network: improve error report when firewall chain creation fails

During startup we create some top level chains in which all
virtual network firewall rules will be placed. The upfront
creation is done to avoid slowing down creation of individual
virtual networks by checking for chain existance every time.

There are some factors which can cause this upfront creation
to fail and while a message will get into the libvirtd log
this won't be seen by users who later try to start a virtual
network. Instead they'll just get a message saying that the
libvirt top level chain does not exist. This message is
accurate, but unhelpful for solving the root cause.

This patch thus saves any error during daemon startup and
reports it when trying to create a virtual network later.

Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/network/bridge_driver.c

@@ -2095,8 +2095,7 @@ static void
 networkReloadFirewallRules(virNetworkDriverStatePtr driver, bool startup)
 {
     VIR_INFO("Reloading iptables rules");
-    if (networkPreReloadFirewallRules(startup) < 0)
-        return;
+    networkPreReloadFirewallRules(startup);
     virNetworkObjListForEach(driver->networks,
                              networkReloadFirewallRulesHelper,
                              NULL);

src/network/bridge_driver_linux.c

@@ -35,11 +35,25 @@ VIR_LOG_INIT("network.bridge_driver_linux");
 
 #define PROC_NET_ROUTE "/proc/net/route"
 
-int networkPreReloadFirewallRules(bool startup)
+static virErrorPtr errInit;
+
+void networkPreReloadFirewallRules(bool startup)
 {
-    int ret = iptablesSetupPrivateChains();
-    if (ret < 0)
-        return -1;
+    int rc;
+
+    /* We create global rules upfront as we don't want
+     * the perf hit of conditionally figuring out whether
+     * to create them each time a network is started.
+     *
+     * Any errors here are saved to be reported at time
+     * of starting the network though as that makes them
+     * more likely to be seen by a human
+     */
+    rc = iptablesSetupPrivateChains();
+    if (rc < 0) {
+        errInit = virSaveLastError();
+        virResetLastError();
+    }
 
     /*
      * If this is initial startup, and we just created the
@@ -54,10 +68,8 @@ int networkPreReloadFirewallRules(bool startup)
      * rules will be present. Thus we can safely just tell it
      * to always delete from the builin chain
      */
-    if (startup && ret == 1)
+    if (startup && rc == 1)
         iptablesSetDeletePrivate(false);
-
-    return 0;
 }
 
 
@@ -671,6 +683,11 @@ int networkAddFirewallRules(virNetworkDefPtr def)
     virFirewallPtr fw = NULL;
     int ret = -1;
 
+    if (errInit) {
+        virSetError(errInit);
+        return -1;
+    }
+
     if (def->bridgeZone) {
 
         /* if a firewalld zone has been specified, fail/log an error

src/network/bridge_driver_nop.c

@@ -19,9 +19,8 @@
 
 #include <config.h>
 
-int networkPreReloadFirewallRules(bool startup ATTRIBUTE_UNUSED)
+void networkPreReloadFirewallRules(bool startup ATTRIBUTE_UNUSED)
 {
-    return 0;
 }
 
 

src/network/bridge_driver_platform.h

@@ -58,7 +58,7 @@ struct _virNetworkDriverState {
 typedef struct _virNetworkDriverState virNetworkDriverState;
 typedef virNetworkDriverState *virNetworkDriverStatePtr;
 
-int networkPreReloadFirewallRules(bool startup);
+void networkPreReloadFirewallRules(bool startup);
 void networkPostReloadFirewallRules(bool startup);
 
 int networkCheckRouteCollision(virNetworkDefPtr def);