drbd: Introduce drbd_header_size()

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -315,6 +315,8 @@ struct p_header {
 	u8	  payload[0];
 };
 
+extern unsigned int drbd_header_size(struct drbd_tconn *tconn);
+
 /*
  * short commands, packets without payload, plain p_header:
  *   P_PING

drivers/block/drbd/drbd_main.c

@@ -689,6 +689,20 @@ void drbd_thread_current_set_cpu(struct drbd_thread *thi)
 }
 #endif
 
+/**
+ * drbd_header_size  -  size of a packet header
+ *
+ * The header size is a multiple of 8, so any payload following the header is
+ * word aligned on 64-bit architectures.  (The bitmap send and receive code
+ * relies on this.)
+ */
+unsigned int drbd_header_size(struct drbd_tconn *tconn)
+{
+	BUILD_BUG_ON(sizeof(struct p_header80) != sizeof(struct p_header95));
+	BUILD_BUG_ON(!IS_ALIGNED(sizeof(struct p_header80), 8));
+	return sizeof(struct p_header80);
+}
+
 static void prepare_header80(struct p_header80 *h, enum drbd_packet cmd, int size)
 {
 	h->magic   = cpu_to_be32(DRBD_MAGIC);

drivers/block/drbd/drbd_receiver.c

@@ -995,7 +995,7 @@ static int drbd_recv_header(struct drbd_tconn *tconn, struct packet_info *pi)
 	struct p_header *h = tconn->data.rbuf;
 	int err;
 
-	err = drbd_recv_all_warn(tconn, h, sizeof(*h));
+	err = drbd_recv_all_warn(tconn, h, drbd_header_size(tconn));
 	if (err)
 		return err;
 
@@ -4842,7 +4842,8 @@ int drbd_asender(struct drbd_thread *thi)
 	int rv;
 	void *buf    = h;
 	int received = 0;
-	int expect   = sizeof(struct p_header);
+	unsigned int header_size = drbd_header_size(tconn);
+	int expect   = header_size;
 	int ping_timeout_active = 0;
 
 	current->policy = SCHED_RR;  /* Make this a realtime task! */
@@ -4926,7 +4927,7 @@ int drbd_asender(struct drbd_thread *thi)
 				goto disconnect;
 			}
 			expect = cmd->pkt_size;
-			if (pi.size != expect - sizeof(struct p_header)) {
+			if (pi.size != expect - header_size) {
 				conn_err(tconn, "Wrong packet size on meta (c: %d, l: %d)\n",
 					pi.cmd, pi.size);
 				goto reconnect;
@@ -4950,7 +4951,7 @@ int drbd_asender(struct drbd_thread *thi)
 
 			buf	 = h;
 			received = 0;
-			expect	 = sizeof(struct p_header);
+			expect	 = header_size;
 			cmd	 = NULL;
 		}
 	}