From 1a709119c593c74fb7db745030a0dda33e7dd18c Mon Sep 17 00:00:00 2001
From: Alexander Graf <agraf@suse.de>
Date: Wed, 12 Dec 2012 19:11:31 +0100
Subject: [PATCH] net: Warn about default MAC address

[AF: Suppress for QTest]
---
 net/net.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/net/net.c b/net/net.c
index 0be084d..552e233 100644
--- a/net/net.c
+++ b/net/net.c
@@ -42,6 +42,7 @@
 #include "qapi/opts-visitor.h"
 #include "qapi/dealloc-visitor.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/qtest.h"
 
 /* Net bridge is currently not supported for W32. */
 #if !defined(_WIN32)
@@ -160,6 +161,28 @@ void qemu_format_nic_info_str(NetClientState *nc, uint8_t macaddr[6])
              macaddr[3], macaddr[4], macaddr[5]);
 }
 
+static void default_mac_check(void)
+{
+    static const MACAddr def_mac = { .a = { 0x52,0x54,0x00,0x12,0x34,0x56 } };
+    static int warned = 0;
+    int i;
+
+    for (i = 0; i < MAX_NICS; i++) {
+        if (!nd_table[i].used) {
+            continue;
+        }
+        if (memcmp(nd_table[i].macaddr.a, def_mac.a, 5)) {
+            continue;
+        }
+        if (nd_table[i].macaddr.a[5] >= 0x56 &&
+            nd_table[i].macaddr.a[5] < 0x56  + MAX_NICS && !warned && !qtest_enabled()) {
+            warned = 1;
+            fprintf(stderr, "Warning: default mac address being used, creating "
+                    "potential for address conflict\n");
+        }
+    }
+}
+
 void qemu_macaddr_default_if_unset(MACAddr *macaddr)
 {
     static int index = 0;
@@ -1313,6 +1336,7 @@ int net_init_clients(void)
     if (qemu_opts_foreach(net, net_init_client, NULL, 1) == -1) {
         return -1;
     }
+    default_mac_check();
 
     return 0;
 }