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diff --git a/Documentation/networking/rxrpc.rst b/Documentation/networking/rxrpc.rst new file mode 100644 index 000000000000..68552b92dc44 --- /dev/null +++ b/Documentation/networking/rxrpc.rst @@ -0,0 +1,1178 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================== +RxRPC Network Protocol +====================== + +The RxRPC protocol driver provides a reliable two-phase transport on top of UDP +that can be used to perform RxRPC remote operations. This is done over sockets +of AF_RXRPC family, using sendmsg() and recvmsg() with control data to send and +receive data, aborts and errors. + +Contents of this document: + + (#) Overview. + + (#) RxRPC protocol summary. + + (#) AF_RXRPC driver model. + + (#) Control messages. + + (#) Socket options. + + (#) Security. + + (#) Example client usage. + + (#) Example server usage. + + (#) AF_RXRPC kernel interface. + + (#) Configurable parameters. + + +Overview +======== + +RxRPC is a two-layer protocol. There is a session layer which provides +reliable virtual connections using UDP over IPv4 (or IPv6) as the transport +layer, but implements a real network protocol; and there's the presentation +layer which renders structured data to binary blobs and back again using XDR +(as does SunRPC):: + + +-------------+ + | Application | + +-------------+ + | XDR | Presentation + +-------------+ + | RxRPC | Session + +-------------+ + | UDP | Transport + +-------------+ + + +AF_RXRPC provides: + + (1) Part of an RxRPC facility for both kernel and userspace applications by + making the session part of it a Linux network protocol (AF_RXRPC). + + (2) A two-phase protocol. The client transmits a blob (the request) and then + receives a blob (the reply), and the server receives the request and then + transmits the reply. + + (3) Retention of the reusable bits of the transport system set up for one call + to speed up subsequent calls. + + (4) A secure protocol, using the Linux kernel's key retention facility to + manage security on the client end. The server end must of necessity be + more active in security negotiations. + +AF_RXRPC does not provide XDR marshalling/presentation facilities. That is +left to the application. AF_RXRPC only deals in blobs. Even the operation ID +is just the first four bytes of the request blob, and as such is beyond the +kernel's interest. + + +Sockets of AF_RXRPC family are: + + (1) created as type SOCK_DGRAM; + + (2) provided with a protocol of the type of underlying transport they're going + to use - currently only PF_INET is supported. + + +The Andrew File System (AFS) is an example of an application that uses this and +that has both kernel (filesystem) and userspace (utility) components. + + +RxRPC Protocol Summary +====================== + +An overview of the RxRPC protocol: + + (#) RxRPC sits on top of another networking protocol (UDP is the only option + currently), and uses this to provide network transport. UDP ports, for + example, provide transport endpoints. + + (#) RxRPC supports multiple virtual "connections" from any given transport + endpoint, thus allowing the endpoints to be shared, even to the same + remote endpoint. + + (#) Each connection goes to a particular "service". A connection may not go + to multiple services. A service may be considered the RxRPC equivalent of + a port number. AF_RXRPC permits multiple services to share an endpoint. + + (#) Client-originating packets are marked, thus a transport endpoint can be + shared between client and server connections (connections have a + direction). + + (#) Up to a billion connections may be supported concurrently between one + local transport endpoint and one service on one remote endpoint. An RxRPC + connection is described by seven numbers:: + + Local address } + Local port } Transport (UDP) address + Remote address } + Remote port } + Direction + Connection ID + Service ID + + (#) Each RxRPC operation is a "call". A connection may make up to four + billion calls, but only up to four calls may be in progress on a + connection at any one time. + + (#) Calls are two-phase and asymmetric: the client sends its request data, + which the service receives; then the service transmits the reply data + which the client receives. + + (#) The data blobs are of indefinite size, the end of a phase is marked with a + flag in the packet. The number of packets of data making up one blob may + not exceed 4 billion, however, as this would cause the sequence number to + wrap. + + (#) The first four bytes of the request data are the service operation ID. + + (#) Security is negotiated on a per-connection basis. The connection is + initiated by the first data packet on it arriving. If security is + requested, the server then issues a "challenge" and then the client + replies with a "response". If the response is successful, the security is + set for the lifetime of that connection, and all subsequent calls made + upon it use that same security. In the event that the server lets a + connection lapse before the client, the security will be renegotiated if + the client uses the connection again. + + (#) Calls use ACK packets to handle reliability. Data packets are also + explicitly sequenced per call. + + (#) There are two types of positive acknowledgment: hard-ACKs and soft-ACKs. + A hard-ACK indicates to the far side that all the data received to a point + has been received and processed; a soft-ACK indicates that the data has + been received but may yet be discarded and re-requested. The sender may + not discard any transmittable packets until they've been hard-ACK'd. + + (#) Reception of a reply data packet implicitly hard-ACK's all the data + packets that make up the request. + + (#) An