net: introduce qemu_get_peer

This is a small function that can get the peer
from given NetClientState and queue_index

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20200701145538.22333-2-lulu@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

include/net/net.h

@@ -176,6 +176,7 @@ void hmp_info_network(Monitor *mon, const QDict *qdict);
 void net_socket_rs_init(SocketReadState *rs,
                         SocketReadStateFinalize *finalize,
                         bool vnet_hdr);
+NetClientState *qemu_get_peer(NetClientState *nc, int queue_index);
 
 /* NIC info */
 

net/net.c

@@ -325,6 +325,13 @@ void *qemu_get_nic_opaque(NetClientState *nc)
     return nic->opaque;
 }
 
+NetClientState *qemu_get_peer(NetClientState *nc, int queue_index)
+{
+    assert(nc != NULL);
+    NetClientState *ncs = nc + queue_index;
+    return ncs->peer;
+}
+
 static void qemu_cleanup_net_client(NetClientState *nc)
 {
     QTAILQ_REMOVE(&net_clients, nc, next);