rxrpc: Don't expose skbs to in-kernel users [ver #2]

Don't expose skbs to in-kernel users, such as the AFS filesystem, but
instead provide a notification hook the indicates that a call needs
attention and another that indicates that there's a new call to be
collected.

This makes the following possibilities more achievable:

 (1) Call refcounting can be made simpler if skbs don't hold refs to calls.

 (2) skbs referring to non-data events will be able to be freed much sooner
     rather than being queued for AFS to pick up as rxrpc_kernel_recv_data
     will be able to consult the call state.

 (3) We can shortcut the receive phase when a call is remotely aborted
     because we don't have to go through all the packets to get to the one
     cancelling the operation.

 (4) It makes it easier to do encryption/decryption directly between AFS's
     buffers and sk_buffs.

 (5) Encryption/decryption can more easily be done in the AFS's thread
     contexts - usually that of the userspace process that issued a syscall
     - rather than in one of rxrpc's background threads on a workqueue.

 (6) AFS will be able to wait synchronously on a call inside AF_RXRPC.

To make this work, the following interface function has been added:

     int rxrpc_kernel_recv_data(
		struct socket *sock, struct rxrpc_call *call,
		void *buffer, size_t bufsize, size_t *_offset,
		bool want_more, u32 *_abort_code);

This is the recvmsg equivalent.  It allows the caller to find out about the
state of a specific call and to transfer received data into a buffer
piecemeal.

afs_extract_data() and rxrpc_kernel_recv_data() now do all the extraction
logic between them.  They don't wait synchronously yet because the socket
lock needs to be dealt with.

Five interface functions have been removed:

	rxrpc_kernel_is_data_last()
    	rxrpc_kernel_get_abort_code()
    	rxrpc_kernel_get_error_number()
    	rxrpc_kernel_free_skb()
    	rxrpc_kernel_data_consumed()

As a temporary hack, sk_buffs going to an in-kernel call are queued on the
rxrpc_call struct (->knlrecv_queue) rather than being handed over to the
in-kernel user.  To process the queue internally, a temporary function,
temp_deliver_data() has been added.  This will be replaced with common code
between the rxrpc_recvmsg() path and the kernel_rxrpc_recv_data() path in a
future patch.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 31 insertions, 41 deletions

diff --git a/Documentation/networking/rxrpc.txt b/Documentation/networking/rxrpc.txt
index cfc8cb91452f..1b63bbc6b94f 100644
--- a/Documentation/networking/rxrpc.txt
+++ b/Documentation/networking/rxrpc.txt
@@ -748,6 +748,37 @@ The kernel interface functions are as follows:
      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.
 
+ (*) 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)
+
+      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.
+
  (*) Abort a call.
 
 	void rxrpc_kernel_abort_call(struct socket *sock,
@@ -825,47 +856,6 @@ The kernel interface functions are as follows:
      Other errors may be returned if the call had been aborted (-ECONNABORTED)
      or had timed out (-ETIME).
 
- (*) Record the delivery of a data message.
-
-	void rxrpc_kernel_data_consumed(struct rxrpc_call *call,
-					struct sk_buff *skb);
-
-     This is used to record a data message as having been consumed and to
-     update the ACK state for the call.  The message must still be passed to
-     rxrpc_kernel_free_skb() for disposal by the caller.
-
- (*) 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);