call is complete when the request has been sent, the reply has been + received and the final hard-ACK on the last packet of the reply has + reached the server. + + (#) An call may be aborted by either end at any time up to its completion. + + +AF_RXRPC Driver Model +===================== + +About the AF_RXRPC driver: + + (#) The AF_RXRPC protocol transparently uses internal sockets of the transport + protocol to represent transport endpoints. + + (#) AF_RXRPC sockets map onto RxRPC connection bundles. Actual RxRPC + connections are handled transparently. One client socket may be used to + make multiple simultaneous calls to the same service. One server socket + may handle calls from many clients. + + (#) Additional parallel client connections will be initiated to support extra + concurrent calls, up to a tunable limit. + + (#) Each connection is retained for a certain amount of time [tunable] after + the last call currently using it has completed in case a new call is made + that could reuse it. + + (#) Each internal UDP socket is retained [tunable] for a certain amount of + time [tunable] after the last connection using it discarded, in case a new + connection is made that could use it. + + (#) A client-side connection is only shared between calls if they have have + the same key struct describing their security (and assuming the calls + would otherwise share the connection). Non-secured calls would also be + able to share connections with each other. + + (#) A server-side connection is shared if the client says it is. + + (#) ACK'ing is handled by the protocol driver automatically, including ping + replying. + + (#) SO_KEEPALIVE automatically pings the other side to keep the connection + alive [TODO]. + + (#) If an ICMP error is received, all calls affected by that error will be + aborted with an appropriate network error passed through recvmsg(). + + +Interaction with the user of the RxRPC socket: + + (#) A socket is made into a server socket by binding an address with a + non-zero service ID. + + (#) In the client, sending a request is achieved with one or more sendmsgs, + followed by the reply being received with one or more recvmsgs. + + (#) The first sendmsg for a request to be sent from a client contains a tag to + be used in all other sendmsgs or recvmsgs associated with that call. The + tag is carried in the control data. + + (#) connect() is used to supply a default destination address for a client + socket. This may be overridden by supplying an alternate address to the + first sendmsg() of a call (struct msghdr::msg_name). + + (#) If connect() is called on an unbound client, a random local port will + bound before the operation takes place. + + (#) A server socket may also be used to make client calls. To do this, the + first sendmsg() of the call must specify the target address. The server's + transport endpoint is used to send the packets. + + (#) Once the application has received the last message associated with a call, + the tag is guaranteed not to be seen again, and so it can be used to pin + client resources. A new call can then be initiated with the same tag + without fear of interference. + + (#) In the server, a request is received with one or more recvmsgs, then the + the reply is transmitted with one or more sendmsgs, and then the final ACK + is received with a last recvmsg. + + (#) When sending data for a call, sendmsg is given MSG_MORE if there's more + data to come on that call. + + (#) When receiving data for a call, recvmsg flags MSG_MORE if there's more + data to come for that call. + + (#) When receiving data or messages for a call, MSG_EOR is flagged by recvmsg + to indicate the terminal message for that call. + + (#) A call may be aborted by adding an abort control message to the control + data. Issuing an abort terminates the kernel's use of that call's tag. + Any messages waiting in the receive queue for that call will be discarded. + + (#) Aborts, busy notifications and challenge packets are delivered by recvmsg, + and control data messages will be set to indicate the context. Receiving + an abort or a busy message terminates the kernel's use of that call's tag. + + (#) The control data part of the msghdr struct is used for a number of things: + + (#) The tag of the intended or affected call. + + (#) Sending or receiving errors, aborts and busy notifications. + + (#) Notifications of incoming calls. + + (#) Sending debug requests and receiving debug replies [TODO]. + + (#) When the kernel has received and set up an incoming call, it sends a + message to server application to let it know there's a new call awaiting + its acceptance [recvmsg reports a special control message]. The server + application then uses sendmsg to assign a tag to the new call. Once that + is done, the first part of the request data will be delivered by recvmsg. + + (#) The server application has to provide the server socket with a keyring of + secret keys corresponding to the security types it permits. When a secure + connection is being set up, the kernel looks up the appropriate secret key + in the keyring and then sends a challenge packet to the client and + receives a response packet. The kernel then checks the authorisation of + the packet and either aborts the connection or sets up the security. + + (#) The name of the key a client will use to secure its communications is + nominated by a socket option. + + +Notes on sendmsg: + + (#) MSG_WAITALL can be set to tell sendmsg to ignore signals if the peer is + making progress at accepting packets within a reasonable time such that we + manage to queue up all the data for transmission. This requires the + client to accept at least one packet per 2*RTT time period. + + If this isn't set, sendmsg() will