_rx_jumbo_max
1169
1170 The maximum number of packets that we're willing to accept in a jumbo
1171 packet. Non-terminal packets in a jumbo packet must contain a four byte
1172 header plus exactly 1412 bytes of data. The terminal packet must contain
1173 a four byte header plus any amount of data. In any event, a jumbo packet
1174 may not exceed rxrpc_rx_mtu in size.
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