We are going to QOMify tap backend, which includes deriving TAPState
from Object. So "NetClientState nc" will not be a first member.
Let's parepare for this change, and use container_of(), which will
work regardless position of "nc" field.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 net/tap.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/net/tap.c b/net/tap.c
index 3a0a7a9f2ab..0679580fcaf 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -176,7 +176,7 @@ static ssize_t tap_write_packet(TAPState *s, const struct iovec *iov, int iovcnt
 static ssize_t tap_receive_iov(NetClientState *nc, const struct iovec *iov,
                                int iovcnt)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     const struct iovec *iovp = iov;
     g_autofree struct iovec *iov_copy = NULL;
     struct virtio_net_hdr hdr = { };
@@ -212,7 +212,7 @@ ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen)
 
 static void tap_send_completed(NetClientState *nc, ssize_t len)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     tap_read_poll(s, true);
 }
 
@@ -272,7 +272,7 @@ static void tap_send(void *opaque)
 
 static bool tap_has_ufo(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
 
@@ -281,7 +281,7 @@ static bool tap_has_ufo(NetClientState *nc)
 
 static bool tap_has_uso(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
 
@@ -290,7 +290,7 @@ static bool tap_has_uso(NetClientState *nc)
 
 static bool tap_has_tunnel(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
     return s->has_tunnel;
@@ -298,7 +298,7 @@ static bool tap_has_tunnel(NetClientState *nc)
 
 static bool tap_has_vnet_hdr(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
 
@@ -312,7 +312,7 @@ static bool tap_has_vnet_hdr_len(NetClientState *nc, int len)
 
 static void tap_set_vnet_hdr_len(NetClientState *nc, int len)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
 
@@ -323,21 +323,21 @@ static void tap_set_vnet_hdr_len(NetClientState *nc, int len)
 
 static int tap_set_vnet_le(NetClientState *nc, bool is_le)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     return tap_fd_set_vnet_le(s->fd, is_le);
 }
 
 static int tap_set_vnet_be(NetClientState *nc, bool is_be)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     return tap_fd_set_vnet_be(s->fd, is_be);
 }
 
 static void tap_set_offload(NetClientState *nc, const NetOffloads *ol)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     if (s->fd < 0) {
         return;
     }
@@ -358,7 +358,7 @@ static void tap_exit_notify(Notifier *notifier, void *data)
 
 static void tap_cleanup(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
 
     if (s->vhost_net) {
         vhost_net_cleanup(s->vhost_net);
@@ -382,14 +382,14 @@ static void tap_cleanup(NetClientState *nc)
 
 static void tap_poll(NetClientState *nc, bool enable)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     tap_read_poll(s, enable);
     tap_write_poll(s, enable);
 }
 
 static bool tap_set_steering_ebpf(NetClientState *nc, int prog_fd)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
 
     return tap_fd_set_steering_ebpf(s->fd, prog_fd) == 0;
@@ -397,7 +397,7 @@ static bool tap_set_steering_ebpf(NetClientState *nc, int prog_fd)
 
 int tap_get_fd(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
     return s->fd;
 }
@@ -409,7 +409,7 @@ int tap_get_fd(NetClientState *nc)
  */
 static VHostNetState *tap_get_vhost_net(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
     return s->vhost_net;
 }
@@ -448,7 +448,7 @@ static TAPState *net_tap_fd_init(NetClientState *peer,
 
     nc = qemu_new_net_client(&net_tap_info, peer, model, name);
 
-    s = DO_UPCAST(TAPState, nc, nc);
+    s = container_of(nc, TAPState, nc);
 
     s->fd = fd;
     s->host_vnet_hdr_len = vnet_hdr ? sizeof(struct virtio_net_hdr) : 0;
@@ -1017,7 +1017,7 @@ fail:
 
 int tap_enable(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     int ret;
 
     if (s->enabled) {
@@ -1034,7 +1034,7 @@ int tap_enable(NetClientState *nc)
 
 int tap_disable(NetClientState *nc)
 {
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    TAPState *s = container_of(nc, TAPState, nc);
     int ret;
 
     if (s->enabled == 0) {
-- 
2.43.0