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- ======================
- 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.
-
-
-========
-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 acknowledgement: 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 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
-
- (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.
-
-
-==============
-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_ENCRYPTED
-
- Encrypted checksum plus entire packet padded and encrypted, including
- actual packet length.
-
-
-========
-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_ENCRYPTED;
- 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.
-
- 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.
-
-
-====================
-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. whilst it is live.
-
- (2) 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));
-
- (3) The server is then set to listen out for incoming calls:
-
- listen(server, 100);
-
- (4) 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.
-
- (5) 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
-
- (6) 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
-
- (8) 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.
-
- (9) 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.
-
-(10) 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,
- gfp_t gfp);
-
- 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.
-
- 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 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.
-
- int rxrpc_kernel_send_data(struct rxrpc_call *call, struct msghdr *msg,
- size_t len);
-
- 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.
-
- (*) Abort a call.
-
- void rxrpc_kernel_abort_call(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_delivered() should be
- called on it..
-
- Non-data 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).
-
- (*) Record the delivery of a data message and free it.
-
- void rxrpc_kernel_data_delivered(struct sk_buff *skb);
-
- This is used to record a data message as having been delivered and to
- update the ACK state for the call. The socket buffer will be freed.
-
- (*) Free a message.
-
- void rxrpc_kernel_free_skb(struct sk_buff *skb);
-
- This is used to free a non-DATA socket buffer intercepted from an AF_RXRPC
- socket.
-
- (*) Determine if a data message is the last one on a call.
-
- bool rxrpc_kernel_is_data_last(struct sk_buff *skb);
-
- This is used to determine if a socket buffer holds the last data message
- to be received for a call (true will be returned if it does, false
- if not).
-
- The data message will be part of the reply on a client call and the
- request on an incoming call. In the latter case there will be more
- messages, but in the former case there will not.
-
- (*) Get the abort code from an abort message.
-
- u32 rxrpc_kernel_get_abort_code(struct sk_buff *skb);
-
- This is used to extract the abort code from a remote abort message.
-
- (*) Get the error number from a local or network error message.
-
- int rxrpc_kernel_get_error_number(struct sk_buff *skb);
-
- This is used to extract the error number from a message indicating either
- a local error occurred or a network error occurred.
-
- (*) 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.