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1.. SPDX-License-Identifier: GPL-2.02 3======================4RxRPC Network Protocol5======================6 7The RxRPC protocol driver provides a reliable two-phase transport on top of UDP8that can be used to perform RxRPC remote operations. This is done over sockets9of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and10receive data, aborts and errors.11 12Contents 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 35Overview36========37 38RxRPC is a two-layer protocol. There is a session layer which provides39reliable virtual connections using UDP over IPv4 (or IPv6) as the transport40layer, but implements a real network protocol; and there's the presentation41layer which renders structured data to binary blobs and back again using XDR42(as does SunRPC)::43 44 +-------------+45 | Application |46 +-------------+47 | XDR | Presentation48 +-------------+49 | RxRPC | Session50 +-------------+51 | UDP | Transport52 +-------------+53 54 55AF_RXRPC provides:56 57 (1) Part of an RxRPC facility for both kernel and userspace applications by58 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 then61 receives a blob (the reply), and the server receives the request and then62 transmits the reply.63 64 (3) Retention of the reusable bits of the transport system set up for one call65 to speed up subsequent calls.66 67 (4) A secure protocol, using the Linux kernel's key retention facility to68 manage security on the client end. The server end must of necessity be69 more active in security negotiations.70 71AF_RXRPC does not provide XDR marshalling/presentation facilities. That is72left to the application. AF_RXRPC only deals in blobs. Even the operation ID73is just the first four bytes of the request blob, and as such is beyond the74kernel's interest.75 76 77Sockets 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 going82 to use - currently only PF_INET is supported.83 84 85The Andrew File System (AFS) is an example of an application that uses this and86that has both kernel (filesystem) and userspace (utility) components.87 88 89RxRPC Protocol Summary90======================91 92An overview of the RxRPC protocol:93 94 (#) RxRPC sits on top of another networking protocol (UDP is the only option95 currently), and uses this to provide network transport. UDP ports, for96 example, provide transport endpoints.97 98 (#) RxRPC supports multiple virtual "connections" from any given transport99 endpoint, thus allowing the endpoints to be shared, even to the same100 remote endpoint.101 102 (#) Each connection goes to a particular "service". A connection may not go103 to multiple services. A service may be considered the RxRPC equivalent of104 a port number. AF_RXRPC permits multiple services to share an endpoint.105 106 (#) Client-originating packets are marked, thus a transport endpoint can be107 shared between client and server connections (connections have a108 direction).109 110 (#) Up to a billion connections may be supported concurrently between one111 local transport endpoint and one service on one remote endpoint. An RxRPC112 connection is described by seven numbers::113 114 Local address }115 Local port } Transport (UDP) address116 Remote address }117 Remote port }118 Direction119 Connection ID120 Service ID121 122 (#) Each RxRPC operation is a "call". A connection may make up to four123 billion calls, but only up to four calls may be in progress on a124 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 data128 which the client receives.129 130 (#) The data blobs are of indefinite size, the end of a phase is marked with a131 flag in the packet. The number of packets of data making up one blob may132 not exceed 4 billion, however, as this would cause the sequence number to133 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 is138 initiated by the first data packet on it arriving. If security is139 requested, the server then issues a "challenge" and then the client140 replies with a "response". If the response is successful, the security is141 set for the lifetime of that connection, and all subsequent calls made142 upon it use that same security. In the event that the server lets a143 connection lapse before the client, the security will be renegotiated if144 the client uses the connection again.145 146 (#) Calls use ACK packets to handle reliability. Data packets are also147 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 point151 has been received and processed; a soft-ACK indicates that the data has152 been received but may yet be discarded and re-requested. The sender may153 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 data156 packets that make up the request.157 158 (#) An call is complete when the request has been sent, the reply has been159 received and the final hard-ACK on the last packet of the reply has160 reached the server.161 162 (#) An call may be aborted by either end at any time up to its completion.163 164 165AF_RXRPC Driver Model166=====================167 168About the AF_RXRPC driver:169 170 (#) The AF_RXRPC protocol transparently uses internal sockets of the transport171 protocol to represent transport endpoints.172 173 (#) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC174 connections are handled transparently. One client socket may be used to175 make multiple simultaneous calls to the same service. One server socket176 may handle calls from many clients.177 178 (#) Additional parallel client connections will be initiated to support extra179 concurrent calls, up to a tunable limit.180 181 (#) Each connection is retained for a certain amount of time [tunable] after182 the last call currently using it has completed