• David Howells's avatar
    [AF_RXRPC]: Add an interface to the AF_RXRPC module for the AFS filesystem to use · 651350d1
    David Howells authored
    Add an interface to the AF_RXRPC module so that the AFS filesystem module can
    more easily make use of the services available.  AFS still opens a socket but
    then uses the action functions in lieu of sendmsg() and registers an intercept
    functions to grab messages before they're queued on the socket Rx queue.
    
    This permits AFS (or whatever) to:
    
     (1) Avoid the overhead of using the recvmsg() call.
    
     (2) 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.
    
     (3) Avoid calling request_key() at the point of issue of a call or opening of
         a socket.  This is done instead by AFS at the point of open(), unlink() or
         other VFS operation and the key handed through.
    
     (4) Request the use of something other than GFP_KERNEL to allocate memory.
    
    Furthermore:
    
     (*) The socket buffer markings used by RxRPC are made available for AFS so
         that it can interpret the cooked RxRPC messages itself.
    
     (*) rxgen (un)marshalling abort codes are made available.
    
    
    The following documentation for the kernel interface is added to
    Documentation/networking/rxrpc.txt:
    
    =========================
    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.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    651350d1
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