return immediately, either returning + EINTR/ERESTARTSYS if nothing was consumed or returning the amount of data + consumed. + + +Notes on recvmsg: + + (#) If there's a sequence of data messages belonging to a particular call on + the receive queue, then recvmsg will keep working through them until: + + (a) it meets the end of that call's received data, + + (b) it meets a non-data message, + + (c) it meets a message belonging to a different call, or + + (d) it fills the user buffer. + + If recvmsg is called in blocking mode, it will keep sleeping, awaiting the + reception of further data, until one of the above four conditions is met. + + (2) MSG_PEEK operates similarly, but will return immediately if it has put any + data in the buffer rather than sleeping until it can fill the buffer. + + (3) If a data message is only partially consumed in filling a user buffer, + then the remainder of that message will be left on the front of the queue + for the next taker. MSG_TRUNC will never be flagged. + + (4) If there is more data to be had on a call (it hasn't copied the last byte + of the last data message in that phase yet), then MSG_MORE will be + flagged. + + +Control Messages +================ + +AF_RXRPC makes use of control messages in sendmsg() and recvmsg() to multiplex +calls, to invoke certain actions and to report certain conditions. These are: + + ======================= === =========== =============================== + MESSAGE ID SRT DATA MEANING + ======================= === =========== =============================== + RXRPC_USER_CALL_ID sr- User ID App's call specifier + RXRPC_ABORT srt Abort code Abort code to issue/received + RXRPC_ACK -rt n/a Final ACK received + RXRPC_NET_ERROR -rt error num Network error on call + RXRPC_BUSY -rt n/a Call rejected (server busy) + RXRPC_LOCAL_ERROR -rt error num Local error encountered + RXRPC_NEW_CALL -r- n/a New call received + RXRPC_ACCEPT s-- n/a Accept new call + RXRPC_EXCLUSIVE_CALL s-- n/a Make an exclusive client call + RXRPC_UPGRADE_SERVICE s-- n/a Client call can be upgraded + RXRPC_TX_LENGTH s-- data len Total length of Tx data + ======================= === =========== =============================== + + (SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message) + + (#) RXRPC_USER_CALL_ID + + This is used to indicate the application's call ID. It's an unsigned long + that the app specifies in the client by attaching it to the first data + message or in the server by passing it in association with an RXRPC_ACCEPT + message. recvmsg() passes it in conjunction with all messages except + those of the RXRPC_NEW_CALL message. + + (#) RXRPC_ABORT + + This is can be used by an application to abort a call by passing it to + sendmsg, or it can be delivered by recvmsg to indicate a remote abort was + received. Either way, it must be associated with an RXRPC_USER_CALL_ID to + specify the call affected. If an abort is being sent, then error EBADSLT + will be returned if there is no call with that user ID. + + (#) RXRPC_ACK + + This is delivered to a server application to indicate that the final ACK + of a call was received from the client. It will be associated with an + RXRPC_USER_CALL_ID to indicate the call that's now complete. + + (#) RXRPC_NET_ERROR + + This is delivered to an application to indicate that an ICMP error message + was encountered in the process of trying to talk to the peer. An + errno-class integer value will be included in the control message data + indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call + affected. + + (#) RXRPC_BUSY + + This is delivered to a client application to indicate that a call was + rejected by the server due to the server being busy. It will be + associated with an RXRPC_USER_CALL_ID to indicate the rejected call. + + (#) RXRPC_LOCAL_ERROR + + This is delivered to an application to indicate that a local error was + encountered and that a call has been aborted because of it. An + errno-class integer value will be included in the control message data + indicating the problem, and an RXRPC_USER_CALL_ID will indicate the call + affected. + + (#) RXRPC_NEW_CALL + + This is delivered to indicate to a server application that a new call has + arrived and is awaiting acceptance. No user ID is associated with this, + as a user ID must subsequently be assigned by doing an RXRPC_ACCEPT. + + (#) RXRPC_ACCEPT + + This is used by a server application to attempt to accept a call and + assign it a user ID. It should be associated with an RXRPC_USER_CALL_ID + to indicate the user ID to be assigned. If there is no call to be + accepted (it may have timed out, been aborted, etc.), then sendmsg will + return error ENODATA. If the user ID is already in use by another call, + then error EBADSLT will be returned. + + (#) RXRPC_EXCLUSIVE_CALL + + This is used to indicate that a client call should be made on a one-off + connection. The connection is discarded once the call has terminated. + + (#) RXRPC_UPGRADE_SERVICE + + This is used to make a client call to probe if the specified service ID + may be upgraded by the server. The caller must check msg_name returned to + recvmsg() for the service ID actually in use. The operation probed must + be one that takes the same arguments in both services. + + Once this has been used to establish the upgrade capability (or lack + thereof) of the server, the service ID returned should be used for all + future communication to that server and RXRPC_UPGRADE_SERVICE should no + longer be set. + + (#) RXRPC_TX_LENGTH + + This is used to inform the kernel of the total amount of data that is + going to be transmitted by a call (whether in a client request or a + service response). If given, it allows the kernel to encrypt from the + userspace buffer