in case a new call is made183 that could reuse it.184 185 (#) Each internal UDP socket is retained [tunable] for a certain amount of186 time [tunable] after the last connection using it discarded, in case a new187 connection is made that could use it.188 189 (#) A client-side connection is only shared between calls if they have190 the same key struct describing their security (and assuming the calls191 would otherwise share the connection). Non-secured calls would also be192 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 ping197 replying.198 199 (#) SO_KEEPALIVE automatically pings the other side to keep the connection200 alive [TODO].201 202 (#) If an ICMP error is received, all calls affected by that error will be203 aborted with an appropriate network error passed through recvmsg().204 205 206Interaction with the user of the RxRPC socket:207 208 (#) A socket is made into a server socket by binding an address with a209 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 to215 be used in all other sendmsgs or recvmsgs associated with that call. The216 tag is carried in the control data.217 218 (#) connect() is used to supply a default destination address for a client219 socket. This may be overridden by supplying an alternate address to the220 first sendmsg() of a call (struct msghdr::msg_name).221 222 (#) If connect() is called on an unbound client, a random local port will223 bound before the operation takes place.224 225 (#) A server socket may also be used to make client calls. To do this, the226 first sendmsg() of the call must specify the target address. The server's227 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 pin231 client resources. A new call can then be initiated with the same tag232 without fear of interference.233 234 (#) In the server, a request is received with one or more recvmsgs, then the235 the reply is transmitted with one or more sendmsgs, and then the final ACK236 is received with a last recvmsg.237 238 (#) When sending data for a call, sendmsg is given MSG_MORE if there's more239 data to come on that call.240 241 (#) When receiving data for a call, recvmsg flags MSG_MORE if there's more242 data to come for that call.243 244 (#) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg245 to indicate the terminal message for that call.246 247 (#) A call may be aborted by adding an abort control message to the control248 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. Receiving253 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 a266 message to server application to let it know there's a new call awaiting267 its acceptance [recvmsg reports a special control message]. The server268 application then uses sendmsg to assign a tag to the new call. Once that269 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 of272 secret keys corresponding to the security types it permits. When a secure273 connection is being set up, the kernel looks up the appropriate secret key274 in the keyring and then sends a challenge packet to the client and275 receives a response packet. The kernel then checks the authorisation of276 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 is279 nominated by a socket option.280 281 282Notes on sendmsg:283 284 (#) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is285 making progress at accepting packets within a reasonable time such that we286 manage to queue up all the data for transmission. This requires the287 client to accept at least one packet per 2*RTT time period.288 289 If this isn't set, sendmsg() will return immediately, either returning290 EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data291 consumed.292 293 294Notes on recvmsg:295 296 (#) If there's a sequence of data messages belonging to a particular call on297 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, or304 305 (d) it fills the user buffer.306 307 If recvmsg is called in blocking mode, it will keep sleeping, awaiting the308 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 any311 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 queue315 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 byte318 of the last data message in that phase yet), then MSG_MORE will be319 flagged.320 321 322Control Messages323================324 325AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex326calls, to invoke certain actions and to report certain conditions. These are:327 328 ======================= === =========== ===============================329 MESSAGE ID SRT DATA MEANING330 ======================= === =========== ===============================331 RXRPC_USER_CALL_ID sr- User ID App's call specifier332 RXRPC_ABORT srt Abort code Abort code to issue/received333 RXRPC_ACK -rt n/a Final ACK received334 RXRPC_NET_ERROR -rt error num Network error on call335 RXRPC_BUSY -rt n/a Call rejected (server busy)336 RXRPC_LOCAL_ERROR -rt error num Local error encountered337 RXRPC_NEW_CALL -r- n/a New call received338 RXRPC_ACCEPT s-- n/a Accept new call339 RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call340 RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded341 RXRPC_TX_LENGTH s-- data len Total length of Tx data342 ======================= === =========== ===============================343 344 (SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)345 346 (#) RXRPC_USER_CALL_ID347 348 This is used to indicate the application's call ID. It's an unsigned long349 that the app specifies in the client by attaching it to the first data350 message or in the server by passing it in association with an RXRPC_ACCEPT351 message. recvmsg() passes it in conjunction with all messages except352 those of the RXRPC_NEW_CALL message.353 354 (#) RXRPC_ABORT355 356 This