net: Add a new convenience option "--nic" to configure default/on-board NICs

The legacy "-net" option can be quite confusing for the users since most
people do not expect to get a "vlan" hub between their emulated guest
hardware and the host backend. But so far, we are also not able to get
rid of "-net" completely, since it is the only way to configure on-board
NICs that can not be instantiated via "-device" yet. It's also a little
bit shorter to type "-net nic -net tap" instead of "-device xyz,netdev=n1
-netdev tap,id=n1".

So what we need is a new convenience option that is shorter to type than
the full -device + -netdev stuff, and which can be used to configure the
on-board NICs that can not be handled via -device yet. Thus this patch now
provides such a new option "--nic": It adds an entry in the nd_table to
configure a on-board / default NIC, creates a host backend and connects
the two directly, without a confusing "vlan" hub inbetween.

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

net/net.c

@@ -1462,6 +1462,67 @@ static int net_init_netdev(void *dummy, QemuOpts *opts, Error **errp)
     return net_client_init(opts, true, errp);
 }
 
+/* For the convenience "--nic" parameter */
+static int net_param_nic(void *dummy, QemuOpts *opts, Error **errp)
+{
+    char *mac, *nd_id;
+    int idx, ret;
+    NICInfo *ni;
+    const char *type;
+
+    type = qemu_opt_get(opts, "type");
+    if (type && g_str_equal(type, "none")) {
+        return 0;    /* Nothing to do, default_net is cleared in vl.c */
+    }
+
+    idx = nic_get_free_idx();
+    if (idx == -1 || nb_nics >= MAX_NICS) {
+        error_setg(errp, "no more on-board/default NIC slots available");
+        return -1;
+    }
+
+    if (!type) {
+        qemu_opt_set(opts, "type", "user", &error_abort);
+    }
+
+    ni = &nd_table[idx];
+    memset(ni, 0, sizeof(*ni));
+    ni->model = qemu_opt_get_del(opts, "model");
+
+    /* Create an ID if the user did not specify one */
+    nd_id = g_strdup(qemu_opts_id(opts));
+    if (!nd_id) {
+        nd_id = g_strdup_printf("__org.qemu.nic%i\n", idx);
+        qemu_opts_set_id(opts, nd_id);
+    }
+
+    /* Handle MAC address */
+    mac = qemu_opt_get_del(opts, "mac");
+    if (mac) {
+        ret = net_parse_macaddr(ni->macaddr.a, mac);
+        g_free(mac);
+        if (ret) {
+            error_setg(errp, "invalid syntax for ethernet address");
+            return -1;
+        }
+        if (is_multicast_ether_addr(ni->macaddr.a)) {
+            error_setg(errp, "NIC cannot have multicast MAC address");
+            return -1;
+        }
+    }
+    qemu_macaddr_default_if_unset(&ni->macaddr);
+
+    ret = net_client_init(opts, true, errp);
+    if (ret == 0) {
+        ni->netdev = qemu_find_netdev(nd_id);
+        ni->used = true;
+        nb_nics++;
+    }
+
+    g_free(nd_id);
+    return ret;
+}
+
 int net_init_clients(Error **errp)
 {
     net_change_state_entry =
@@ -1474,6 +1535,10 @@ int net_init_clients(Error **errp)
         return -1;
     }
 
+    if (qemu_opts_foreach(qemu_find_opts("nic"), net_param_nic, NULL, errp)) {
+        return -1;
+    }
+
     if (qemu_opts_foreach(qemu_find_opts("net"), net_init_client, NULL, errp)) {
         return -1;
     }
@@ -1549,6 +1614,19 @@ QemuOptsList qemu_netdev_opts = {
     },
 };
 
+QemuOptsList qemu_nic_opts = {
+    .name = "nic",
+    .implied_opt_name = "type",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_nic_opts.head),
+    .desc = {
+        /*
+         * no elements => accept any params
+         * validation will happen later
+         */
+        { /* end of list */ }
+    },
+};
+
 QemuOptsList qemu_net_opts = {
     .name = "net",
     .implied_opt_name = "type",