net: Track netdevs in NetClientState rather than QemuOpt

As mentioned in the previous patch, our use of QemuOpt group "netdev"
has two purposes: collect the CLI arguments, and serve as a witness
for monitor hotplug actions.  As the latter didn't use anything but an
id, it felt rather unclean to have to touch QemuOpts at all when going
through QMP, so let's instead track things with a bool field in
NetClientState.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200317201711.322764-3-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

include/net/net.h

@@ -98,6 +98,7 @@ struct NetClientState {
     unsigned rxfilter_notify_enabled:1;
     int vring_enable;
     int vnet_hdr_len;
+    bool is_netdev;
     QTAILQ_HEAD(, NetFilterState) filters;
 };
 

monitor/misc.c

@@ -2035,13 +2035,11 @@ void netdev_del_completion(ReadLineState *rs, int nb_args, const char *str)
     count = qemu_find_net_clients_except(NULL, ncs, NET_CLIENT_DRIVER_NIC,
                                          MAX_QUEUE_NUM);
     for (i = 0; i < MIN(count, MAX_QUEUE_NUM); i++) {
-        QemuOpts *opts;
         const char *name = ncs[i]->name;
         if (strncmp(str, name, len)) {
             continue;
         }
-        opts = qemu_opts_find(qemu_find_opts_err("netdev", NULL), name);
-        if (opts) {
+        if (ncs[i]->is_netdev) {
             readline_add_completion(rs, name);
         }
     }

net/net.c

@@ -1060,6 +1060,15 @@ static int net_client_init1(const void *object, bool is_netdev, Error **errp)
         }
         return -1;
     }
+
+    if (is_netdev) {
+        NetClientState *nc;
+
+        nc = qemu_find_netdev(netdev->id);
+        assert(nc);
+        nc->is_netdev = true;
+    }
+
     return 0;
 }
 
@@ -1172,34 +1181,12 @@ void netdev_add(QemuOpts *opts, Error **errp)
 
 void qmp_netdev_add(Netdev *netdev, Error **errp)
 {
-    Error *local_err = NULL;
-    QemuOptsList *opts_list;
-    QemuOpts *opts;
-
-    opts_list = qemu_find_opts_err("netdev", &local_err);
-    if (local_err) {
-        goto out;
-    }
-
-    opts = qemu_opts_create(opts_list, netdev->id, 1, &local_err);
-    if (local_err) {
-        goto out;
-    }
-
-    net_client_init1(netdev, true, &local_err);
-    if (local_err) {
-        qemu_opts_del(opts);
-        goto out;
-    }
-
-out:
-    error_propagate(errp, local_err);
+    net_client_init1(netdev, true, errp);
 }
 
 void qmp_netdev_del(const char *id, Error **errp)
 {
     NetClientState *nc;
-    QemuOpts *opts;
 
     nc = qemu_find_netdev(id);
     if (!nc) {
@@ -1208,14 +1195,12 @@ void qmp_netdev_del(const char *id, Error **errp)
         return;
     }
 
-    opts = qemu_opts_find(qemu_find_opts_err("netdev", NULL), id);
-    if (!opts) {
+    if (!nc->is_netdev) {
         error_setg(errp, "Device '%s' is not a netdev", id);
         return;
     }
 
     qemu_del_net_client(nc);
-    qemu_opts_del(opts);
 }
 
 static void netfilter_print_info(Monitor *mon, NetFilterState *nf)