net: Add get_vhost_net callback to NetClientInfo

The get_vhost_net() function previously contained a large switch
statement to find the VHostNetState pointer based on the net
client's type. This created a tight coupling, requiring the generic
vhost layer to be aware of every specific backend that supported
vhost, such as tap, vhost-user, and vhost-vdpa.

This approach is not scalable and requires modifying a central function
for any new backend. It also forced each backend to expose its internal
getter function in a public header file.

This patch refactors the logic by introducing a new get_vhost_net
function pointer to the NetClientInfo struct. The central
get_vhost_net() function is now a simple, generic dispatcher that
invokes the callback provided by the net client.

Each backend now implements its own private getter and registers it in
its NetClientInfo.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/vhost_net.c

@@ -649,41 +649,18 @@ void vhost_net_config_mask(VHostNetState *net, VirtIODevice *dev, bool mask)
 {
     vhost_config_mask(&net->dev, dev, mask);
 }
+
 VHostNetState *get_vhost_net(NetClientState *nc)
 {
-    VHostNetState *vhost_net = 0;
-
     if (!nc) {
         return 0;
     }
 
-    switch (nc->info->type) {
-    case NET_CLIENT_DRIVER_TAP:
-        vhost_net = tap_get_vhost_net(nc);
-        /*
-         * tap_get_vhost_net() can return NULL if a tap net-device backend is
-         * created with 'vhost=off' option, 'vhostforce=off' or no vhost or
-         * vhostforce or vhostfd options at all. Please see net_init_tap_one().
-         * Hence, we omit the assertion here.
-         */
-        break;
-#ifdef CONFIG_VHOST_NET_USER
-    case NET_CLIENT_DRIVER_VHOST_USER:
-        vhost_net = vhost_user_get_vhost_net(nc);
-        assert(vhost_net);
-        break;
-#endif
-#ifdef CONFIG_VHOST_NET_VDPA
-    case NET_CLIENT_DRIVER_VHOST_VDPA:
-        vhost_net = vhost_vdpa_get_vhost_net(nc);
-        assert(vhost_net);
-        break;
-#endif
-    default:
-        break;
+    if (nc->info->get_vhost_net) {
+        return nc->info->get_vhost_net(nc);
     }
 
-    return vhost_net;
+    return NULL;
 }
 
 int vhost_net_set_vring_enable(NetClientState *nc, int enable)

include/net/net.h

@@ -67,6 +67,7 @@ typedef void (SocketReadStateFinalize)(SocketReadState *rs);
 typedef void (NetAnnounce)(NetClientState *);
 typedef bool (SetSteeringEBPF)(NetClientState *, int);
 typedef bool (NetCheckPeerType)(NetClientState *, ObjectClass *, Error **);
+typedef struct vhost_net *(GetVHostNet)(NetClientState *nc);
 
 typedef struct NetClientInfo {
     NetClientDriver type;
@@ -92,6 +93,7 @@ typedef struct NetClientInfo {
     NetAnnounce *announce;
     SetSteeringEBPF *set_steering_ebpf;
     NetCheckPeerType *check_peer_type;
+    GetVHostNet *get_vhost_net;
 } NetClientInfo;
 
 struct NetClientState {

include/net/tap.h

@@ -33,7 +33,4 @@ int tap_disable(NetClientState *nc);
 
 int tap_get_fd(NetClientState *nc);
 
-struct vhost_net;
-struct vhost_net *tap_get_vhost_net(NetClientState *nc);
-
 #endif /* QEMU_NET_TAP_H */

include/net/vhost-user.h

@@ -12,7 +12,6 @@
 #define VHOST_USER_H
 
 struct vhost_net;
-struct vhost_net *vhost_user_get_vhost_net(NetClientState *nc);
 uint64_t vhost_user_get_acked_features(NetClientState *nc);
 void vhost_user_save_acked_features(NetClientState *nc);
 

include/net/vhost-vdpa.h

@@ -14,8 +14,6 @@
 
 #define TYPE_VHOST_VDPA "vhost-vdpa"
 
-struct vhost_net *vhost_vdpa_get_vhost_net(NetClientState *nc);
-
 extern const int vdpa_feature_bits[];
 