directly to the packet buffers, rather than copying into + the buffer and then encrypting in place. This may only be given with the + first sendmsg() providing data for a call. EMSGSIZE will be generated if + the amount of data actually given is different. + + This takes a parameter of __s64 type that indicates how much will be + transmitted. This may not be less than zero. + +The symbol RXRPC__SUPPORTED is defined as one more than the highest control +message type supported. At run time this can be queried by means of the +RXRPC_SUPPORTED_CMSG socket option (see below). + + +============== +SOCKET OPTIONS +============== + +AF_RXRPC sockets support a few socket options at the SOL_RXRPC level: + + (#) RXRPC_SECURITY_KEY + + This is used to specify the description of the key to be used. The key is + extracted from the calling process's keyrings with request_key() and + should be of "rxrpc" type. + + The optval pointer points to the description string, and optlen indicates + how long the string is, without the NUL terminator. + + (#) RXRPC_SECURITY_KEYRING + + Similar to above but specifies a keyring of server secret keys to use (key + type "keyring"). See the "Security" section. + + (#) RXRPC_EXCLUSIVE_CONNECTION + + This is used to request that new connections should be used for each call + made subsequently on this socket. optval should be NULL and optlen 0. + + (#) RXRPC_MIN_SECURITY_LEVEL + + This is used to specify the minimum security level required for calls on + this socket. optval must point to an int containing one of the following + values: + + (a) RXRPC_SECURITY_PLAIN + + Encrypted checksum only. + + (b) RXRPC_SECURITY_AUTH + + Encrypted checksum plus packet padded and first eight bytes of packet + encrypted - which includes the actual packet length. + + (c) RXRPC_SECURITY_ENCRYPT + + Encrypted checksum plus entire packet padded and encrypted, including + actual packet length. + + (#) RXRPC_UPGRADEABLE_SERVICE + + This is used to indicate that a service socket with two bindings may + upgrade one bound service to the other if requested by the client. optval + must point to an array of two unsigned short ints. The first is the + service ID to upgrade from and the second the service ID to upgrade to. + + (#) RXRPC_SUPPORTED_CMSG + + This is a read-only option that writes an int into the buffer indicating + the highest control message type supported. + + +======== +SECURITY +======== + +Currently, only the kerberos 4 equivalent protocol has been implemented +(security index 2 - rxkad). This requires the rxkad module to be loaded and, +on the client, tickets of the appropriate type to be obtained from the AFS +kaserver or the kerberos server and installed as "rxrpc" type keys. This is +normally done using the klog program. An example simple klog program can be +found at: + + http://people.redhat.com/~dhowells/rxrpc/klog.c + +The payload provided to add_key() on the client should be of the following +form:: + + struct rxrpc_key_sec2_v1 { + uint16_t security_index; /* 2 */ + uint16_t ticket_length; /* length of ticket[] */ + uint32_t expiry; /* time at which expires */ + uint8_t kvno; /* key version number */ + uint8_t __pad[3]; + uint8_t session_key[8]; /* DES session key */ + uint8_t ticket[0]; /* the encrypted ticket */ + }; + +Where the ticket blob is just appended to the above structure. + + +For the server, keys of type "rxrpc_s" must be made available to the server. +They have a description of "<serviceID>:<securityIndex>" (eg: "52:2" for an +rxkad key for the AFS VL service). When such a key is created, it should be +given the server's secret key as the instantiation data (see the example +below). + + add_key("rxrpc_s", "52:2", secret_key, 8, keyring); + +A keyring is passed to the server socket by naming it in a sockopt. The server +socket then looks the server secret keys up in this keyring when secure +incoming connections are made. This can be seen in an example program that can +be found at: + + http://people.redhat.com/~dhowells/rxrpc/listen.c + + +==================== +EXAMPLE CLIENT USAGE +==================== + +A client would issue an operation by: + + (1) An RxRPC socket is set up by:: + + client = socket(AF_RXRPC, SOCK_DGRAM, PF_INET); + + Where the third parameter indicates the protocol family of the transport + socket used - usually IPv4 but it can also be IPv6 [TODO]. + + (2) A local address can optionally be bound:: + + struct sockaddr_rxrpc srx = { + .srx_family = AF_RXRPC, + .srx_service = 0, /* we're a client */ + .transport_type = SOCK_DGRAM, /* type of transport socket */ + .transport.sin_family = AF_INET, + .transport.sin_port = htons(7000), /* AFS callback */ + .transport.sin_address = 0, /* all local interfaces */ + }; + bind(client, &srx, sizeof(srx)); + + This specifies the local UDP port to be used. If not given, a random + non-privileged port will be used. A UDP port may be shared between + several unrelated RxRPC sockets. Security is handled on a basis of + per-RxRPC virtual connection. + + (3) The security is set:: + + const char *key = "AFS:cambridge.redhat.com"; + setsockopt(client, SOL_RXRPC, RXRPC_SECURITY_KEY, key, strlen(key)); + + This issues a request_key() to get the key representing the security + context. The minimum security level can be set:: + + unsigned int sec = RXRPC_SECURITY_ENCRYPT; + setsockopt(client, SOL_RXRPC, RXRPC_MIN_SECURITY_LEVEL, + &sec, sizeof(sec)); + + (4) The server to be contacted can then be specified (alternatively this can + be done through sendmsg):: + + struct sockaddr_rxrpc srx = { + .srx_family = AF_RXRPC, + .srx_service = VL_SERVICE_ID, + .transport_type = SOCK_DGRAM, /* type of transport socket */ + .transport.sin_family = AF_INET, + .transport.sin_port = htons(7005), /* AFS