is can be used by an application to abort a call by passing it to357 sendmsg, or it can be delivered by recvmsg to indicate a remote abort was358 received. Either way, it must be associated with an RXRPC_USER_CALL_ID to359 specify the call affected. If an abort is being sent, then error EBADSLT360 will be returned if there is no call with that user ID.361 362 (#) RXRPC_ACK363 364 This is delivered to a server application to indicate that the final ACK365 of a call was received from the client. It will be associated with an366 RXRPC_USER_CALL_ID to indicate the call that's now complete.367 368 (#) RXRPC_NET_ERROR369 370 This is delivered to an application to indicate that an ICMP error message371 was encountered in the process of trying to talk to the peer. An372 errno-class integer value will be included in the control message data373 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call374 affected.375 376 (#) RXRPC_BUSY377 378 This is delivered to a client application to indicate that a call was379 rejected by the server due to the server being busy. It will be380 associated with an RXRPC_USER_CALL_ID to indicate the rejected call.381 382 (#) RXRPC_LOCAL_ERROR383 384 This is delivered to an application to indicate that a local error was385 encountered and that a call has been aborted because of it. An386 errno-class integer value will be included in the control message data387 indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call388 affected.389 390 (#) RXRPC_NEW_CALL391 392 This is delivered to indicate to a server application that a new call has393 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_ACCEPT397 398 This is used by a server application to attempt to accept a call and399 assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID400 to indicate the user ID to be assigned. If there is no call to be401 accepted (it may have timed out, been aborted, etc.), then sendmsg will402 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_CALL406 407 This is used to indicate that a client call should be made on a one-off408 connection. The connection is discarded once the call has terminated.409 410 (#) RXRPC_UPGRADE_SERVICE411 412 This is used to make a client call to probe if the specified service ID413 may be upgraded by the server. The caller must check msg_name returned to414 recvmsg() for the service ID actually in use. The operation probed must415 be one that takes the same arguments in both services.416 417 Once this has been used to establish the upgrade capability (or lack418 thereof) of the server, the service ID returned should be used for all419 future communication to that server and RXRPC_UPGRADE_SERVICE should no420 longer be set.421 422 (#) RXRPC_TX_LENGTH423 424 This is used to inform the kernel of the total amount of data that is425 going to be transmitted by a call (whether in a client request or a426 service response). If given, it allows the kernel to encrypt from the427 userspace buffer directly to the packet buffers, rather than copying into428 the buffer and then encrypting in place. This may only be given with the429 first sendmsg() providing data for a call. EMSGSIZE will be generated if430 the amount of data actually given is different.431 432 This takes a parameter of __s64 type that indicates how much will be433 transmitted. This may not be less than zero.434 435The symbol RXRPC__SUPPORTED is defined as one more than the highest control436message type supported. At run time this can be queried by means of the437RXRPC_SUPPORTED_CMSG socket option (see below).438 439 440==============441SOCKET OPTIONS442==============443 444AF_RXRPC sockets support a few socket options at the SOL_RXRPC level:445 446 (#) RXRPC_SECURITY_KEY447 448 This is used to specify the description of the key to be used. The key is449 extracted from the calling process's keyrings with request_key() and450 should be of "rxrpc" type.451 452 The optval pointer points to the description string, and optlen indicates453 how long the string is, without the NUL terminator.454 455 (#) RXRPC_SECURITY_KEYRING456 457 Similar to above but specifies a keyring of server secret keys to use (key458 type "keyring"). See the "Security" section.459 460 (#) RXRPC_EXCLUSIVE_CONNECTION461 462 This is used to request that new connections should be used for each call463 made subsequently on this socket. optval should be NULL and optlen 0.464 465 (#) RXRPC_MIN_SECURITY_LEVEL466 467 This is used to specify the minimum security level required for calls on468 this socket. optval must point to an int containing one of the following469 values:470 471 (a) RXRPC_SECURITY_PLAIN472 473 Encrypted checksum only.474 475 (b) RXRPC_SECURITY_AUTH476 477 Encrypted checksum plus packet padded and first eight bytes of packet478 encrypted - which includes the actual packet length.479 480 (c) RXRPC_SECURITY_ENCRYPT481 482 Encrypted checksum plus entire packet padded and encrypted, including483 actual packet length.484 485 (#) RXRPC_UPGRADEABLE_SERVICE486 487 This is used to indicate that a service socket with two bindings may488 upgrade one bound service to the other if requested by the client. optval489 must point to an array of two unsigned short ints. The first is the490 service ID to upgrade from and the second the service ID to upgrade to.491 492 (#) RXRPC_SUPPORTED_CMSG493 494 This is a read-only option that writes an int into the buffer indicating495 the highest control message type supported.496 497 498========499SECURITY500========501 502Currently, only the kerberos 4 equivalent protocol has been implemented503(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 AFS505kaserver or the kerberos server and installed as "rxrpc" type keys. This is506normally done using the klog program. An example simple klog program can be507found at:508 509 http://people.redhat.com/~dhowells/rxrpc/klog.c510 511The payload provided to add_key() on the client should be of the following512form::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 an529rxkad key for the AFS VL service). When such a key is created, it should be530given the server's secret key as the instantiation data (see the example531below).