rxrpc: Note cksum in txbuf

Add a field to rxrpc_txbuf in which to store the checksum to go in the
header as this may get overwritten in the wire header struct when
transmitting as part of a jumbo packet.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org

net/rxrpc/ar-internal.h

@@ -803,6 +803,7 @@ struct rxrpc_txbuf {
 	unsigned int		flags;
 #define RXRPC_TXBUF_WIRE_FLAGS	0xff		/* The wire protocol flags */
 #define RXRPC_TXBUF_RESENT	0x100		/* Set if has been resent */
+	__be16			cksum;		/* Checksum to go in header */
 	u8 /*enum rxrpc_propose_ack_trace*/ ack_why;	/* If ack, why */
 	struct {
 		/* The packet for encrypting and DMA'ing.  We align it such

net/rxrpc/output.c

@@ -335,6 +335,7 @@ int rxrpc_send_data_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
 	/* Each transmission of a Tx packet+ needs a new serial number */
 	txb->serial = rxrpc_get_next_serial(conn);
 	txb->wire.serial = htonl(txb->serial);
+	txb->wire.cksum = txb->cksum;
 
 	if (test_bit(RXRPC_CONN_PROBING_FOR_UPGRADE, &conn->flags) &&
 	    txb->seq == 1)

net/rxrpc/rxkad.c

@@ -378,7 +378,7 @@ static int rxkad_secure_packet(struct rxrpc_call *call, struct rxrpc_txbuf *txb)
 	y = (y >> 16) & 0xffff;
 	if (y == 0)
 		y = 1; /* zero checksums are not permitted */
-	txb->wire.cksum = htons(y);
+	txb->cksum = htons(y);
 
 	switch (call->conn->security_level) {
 	case RXRPC_SECURITY_PLAIN:

net/rxrpc/txbuf.c

@@ -35,6 +35,7 @@ struct rxrpc_txbuf *rxrpc_alloc_txbuf(struct rxrpc_call *call, u8 packet_type,
 		txb->ack_why		= 0;
 		txb->seq		= call->tx_prepared + 1;
 		txb->serial		= 0;
+		txb->cksum		= 0;
 		txb->wire.epoch		= htonl(call->conn->proto.epoch);
 		txb->wire.cid		= htonl(call->cid);
 		txb->wire.callNumber	= htonl(call->call_id);