volume manager */ + .transport.sin_address = ..., + }; + connect(client, &srx, sizeof(srx)); + + (5) The request data should then be posted to the server socket using a series + of sendmsg() calls, each with the following control message attached: + + ================== =================================== + RXRPC_USER_CALL_ID specifies the user ID for this call + ================== =================================== + + MSG_MORE should be set in msghdr::msg_flags on all but the last part of + the request. Multiple requests may be made simultaneously. + + An RXRPC_TX_LENGTH control message can also be specified on the first + sendmsg() call. + + If a call is intended to go to a destination other than the default + specified through connect(), then msghdr::msg_name should be set on the + first request message of that call. + + (6) The reply data will then be posted to the server socket for recvmsg() to + pick up. MSG_MORE will be flagged by recvmsg() if there's more reply data + for a particular call to be read. MSG_EOR will be set on the terminal + read for a call. + + All data will be delivered with the following control message attached: + + RXRPC_USER_CALL_ID - specifies the user ID for this call + + If an abort or error occurred, this will be returned in the control data + buffer instead, and MSG_EOR will be flagged to indicate the end of that + call. + +A client may ask for a service ID it knows and ask that this be upgraded to a +better service if one is available by supplying RXRPC_UPGRADE_SERVICE on the +first sendmsg() of a call. The client should then check srx_service in the +msg_name filled in by recvmsg() when collecting the result. srx_service will +hold the same value as given to sendmsg() if the upgrade request was ignored by +the service - otherwise it will be altered to indicate the service ID the +server upgraded to. Note that the upgraded service ID is chosen by the server. +The caller has to wait until it sees the service ID in the reply before sending +any more calls (further calls to the same destination will be blocked until the +probe is concluded). + + +Example Server Usage +==================== + +A server would be set up to accept operations in the following manner: + + (1) An RxRPC socket is created by:: + + server = socket(AF_RXRPC, SOCK_DGRAM, PF_INET); + + Where the third parameter indicates the address type of the transport + socket used - usually IPv4. + + (2) Security is set up if desired by giving the socket a keyring with server + secret keys in it:: + + keyring = add_key("keyring", "AFSkeys", NULL, 0, + KEY_SPEC_PROCESS_KEYRING); + + const char secret_key[8] = { + 0xa7, 0x83, 0x8a, 0xcb, 0xc7, 0x83, 0xec, 0x94 }; + add_key("rxrpc_s", "52:2", secret_key, 8, keyring); + + setsockopt(server, SOL_RXRPC, RXRPC_SECURITY_KEYRING, "AFSkeys", 7); + + The keyring can be manipulated after it has been given to the socket. This + permits the server to add more keys, replace keys, etc. while it is live. + + (3) A local address must then be bound:: + + struct sockaddr_rxrpc srx = { + .srx_family = AF_RXRPC, + .srx_service = VL_SERVICE_ID, /* RxRPC service ID */ + .transport_type = SOCK_DGRAM, /* type of transport socket */ + .transport.sin_family = AF_INET, + .transport.sin_port = htons(7000), /* AFS callback */ + .transport.sin_address = 0, /* all local interfaces */ + }; + bind(server, &srx, sizeof(srx)); + + More than one service ID may be bound to a socket, provided the transport + parameters are the same. The limit is currently two. To do this, bind() + should be called twice. + + (4) If service upgrading is required, first two service IDs must have been + bound and then the following option must be set:: + + unsigned short service_ids[2] = { from_ID, to_ID }; + setsockopt(server, SOL_RXRPC, RXRPC_UPGRADEABLE_SERVICE, + service_ids, sizeof(service_ids)); + + This will automatically upgrade connections on service from_ID to service + to_ID if they request it. This will be reflected in msg_name obtained + through recvmsg() when the request data is delivered to userspace. + + (5) The server is then set to listen out for incoming calls:: + + listen(server, 100); + + (6) The kernel notifies the server of pending incoming connections by sending + it a message for each. This is received with recvmsg() on the server + socket. It has no data, and has a single dataless control message + attached:: + + RXRPC_NEW_CALL + + The address that can be passed back by recvmsg() at this point should be + ignored since the call for which the message was posted may have gone by + the time it is accepted - in which case the first call still on the queue + will be accepted. + + (7) The server then accepts the new call by issuing a sendmsg() with two + pieces of control data and no actual data: + + ================== ============================== + RXRPC_ACCEPT indicate connection acceptance + RXRPC_USER_CALL_ID specify user ID for this call + ================== ============================== + + (8) The first request data packet will then be posted to the server socket for + recvmsg() to pick up. At that point, the RxRPC address for the call can + be read from the address fields in the msghdr struct. + + Subsequent request data will be posted to the server socket for recvmsg() + to collect as it arrives. All but the last piece of the request data will + be delivered with MSG_MORE flagged. + + All data will be delivered with the following control message attached: + + + ================== =================================== + RXRPC_USER_CALL_ID specifies the user ID for this call + ================== =================================== + + (9) The reply data should then be posted to the server socket using a series + of sendmsg() calls, each with the following