Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1149 insertions, 0 deletions

diff --git a/Documentation/networking/rxrpc.txt b/Documentation/networking/rxrpc.txt
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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.
+
+ (*) 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_ENCRYPTED
+
+	 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_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.
+
+     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. whilst 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);
+
+     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().
+
+     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.
+
+ (*) Check to see the completion state of a call so that the caller can assess
+     whether it needs to be retried.
+
+	enum rxrpc_call_completion {
+		RXRPC_CALL_SUCCEEDED,
+		RXRPC_CALL_REMOTELY_ABORTED,
+		RXRPC_CALL_LOCALLY_ABORTED,
+		RXRPC_CALL_LOCAL_ERROR,
+		RXRPC_CALL_NETWORK_ERROR,
+	};
+
+	int rxrpc_kernel_check_call(struct socket *sock, struct rxrpc_call *call,
+				    enum rxrpc_call_completion *_compl,
+				    u32 *_abort_code);
+
+     On return, -EINPROGRESS will be returned if the call is still ongoing; if
+     it is finished, *_compl will be set to indicate the manner of completion,
+     *_abort_code will be set to any abort code that occurred.  0 will be
+     returned on a successful completion, -ECONNABORTED will be returned if the
+     client failed due to a remote abort and anything else will return an
+     appropriate error code.
+
+     The caller should look at this information to decide if it's worth
+     retrying the call.
+
+ (*) Retry a client call.
+
+	int rxrpc_kernel_retry_call(struct socket *sock,
+				    struct rxrpc_call *call,
+				    struct sockaddr_rxrpc *srx,
+				    struct key *key);
+
+     This attempts to partially reinitialise a call and submit it again whilst
+     reusing the original call's Tx queue to avoid the need to repackage and
+     re-encrypt the data to be sent.  call indicates the call to retry, srx the
+     new address to send it to and key the encryption key to use for signing or
+     encrypting the packets.
+
+     For this to work, the first Tx data packet must still be in the transmit
+     queue, and currently this is only permitted for local and network errors
+     and the call must not have been aborted.  Any partially constructed Tx
+     packet is left as is and can continue being filled afterwards.
+
+     It returns 0 if the call was requeued and an error otherwise.
+
+ (*) 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.
+
+	u32 rxrpc_kernel_check_life(struct socket *sock,
+				    struct rxrpc_call *call);
+
+     This returns 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.
+
+     This allows the caller to work out if the server is still contactable and
+     if the call is still alive on the server whilst waiting for the server to
+     process a client operation.
+
+     This function may transmit a PING ACK.
+
+
+=======================
+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.  Whilst 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.  Whilst 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.