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 server536socket then looks the server secret keys up in this keyring when secure537incoming connections are made. This can be seen in an example program that can538be found at:539 540 http://people.redhat.com/~dhowells/rxrpc/listen.c541 542 543====================544EXAMPLE CLIENT USAGE545====================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 transport554 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 random569 non-privileged port will be used. A UDP port may be shared between570 several unrelated RxRPC sockets. Security is handled on a basis of571 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 security579 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 can586 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 series599 of sendmsg() calls, each with the following control message attached:600 601 ================== ===================================602 RXRPC_USER_CALL_ID specifies the user ID for this call603 ================== ===================================604 605 MSG_MORE should be set in msghdr::msg_flags on all but the last part of606 the request. Multiple requests may be made simultaneously.607 608 An RXRPC_TX_LENGTH control message can also be specified on the first609 sendmsg() call.610 611 If a call is intended to go to a destination other than the default612 specified through connect(), then msghdr::msg_name should be set on the613 first request message of that call.614 615 (6) The reply data will then be posted to the server socket for recvmsg() to616 pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data617 for a particular call to be read. MSG_EOR will be set on the terminal618 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 call623 624 If an abort or error occurred, this will be returned in the control data625 buffer instead, and MSG_EOR will be flagged to indicate the end of that626 call.627 628A client may ask for a service ID it knows and ask that this be upgraded to a629better service if one is available by supplying RXRPC_UPGRADE_SERVICE on the630first sendmsg() of a call. The client should then check srx_service in the631msg_name filled in by recvmsg() when collecting the result. srx_service will632hold the same value as given to sendmsg() if the upgrade request was ignored by633the service - otherwise it will be altered to indicate the service ID the634server upgraded to. Note that the upgraded service ID is chosen by the server.635The caller has to wait until it sees the service ID in the reply before sending636any more calls (further calls to the same destination will be blocked until the637probe is concluded).638 639 640Example Server Usage641====================642 643A 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 transport650 socket used - usually IPv4.651 652 (2) Security is set up if desired by giving the socket a keyring with server653 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. This665 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 transport680 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 been684 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 service691 to_ID if they request it. This will be reflected in msg_name obtained692 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 sending699 it a message for each. This is received with recvmsg() on the server700 socket. It has no data, and has a single dataless control message701 attached::702 703 RXRPC_NEW_CALL704 705 The address that can be passed back by recvmsg() at this point should be706 ignored since the call for which the message was posted may have gone by707 the time it is accepted - in which case the first call still on the queue708 will be accepted.709 710 (7) The server then accepts the new call by issuing a sendmsg() with two711 pieces of control data and no actual data:712 713 ================== ==============================714 RXRPC_ACCEPT indicate connection acceptance715 RXRPC_USER_CALL_ID specify user ID for this call716 ================== ==============================717 718 (8) The first request data packet will then be posted to the server socket for719 recvmsg() to pick up. At that point, the RxRPC address for the call can720 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 will724 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 call731 ================== ===================================732 733 (9) The reply data should then be posted to the server socket using a series734 of sendmsg() calls, each with the following control messages attached:735 736 ================== ===================================737 RXRPC_USER_CALL_ID specifies the user ID for this call738 ================== ===================================739 740 MSG_MORE should be set in msghdr::msg_flags on all but the last message741 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 two745 control messages attached:746 747 ================== ===================================748 RXRPC_USER_CALL_ID specifies the user ID for this call749 RXRPC_ACK indicates final ACK (no data)750 ================== ===================================751 752 MSG_EOR will be flagged to indicate that this is the final message for753 this call.754 755(11) Up