 #endif /* VHOST_VDPA_H */

net/tap-win32.c

@@ -704,11 +704,6 @@ static void tap_win32_send(void *opaque)
     }
 }
 
-struct vhost_net *tap_get_vhost_net(NetClientState *nc)
-{
-    return NULL;
-}
-
 static NetClientInfo net_tap_win32_info = {
     .type = NET_CLIENT_DRIVER_TAP,
     .size = sizeof(TAPState),

net/tap.c

@@ -329,6 +329,18 @@ int tap_get_fd(NetClientState *nc)
     return s->fd;
 }
 
+/*
+ * tap_get_vhost_net() can return NULL if a tap net-device backend is
+ * created with 'vhost=off' option, 'vhostforce=off' or no vhost or
+ * vhostforce or vhostfd options at all. Please see net_init_tap_one().
+ */
+static VHostNetState *tap_get_vhost_net(NetClientState *nc)
+{
+    TAPState *s = DO_UPCAST(TAPState, nc, nc);
+    assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
+    return s->vhost_net;
+}
+
 /* fd support */
 
 static NetClientInfo net_tap_info = {
@@ -347,6 +359,7 @@ static NetClientInfo net_tap_info = {
     .set_vnet_le = tap_set_vnet_le,
     .set_vnet_be = tap_set_vnet_be,
     .set_steering_ebpf = tap_set_steering_ebpf,
+    .get_vhost_net = tap_get_vhost_net,
 };
 
 static TAPState *net_tap_fd_init(NetClientState *peer,
@@ -980,13 +993,6 @@ free_fail:
     return 0;
 }
 
-VHostNetState *tap_get_vhost_net(NetClientState *nc)
-{
-    TAPState *s = DO_UPCAST(TAPState, nc, nc);
-    assert(nc->info->type == NET_CLIENT_DRIVER_TAP);
-    return s->vhost_net;
-}
-
 int tap_enable(NetClientState *nc)
 {
     TAPState *s = DO_UPCAST(TAPState, nc, nc);

net/vhost-user.c

@@ -32,7 +32,7 @@ typedef struct NetVhostUserState {
     bool started;
 } NetVhostUserState;
 
-VHostNetState *vhost_user_get_vhost_net(NetClientState *nc)
+static struct vhost_net *vhost_user_get_vhost_net(NetClientState *nc)
 {
     NetVhostUserState *s = DO_UPCAST(NetVhostUserState, nc, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_USER);
@@ -231,6 +231,7 @@ static NetClientInfo net_vhost_user_info = {
         .set_vnet_be = vhost_user_set_vnet_endianness,
         .set_vnet_le = vhost_user_set_vnet_endianness,
         .check_peer_type = vhost_user_check_peer_type,
+        .get_vhost_net = vhost_user_get_vhost_net,
 };
 
 static gboolean net_vhost_user_watch(void *do_not_use, GIOCondition cond,

net/vhost-vdpa.c

@@ -132,7 +132,7 @@ static const uint64_t vdpa_svq_device_features =
 
 #define VHOST_VDPA_NET_CVQ_ASID 1
 
-VHostNetState *vhost_vdpa_get_vhost_net(NetClientState *nc)
+static struct vhost_net *vhost_vdpa_get_vhost_net(NetClientState *nc)
 {
     VhostVDPAState *s = DO_UPCAST(VhostVDPAState, nc, nc);
     assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
@@ -432,6 +432,7 @@ static NetClientInfo net_vhost_vdpa_info = {
         .set_vnet_le = vhost_vdpa_set_vnet_le,
         .check_peer_type = vhost_vdpa_check_peer_type,
         .set_steering_ebpf = vhost_vdpa_set_steering_ebpf,
+        .get_vhost_net = vhost_vdpa_get_vhost_net,
 };
 
 static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index,
@@ -1287,6 +1288,7 @@ static NetClientInfo net_vhost_vdpa_cvq_info = {
     .has_ufo = vhost_vdpa_has_ufo,
     .check_peer_type = vhost_vdpa_check_peer_type,
     .set_steering_ebpf = vhost_vdpa_set_steering_ebpf,
+    .get_vhost_net = vhost_vdpa_get_vhost_net,
 };
 
 /*