control messages attached: + + ================== =================================== + RXRPC_USER_CALL_ID specifies the user ID for this call + ================== =================================== + + MSG_MORE should be set in msghdr::msg_flags on all but the last message + for a particular call. + +(10) The final ACK from the client will be posted for retrieval by recvmsg() + when it is received. It will take the form of a dataless message with two + control messages attached: + + ================== =================================== + RXRPC_USER_CALL_ID specifies the user ID for this call + RXRPC_ACK indicates final ACK (no data) + ================== =================================== + + MSG_EOR will be flagged to indicate that this is the final message for + this call. + +(11) Up to the point the final packet of reply data is sent, the call can be + aborted by calling sendmsg() with a dataless message with the following + control messages attached: + + ================== =================================== + RXRPC_USER_CALL_ID specifies the user ID for this call + RXRPC_ABORT indicates abort code (4 byte data) + ================== =================================== + + Any packets waiting in the socket's receive queue will be discarded if + this is issued. + +Note that all the communications for a particular service take place through +the one server socket, using control messages on sendmsg() and recvmsg() to +determine the call affected. + + +AF_RXRPC Kernel Interface +========================= + +The AF_RXRPC module also provides an interface for use by in-kernel utilities +such as the AFS filesystem. This permits such a utility to: + + (1) Use different keys directly on individual client calls on one socket + rather than having to open a whole slew of sockets, one for each key it + might want to use. + + (2) Avoid having RxRPC call request_key() at the point of issue of a call or + opening of a socket. Instead the utility is responsible for requesting a + key at the appropriate point. AFS, for instance, would do this during VFS + operations such as open() or unlink(). The key is then handed through + when the call is initiated. + + (3) Request the use of something other than GFP_KERNEL to allocate memory. + + (4) Avoid the overhead of using the recvmsg() call. RxRPC messages can be + intercepted before they get put into the socket Rx queue and the socket + buffers manipulated directly. + +To use the RxRPC facility, a kernel utility must still open an AF_RXRPC socket, +bind an address as appropriate and listen if it's to be a server socket, but +then it passes this to the kernel interface functions. + +The kernel interface functions are as follows: + + (#) Begin a new client call:: + + struct rxrpc_call * + rxrpc_kernel_begin_call(struct socket *sock, + struct sockaddr_rxrpc *srx, + struct key *key, + unsigned long user_call_ID, + s64 tx_total_len, + gfp_t gfp, + rxrpc_notify_rx_t notify_rx, + bool upgrade, + bool intr, + unsigned int debug_id); + + This allocates the infrastructure to make a new RxRPC call and assigns + call and connection numbers. The call will be made on the UDP port that + the socket is bound to. The call will go to the destination address of a + connected client socket unless an alternative is supplied (srx is + non-NULL). + + If a key is supplied then this will be used to secure the call instead of + the key bound to the socket with the RXRPC_SECURITY_KEY sockopt. Calls + secured in this way will still share connections if at all possible. + + The user_call_ID is equivalent to that supplied to sendmsg() in the + control data buffer. It is entirely feasible to use this to point to a + kernel data structure. + + tx_total_len is the amount of data the caller is intending to transmit + with this call (or -1 if unknown at this point). Setting the data size + allows the kernel to encrypt directly to the packet buffers, thereby + saving a copy. The value may not be less than -1. + + notify_rx is a pointer to a function to be called when events such as + incoming data packets or remote aborts happen. + + upgrade should be set to true if a client operation should request that + the server upgrade the service to a better one. The resultant service ID + is returned by rxrpc_kernel_recv_data(). + + intr should be set to true if the call should be interruptible. If this + is not set, this function may not return until a channel has been + allocated; if it is set, the function may return -ERESTARTSYS. + + debug_id is the call debugging ID to be used for tracing. This can be + obtained by atomically incrementing rxrpc_debug_id. + + If this function is successful, an opaque reference to the RxRPC call is + returned. The caller now holds a reference on this and it must be + properly ended. + + (#) End a client call:: + + void rxrpc_kernel_end_call(struct socket *sock, + struct rxrpc_call *call); + + This is used to end a previously begun call. The user_call_ID is expunged + from AF_RXRPC's knowledge and will not be seen again in association with + the specified call. + + (#) Send data through a call:: + + typedef void (*rxrpc_notify_end_tx_t)(struct sock *sk, + unsigned long user_call_ID, + struct sk_buff *skb); + + int rxrpc_kernel_send_data(struct socket *sock, + struct rxrpc_call *call, + struct msghdr *msg, + size_t len, + rxrpc_notify_end_tx_t notify_end_rx); + + This is used to supply either the request part of a client call or the + reply part of a server call. msg.msg_iovlen and msg.msg_iov specify the + data buffers to be used. msg_iov may not be NULL and must point + exclusively to in-kernel virtual addresses. msg.msg_flags may be given + MSG_MORE if there will be subsequent data sends for this call. + + The msg must not specify