to the point the final packet of reply data is sent, the call can be756 aborted by calling sendmsg() with a dataless message with the following757 control messages attached:758 759 ================== ===================================760 RXRPC_USER_CALL_ID specifies the user ID for this call761 RXRPC_ABORT indicates abort code (4 byte data)762 ================== ===================================763 764 Any packets waiting in the socket's receive queue will be discarded if765 this is issued.766 767Note that all the communications for a particular service take place through768the one server socket, using control messages on sendmsg() and recvmsg() to769determine the call affected.770 771 772AF_RXRPC Kernel Interface773=========================774 775The AF_RXRPC module also provides an interface for use by in-kernel utilities776such as the AFS filesystem. This permits such a utility to:777 778 (1) Use different keys directly on individual client calls on one socket779 rather than having to open a whole slew of sockets, one for each key it780 might want to use.781 782 (2) Avoid having RxRPC call request_key() at the point of issue of a call or783 opening of a socket. Instead the utility is responsible for requesting a784 key at the appropriate point. AFS, for instance, would do this during VFS785 operations such as open() or unlink(). The key is then handed through786 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 be791 intercepted before they get put into the socket Rx queue and the socket792 buffers manipulated directly.793 794To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket,795bind an address as appropriate and listen if it's to be a server socket, but796then it passes this to the kernel interface functions.797 798The 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 assigns815 call and connection numbers. The call will be made on the UDP port that816 the socket is bound to. The call will go to the destination address of a817 connected client socket unless an alternative is supplied (srx is818 non-NULL).819 820 If a key is supplied then this will be used to secure the call instead of821 the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls822 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 the825 control data buffer. It is entirely feasible to use this to point to a826 kernel data structure.827 828 tx_total_len is the amount of data the caller is intending to transmit829 with this call (or -1 if unknown at this point). Setting the data size830 allows the kernel to encrypt directly to the packet buffers, thereby831 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 as834 incoming data packets or remote aborts happen.835 836 upgrade should be set to true if a client operation should request that837 the server upgrade the service to a better one. The resultant service ID838 is returned by rxrpc_kernel_recv_data().839 840 intr should be set to true if the call should be interruptible. If this841 is not set, this function may not return until a channel has been842 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 be845 obtained by atomically incrementing rxrpc_debug_id.846 847 If this function is successful, an opaque reference to the RxRPC call is848 returned. The caller now holds a reference on this and it must be849 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 is857 expunged from AF_RXRPC's knowledge and will not be seen again in858 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 the880 reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the881 data buffers to be used. msg_iov may not be NULL and must point882 exclusively to in-kernel virtual addresses. msg.msg_flags may be given883 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 flags886 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 be889 called when the call changes state to end the Tx phase. This function is890 called with a spinlock held to prevent the last DATA packet from being891 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 call905 or the request part of a service call. buf and size specify how much906 data is desired and where to store it. *_offset is added on to buf and907 subtracted from size internally; the amount copied into the buffer is908 added to *_offset before returning.909 910 want_more should be true if further data will be required after this is911 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_more914 was true; 1 if the buffer was filled, the last DATA packet has been915 emptied and want_more was false; and -EAGAIN if the function needs to be916 called again.917 918 If the last DATA packet is processed but the buffer contains less than919 the amount requested, EBADMSG is returned. If want_more wasn't set, but920 more data was available, EMSGSIZE is returned.921 922 If a remote ABORT is detected, the abort code received will be stored in923 ``*_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. The937 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 void946 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 are951 then diverted to this function. Note that care must be taken to process952 the messages in the right order to maintain DATA message sequentiality.953 954 The interceptor function itself is provided with the address of the socket955 and handling the incoming message, the ID assigned by the kernel utility956 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 Meaning962 =============================== =======================================963 RXRPC_SKB_MARK_DATA Data message964 RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call965 RXRPC_SKB_MARK_BUSY Client call rejected as server busy966 RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer967 