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| -rw-r--r-- | Documentation/networking/rxrpc.txt | 196 |
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diff --git a/Documentation/networking/rxrpc.txt b/Documentation/networking/rxrpc.txt index fb809b738a0d..cae231b1c134 100644 --- a/Documentation/networking/rxrpc.txt +++ b/Documentation/networking/rxrpc.txt @@ -25,6 +25,8 @@ Contents of this document: (*) Example server usage. + (*) AF_RXRPC kernel interface. + ======== OVERVIEW @@ -661,3 +663,197 @@ A server would be set up to accept operations in the following manner: 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 addess 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. |