rxrpc: Provide functions for allowing cleaner handling of signals

Provide a couple of functions to allow cleaner handling of signals in a
kernel service.  They are:

 (1) rxrpc_kernel_get_rtt()

     This allows the kernel service to find out the RTT time for a call, so
     as to better judge how large a timeout to employ.

     Note, though, that whilst this returns a value in nanoseconds, the
     timeouts can only actually be in jiffies.

 (2) rxrpc_kernel_check_life()

     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.

These can be used to provide an extending timeout rather than returning
immediately in the case that a signal occurs that would otherwise abort an
RPC operation.  The timeout would be extended if the server is still
responsive and the call is still apparently alive on the server.

For most operations this isn't that necessary - but for FS.StoreData it is:
OpenAFS writes the data to storage as it comes in without making a backup,
so if we immediately abort it when partially complete on a CTRL+C, say, we
have no idea of the state of the file after the abort.

Signed-off-by: David Howells <[email protected]>

net/rxrpc/af_rxrpc.c

@@ -339,6 +339,25 @@ void rxrpc_kernel_end_call(struct socket *sock, struct rxrpc_call *call)
 }
 EXPORT_SYMBOL(rxrpc_kernel_end_call);
 
+/**
+ * rxrpc_kernel_check_life - Check to see whether a call is still alive
+ * @sock: The socket the call is on
+ * @call: The call to check
+ *
+ * Allow a kernel service to find out whether a call is still alive - ie. we're
+ * getting ACKs from the server.  Returns a number representing the life state
+ * which can be compared to that returned by a previous call.
+ *
+ * If this is a client call, ping ACKs will be sent to the server to find out
+ * whether it's still responsive and whether the call is still alive on the
+ * server.
+ */
+u32 rxrpc_kernel_check_life(struct socket *sock, struct rxrpc_call *call)
+{
+	return call->acks_latest;
+}
+EXPORT_SYMBOL(rxrpc_kernel_check_life);
+
 /**
  * rxrpc_kernel_check_call - Check a call's state
  * @sock: The socket the call is on

net/rxrpc/peer_object.c

@@ -411,3 +411,16 @@ void rxrpc_kernel_get_peer(struct socket *sock, struct rxrpc_call *call,
 	*_srx = call->peer->srx;
 }
 EXPORT_SYMBOL(rxrpc_kernel_get_peer);
+
+/**
+ * rxrpc_kernel_get_rtt - Get a call's peer RTT
+ * @sock: The socket on which the call is in progress.
+ * @call: The call to query
+ *
+ * Get the call's peer RTT.
+ */
+u64 rxrpc_kernel_get_rtt(struct socket *sock, struct rxrpc_call *call)
+{
+	return call->peer->rtt;
+}
+EXPORT_SYMBOL(rxrpc_kernel_get_rtt);