net: Improve the warnings for dubious command line option combinations

Improve the warnings we give if the user specified a combination of -net
options which don't make much sense:
 * Don't warn about anything if the config is the implicit default
   "-net user -net nic" rather than one specified by the user (this will
   only kick in for boards with no NIC or if CONFIG_SLIRP is not set)
 * Diagnose the case where the user asked for NICs which the board
   didn't instantiate (for example where the user asked for two NICs
   but the board only supports one)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 31 insertions, 0 deletions

diff --git a/net.c b/net.c
index b2dfaa808..8d6a55537 100644
--- a/net.c
+++ b/net.c
@@ -1305,6 +1305,22 @@ void net_check_clients(void)
 {
     VLANState *vlan;
     VLANClientState *vc;
+    int seen_nics = 0;
+
+    /* Don't warn about the default network setup that you get if
+     * no command line -net options are specified. There are two
+     * cases that we would otherwise complain about:
+     * (1) board doesn't support a NIC but the implicit "-net nic"
+     * requested one; we'd otherwise complain about more NICs being
+     * specified than we support, and also that the vlan set up by
+     * the implicit "-net user" didn't have any NICs connected to it
+     * (2) CONFIG_SLIRP not set: we'd otherwise complain about the
+     * implicit "-net nic" setting up a nic that wasn't connected to
+     * anything.
+     */
+    if (default_net) {
+        return;
+    }
 
     QTAILQ_FOREACH(vlan, &vlans, next) {
         int has_nic = 0, has_host_dev = 0;
@@ -1312,6 +1328,7 @@ void net_check_clients(void)
         QTAILQ_FOREACH(vc, &vlan->clients, next) {
             switch (vc->info->type) {
             case NET_CLIENT_TYPE_NIC:
+                seen_nics++;
                 has_nic = 1;
                 break;
             case NET_CLIENT_TYPE_SLIRP:
@@ -1331,12 +1348,26 @@ void net_check_clients(void)
                     vlan->id);
     }
     QTAILQ_FOREACH(vc, &non_vlan_clients, next) {
+        if (vc->info->type == NET_CLIENT_TYPE_NIC) {
+            seen_nics++;
+        }
         if (!vc->peer) {
             fprintf(stderr, "Warning: %s %s has no peer\n",
                     vc->info->type == NET_CLIENT_TYPE_NIC ? "nic" : "netdev",
                     vc->name);
         }
     }
+    if (seen_nics != nb_nics) {
+        /* Number of NICs requested by user on command line doesn't match
+         * the number the model actually registered with us.
+         * This will generally only happen for models of embedded boards
+         * with no PCI bus or similar. PCI based machines can instantiate
+         * all requested NICs as PCI devices but usually embedded boards
+         * only have a single NIC.
+         */
+        fprintf(stderr, "Warning: more nics requested than this machine "
+                "supports; some have been ignored\n");
+    }
 }
 
 static int net_init_client(QemuOpts *opts, void *dummy)