rxrpc.txt

linux 内核源代码

	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.