a destination address, control data or any flags + other than MSG_MORE. len is the total amount of data to transmit. + + notify_end_rx can be NULL or it can be used to specify a function to be + called when the call changes state to end the Tx phase. This function is + called with the call-state spinlock held to prevent any reply or final ACK + from being delivered first. + + (#) Receive data from a call:: + + int rxrpc_kernel_recv_data(struct socket *sock, + struct rxrpc_call *call, + void *buf, + size_t size, + size_t *_offset, + bool want_more, + u32 *_abort, + u16 *_service) + + This is used to receive data from either the reply part of a client call + or the request part of a service call. buf and size specify how much + data is desired and where to store it. *_offset is added on to buf and + subtracted from size internally; the amount copied into the buffer is + added to *_offset before returning. + + want_more should be true if further data will be required after this is + satisfied and false if this is the last item of the receive phase. + + There are three normal returns: 0 if the buffer was filled and want_more + was true; 1 if the buffer was filled, the last DATA packet has been + emptied and want_more was false; and -EAGAIN if the function needs to be + called again. + + If the last DATA packet is processed but the buffer contains less than + the amount requested, EBADMSG is returned. If want_more wasn't set, but + more data was available, EMSGSIZE is returned. + + If a remote ABORT is detected, the abort code received will be stored in + ``*_abort`` and ECONNABORTED will be returned. + + The service ID that the call ended up with is returned into *_service. + This can be used to see if a call got a service upgrade. + + (#) Abort a call?? + + :: + + void rxrpc_kernel_abort_call(struct socket *sock, + struct rxrpc_call *call, + u32 abort_code); + + This is used to abort a call if it's still in an abortable state. The + abort code specified will be placed in the ABORT message sent. + + (#) Intercept received RxRPC messages:: + + typedef void (*rxrpc_interceptor_t)(struct sock *sk, + unsigned long user_call_ID, + struct sk_buff *skb); + + void + rxrpc_kernel_intercept_rx_messages(struct socket *sock, + rxrpc_interceptor_t interceptor); + + This installs an interceptor function on the specified AF_RXRPC socket. + All messages that would otherwise wind up in the socket's Rx queue are + then diverted to this function. Note that care must be taken to process + the messages in the right order to maintain DATA message sequentiality. + + The interceptor function itself is provided with the address of the socket + and handling the incoming message, the ID assigned by the kernel utility + to the call and the socket buffer containing the message. + + The skb->mark field indicates the type of message: + + =============================== ======================================= + Mark Meaning + =============================== ======================================= + RXRPC_SKB_MARK_DATA Data message + RXRPC_SKB_MARK_FINAL_ACK Final ACK received for an incoming call + RXRPC_SKB_MARK_BUSY Client call rejected as server busy + RXRPC_SKB_MARK_REMOTE_ABORT Call aborted by peer + RXRPC_SKB_MARK_NET_ERROR Network error detected + RXRPC_SKB_MARK_LOCAL_ERROR Local error encountered + RXRPC_SKB_MARK_NEW_CALL New incoming call awaiting acceptance + =============================== ======================================= + + The remote abort message can be probed with rxrpc_kernel_get_abort_code(). + The two error messages can be probed with rxrpc_kernel_get_error_number(). + A new call can be accepted with rxrpc_kernel_accept_call(). + + Data messages can have their contents extracted with the usual bunch of + socket buffer manipulation functions. A data message can be determined to + be the last one in a sequence with rxrpc_kernel_is_data_last(). When a + data message has been used up, rxrpc_kernel_data_consumed() should be + called on it. + + Messages should be handled to rxrpc_kernel_free_skb() to dispose of. It + is possible to get extra refs on all types of message for later freeing, + but this may pin the state of a call until the message is finally freed. + + (#) Accept an incoming call:: + + struct rxrpc_call * + rxrpc_kernel_accept_call(struct socket *sock, + unsigned long user_call_ID); + + This is used to accept an incoming call and to assign it a call ID. This + function is similar to rxrpc_kernel_begin_call() and calls accepted must + be ended in the same way. + + If this function is successful, an opaque reference to the RxRPC call is + returned. The caller now holds a reference on this and it must be + properly ended. + + (#) Reject an incoming call:: + + int rxrpc_kernel_reject_call(struct socket *sock); + + This is used to reject the first incoming call on the socket's queue with + a BUSY message. -ENODATA is returned if there were no incoming calls. + Other errors may be returned if the call had been aborted (-ECONNABORTED) + or had timed out (-ETIME). + + (#) Allocate a null key for doing anonymous security:: + + struct key *rxrpc_get_null_key(const char *keyname); + + This is used to allocate a null RxRPC key that can be used to indicate + anonymous security for a particular domain. + + (#) Get the peer address of a call:: + + void rxrpc_kernel_get_peer(struct socket *sock, struct rxrpc_call *call, + struct sockaddr_rxrpc *_srx); + + This is used to find the remote peer address of a call. + + (#) Set the total transmit data size on a call:: + + void rxrpc_kernel_set_tx_length(struct socket *sock, + struct rxrpc_call *call, + s64 tx_total_len); + + This sets the amount of data that the caller is intending to transmit on a + call. It's intended to be used for