RXRPC_SKB_MARK_NET_ERROR Network error detected968 RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered969 RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance970 =============================== =======================================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 of977 socket buffer manipulation functions. A data message can be determined to978 be the last one in a sequence with rxrpc_kernel_is_data_last(). When a979 data message has been used up, rxrpc_kernel_data_consumed() should be980 called on it.981 982 Messages should be handled to rxrpc_kernel_free_skb() to dispose of. It983 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. This993 function is similar to rxrpc_kernel_begin_call() and calls accepted must994 be ended in the same way.995 996 If this function is successful, an opaque reference to the RxRPC call is997 returned. The caller now holds a reference on this and it must be998 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 with1005 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 indicate1014 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 a1030 call. It's intended to be used for setting the reply size as the request1031 size should be set when the call is begun. tx_total_len may not be less1032 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 in1039 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 when1050 ACKs are received from the peer (notably including PING RESPONSE ACKs1051 which we can elicit by sending PING ACKs to see if the call still exists1052 on the server). The caller should compare the numbers of two calls to see1053 if the call is still alive after waiting for a suitable interval. It also1054 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 and1057 if the call is still alive on the server while waiting for the server to1058 process a client operation.1059 1060 The second function causes a ping ACK to be transmitted to try to provoke1061 the peer into responding, which would then cause the value returned by the1062 first function to change. Note that this must be called in TASK_RUNNING1063 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 client1071 call to be queried. This value is returned. The function always1072 successful if the call is still in progress. It shouldn't be called once1073 the call has expired. Note that calling this on a local client call only1074 returns the local epoch.1075 1076 This value can be used to determine if the remote client has been1077 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 in1086 jiffies). In the event of the timeout occurring, the call will be1087 aborted and -ETIME or -ETIMEDOUT will be returned.1088 1089 (#) Apply the RXRPC_MIN_SECURITY_LEVEL sockopt to a socket from within in the1090 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 this1096 socket.1097 1098 1099Configurable Parameters1100=======================1101 1102The RxRPC protocol driver has a number of configurable parameters that can be1103adjusted through sysctls in /proc/net/rxrpc/:1104 1105 (#) req_ack_delay1106 1107 The amount of time in milliseconds after receiving a packet with the1108 request-ack flag set before we honour the flag and actually send the1109 requested ack.1110 1111 Usually the other side won't stop sending packets until the advertised1112 reception window is full (to a maximum of 255 packets), so delaying the1113 ACK permits several packets to be ACK'd in one go.1114 1115 (#) soft_ack_delay1116 1117 The amount of time in milliseconds after receiving a new packet before we1118 generate a soft-ACK to tell the sender that it doesn't need to resend.1119 1120 (#) idle_ack_delay1121 1122 The amount of time in milliseconds after all the packets currently in the1123 received queue have been consumed before we generate a hard-ACK to tell1124 the sender it can free its buffers, assuming no other reason occurs that1125 we would send an ACK.1126 1127 (#) resend_timeout1128 1129 The amount of time in milliseconds after transmitting a packet before we1130 transmit it again, assuming no ACK is received from the receiver telling1131 us they got it.1132 1133 (#) max_call_lifetime1134 1135 The maximum amount of time in seconds that a call may be in progress1136 before we preemptively kill it.1137 1138 (#) dead_call_expiry1139 1140 The amount of time in seconds before we remove a dead call from the call1141 list. Dead calls are kept around for a little while for the purpose of1142 repeating ACK and ABORT packets.1143 1144 (#) connection_expiry1145 1146 The amount of time in seconds after a connection was last used before we1147 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_expiry1152 1153 The amount of time in seconds after a transport was last used before we1154 remove it from the transport list. While a transport is in existence, it1155 serves to anchor the peer data and keeps the connection ID counter.1156 1157 (#) rxrpc_rx_window_size1158 1159 The size of the receive window in packets. This is the maximum number of1160 unconsumed received packets we're willing to hold in memory for any1161 particular call.1162 1163 (#) rxrpc_rx_mtu1164 1165 The maximum packet MTU size that we're willing to receive in bytes. This1166 indicates to the peer whether we're willing to accept jumbo packets.1167 1168 (#) rxrpc_rx_jumbo_max1169 1170 The maximum number of packets that we're willing to accept in a jumbo1171 packet. Non-terminal packets in a jumbo packet must contain a four byte1172 header plus exactly 1412 bytes of data. The terminal packet must contain1173 a four byte header plus any amount of data. In any event, a jumbo packet1174 may not exceed rxrpc_rx_mtu in size.1175