net: List available netdevs with "-netdev help"

Other options like "-chardev" or "-device" feature a nice help text
with the available devices when being called with "help" or "?".
Since it is quite useful, especially if you want to see which network
backends have been compiled into the QEMU binary, let's provide such
a help text for "-netdev", too.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

diff --git a/net/net.c b/net/net.c
index e213a619754a47e8db29c649a4fc89f34315275f..cf07e15cd467d645b96b5625eac23a898c694011 100644 (file)
--- a/net/net.c
+++ b/net/net.c
@@ -1086,6 +1086,38 @@ static int net_client_init1(const void *object, bool is_netdev, Error **errp)
     return 0;
 }
 
+static void show_netdevs(void)
+{
+    int idx;
+    const char *available_netdevs[] = {
+        "socket",
+        "hubport",
+        "tap",
+#ifdef CONFIG_SLIRP
+        "user",
+#endif
+#ifdef CONFIG_L2TPV3
+        "l2tpv3",
+#endif
+#ifdef CONFIG_VDE
+        "vde",
+#endif
+#ifdef CONFIG_NET_BRIDGE
+        "bridge",
+#endif
+#ifdef CONFIG_NETMAP
+        "netmap",
+#endif
+#ifdef CONFIG_POSIX
+        "vhost-user",
+#endif
+    };
+
+    printf("Available netdev backend types:\n");
+    for (idx = 0; idx < ARRAY_SIZE(available_netdevs); idx++) {
+        puts(available_netdevs[idx]);
+    }
+}
 
 int net_client_init(QemuOpts *opts, bool is_netdev, Error **errp)
 {
@@ -1094,7 +1126,10 @@ int net_client_init(QemuOpts *opts, bool is_netdev, Error **errp)
     int ret = -1;
     Visitor *v = opts_visitor_new(opts);
 
-    {
+    if (is_netdev && is_help_option(qemu_opt_get(opts, "type"))) {
+        show_netdevs();
+        exit(0);
+    } else {
         /* Parse convenience option format ip6-net=fec0::0[/64] */
         const char *ip6_net = qemu_opt_get(opts, "ipv6-net");