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>

1 files changed, 13 insertions, 7 deletions

diff --git a/net/tap.c b/net/tap.c
index ae1c7e3983..4beba6d7a7 100644
--- a/net/tap.c
+++ b/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);