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, 3 insertions, 2 deletions

diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index 104ee8b1de06..516d8ea82f02 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -136,6 +136,7 @@ static struct rxrpc_call *rxrpc_alloc_call(gfp_t gfp)
 	INIT_LIST_HEAD(&call->accept_link);
 	skb_queue_head_init(&call->rx_queue);
 	skb_queue_head_init(&call->rx_oos_queue);
+	skb_queue_head_init(&call->knlrecv_queue);
 	init_waitqueue_head(&call->waitq);
 	spin_lock_init(&call->lock);
 	rwlock_init(&call->state_lock);
@@ -552,8 +553,6 @@ void rxrpc_release_call(struct rxrpc_call *call)
 			spin_lock_bh(&call->lock);
 		}
 		spin_unlock_bh(&call->lock);
-
-		ASSERTCMP(call->state, !=, RXRPC_CALL_COMPLETE);
 	}
 
 	del_timer_sync(&call->resend_timer);
@@ -682,6 +681,7 @@ static void rxrpc_rcu_destroy_call(struct rcu_head *rcu)
 	struct rxrpc_call *call = container_of(rcu, struct rxrpc_call, rcu);
 
 	rxrpc_purge_queue(&call->rx_queue);
+	rxrpc_purge_queue(&call->knlrecv_queue);
 	rxrpc_put_peer(call->peer);
 	kmem_cache_free(rxrpc_call_jar, call);
 }
@@ -737,6 +737,7 @@ static void rxrpc_cleanup_call(struct rxrpc_call *call)
 
 	rxrpc_purge_queue(&call->rx_queue);
 	ASSERT(skb_queue_empty(&call->rx_oos_queue));
+	rxrpc_purge_queue(&call->knlrecv_queue);
 	sock_put(&call->socket->sk);
 	call_rcu(&call->rcu, rxrpc_rcu_destroy_call);
 }