setting the reply size as the request + size should be set when the call is begun. tx_total_len may not be less + than zero. + + (#) Get call RTT:: + + u64 rxrpc_kernel_get_rtt(struct socket *sock, struct rxrpc_call *call); + + Get the RTT time to the peer in use by a call. The value returned is in + nanoseconds. + + (#) Check call still alive:: + + bool rxrpc_kernel_check_life(struct socket *sock, + struct rxrpc_call *call, + u32 *_life); + void rxrpc_kernel_probe_life(struct socket *sock, + struct rxrpc_call *call); + + The first function passes back in ``*_life`` a number that is updated when + ACKs are received from the peer (notably including PING RESPONSE ACKs + which we can elicit by sending PING ACKs to see if the call still exists + on the server). The caller should compare the numbers of two calls to see + if the call is still alive after waiting for a suitable interval. It also + returns true as long as the call hasn't yet reached the completed state. + + This allows the caller to work out if the server is still contactable and + if the call is still alive on the server while waiting for the server to + process a client operation. + + The second function causes a ping ACK to be transmitted to try to provoke + the peer into responding, which would then cause the value returned by the + first function to change. Note that this must be called in TASK_RUNNING + state. + + (#) Get reply timestamp:: + + bool rxrpc_kernel_get_reply_time(struct socket *sock, + struct rxrpc_call *call, + ktime_t *_ts) + + This allows the timestamp on the first DATA packet of the reply of a + client call to be queried, provided that it is still in the Rx ring. If + successful, the timestamp will be stored into ``*_ts`` and true will be + returned; false will be returned otherwise. + + (#) Get remote client epoch:: + + u32 rxrpc_kernel_get_epoch(struct socket *sock, + struct rxrpc_call *call) + + This allows the epoch that's contained in packets of an incoming client + call to be queried. This value is returned. The function always + successful if the call is still in progress. It shouldn't be called once + the call has expired. Note that calling this on a local client call only + returns the local epoch. + + This value can be used to determine if the remote client has been + restarted as it shouldn't change otherwise. + + (#) Set the maxmimum lifespan on a call:: + + void rxrpc_kernel_set_max_life(struct socket *sock, + struct rxrpc_call *call, + unsigned long hard_timeout) + + This sets the maximum lifespan on a call to hard_timeout (which is in + jiffies). In the event of the timeout occurring, the call will be + aborted and -ETIME or -ETIMEDOUT will be returned. + + (#) Apply the RXRPC_MIN_SECURITY_LEVEL sockopt to a socket from within in the + kernel:: + + int rxrpc_sock_set_min_security_level(struct sock *sk, + unsigned int val); + + This specifies the minimum security level required for calls on this + socket. + + +Configurable Parameters +======================= + +The RxRPC protocol driver has a number of configurable parameters that can be +adjusted through sysctls in /proc/net/rxrpc/: + + (#) req_ack_delay + + The amount of time in milliseconds after receiving a packet with the + request-ack flag set before we honour the flag and actually send the + requested ack. + + Usually the other side won't stop sending packets until the advertised + reception window is full (to a maximum of 255 packets), so delaying the + ACK permits several packets to be ACK'd in one go. + + (#) soft_ack_delay + + The amount of time in milliseconds after receiving a new packet before we + generate a soft-ACK to tell the sender that it doesn't need to resend. + + (#) idle_ack_delay + + The amount of time in milliseconds after all the packets currently in the + received queue have been consumed before we generate a hard-ACK to tell + the sender it can free its buffers, assuming no other reason occurs that + we would send an ACK. + + (#) resend_timeout + + The amount of time in milliseconds after transmitting a packet before we + transmit it again, assuming no ACK is received from the receiver telling + us they got it. + + (#) max_call_lifetime + + The maximum amount of time in seconds that a call may be in progress + before we preemptively kill it. + + (#) dead_call_expiry + + The amount of time in seconds before we remove a dead call from the call + list. Dead calls are kept around for a little while for the purpose of + repeating ACK and ABORT packets. + + (#) connection_expiry + + The amount of time in seconds after a connection was last used before we + remove it from the connection list. While a connection is in existence, + it serves as a placeholder for negotiated security; when it is deleted, + the security must be renegotiated. + + (#) transport_expiry + + The amount of time in seconds after a transport was last used before we + remove it from the transport list. While a transport is in existence, it + serves to anchor the peer data and keeps the connection ID counter. + + (#) rxrpc_rx_window_size + + The size of the receive window in packets. This is the maximum number of + unconsumed received packets we're willing to hold in memory for any + particular call. + + (#) rxrpc_rx_mtu + + The maximum packet MTU size that we're willing to receive in bytes. This + indicates to the peer whether we're willing to accept jumbo packets. + + (#) rxrpc_rx_jumbo_max + + The maximum number of packets that we're willing to accept in a jumbo + packet. Non-terminal packets in a jumbo packet must contain a four byte + header plus exactly 1412 bytes of data. The terminal packet must contain + a four byte header plus any amount of data. In any event, a jumbo packet + may not exceed rxrpc_rx_mtu in size. |