rxrpc: Allow the kernel to mark a call as being non-interruptible

Allow kernel services using AF_RXRPC to indicate that a call should be
non-interruptible.  This allows kafs to make things like lock-extension and
writeback data storage calls non-interruptible.

If this is set, signals will be ignored for operations on that call where
possible - such as waiting to get a call channel on an rxrpc connection.

It doesn't prevent UDP sendmsg from being interrupted, but that will be
handled by packet retransmission.

rxrpc_kernel_recv_data() isn't affected by this since that never waits,
preferring instead to return -EAGAIN and leave the waiting to the caller.

Userspace initiated calls can't be set to be uninterruptible at this time.

Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/af_rxrpc.c

@@ -270,6 +270,7 @@ static int rxrpc_listen(struct socket *sock, int backlog)
  * @gfp: The allocation constraints
  * @notify_rx: Where to send notifications instead of socket queue
  * @upgrade: Request service upgrade for call
+ * @intr: The call is interruptible
  * @debug_id: The debug ID for tracing to be assigned to the call
  *
  * Allow a kernel service to begin a call on the nominated socket.  This just
@@ -287,6 +288,7 @@ struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 					   gfp_t gfp,
 					   rxrpc_notify_rx_t notify_rx,
 					   bool upgrade,
+					   bool intr,
 					   unsigned int debug_id)
 {
 	struct rxrpc_conn_parameters cp;
@@ -311,6 +313,7 @@ struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 	memset(&p, 0, sizeof(p));
 	p.user_call_ID = user_call_ID;
 	p.tx_total_len = tx_total_len;
+	p.intr = intr;
 
 	memset(&cp, 0, sizeof(cp));
 	cp.local		= rx->local;