qemu: agent: Differentiate errors when the agent channel was hotplugged

When the guest agent channel gets hotplugged to a VM, libvirt would
still report that "QEMU guest agent is not configured" rather than
stating that the connection was not established yet.

Currently the code won't be able to connect to the agent after hotplug
but that will change in a later patch.

As the qemuFindAgentConfig() helper is quite helpful in this case move
it to a more usable place and export it.

src/qemu/qemu_domain.c

@@ -2975,11 +2975,19 @@ qemuDomainAgentAvailable(virDomainObjPtr vm,
         return false;
     }
     if (!priv->agent) {
-        if (reportError) {
-            virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
-                           _("QEMU guest agent is not configured"));
+        if (qemuFindAgentConfig(vm->def)) {
+            if (reportError) {
+                virReportError(VIR_ERR_AGENT_UNRESPONSIVE, "%s",
+                               _("QEMU guest agent is not connected"));
+            }
+            return false;
+        } else {
+            if (reportError) {
+                virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
+                               _("QEMU guest agent is not configured"));
+            }
+            return false;
         }
-        return false;
     }
     if (virDomainObjGetState(vm, NULL) != VIR_DOMAIN_RUNNING) {
         if (reportError) {
@@ -3077,3 +3085,32 @@ qemuDomainSupportsBlockJobs(virDomainObjPtr vm,
 
     return 0;
 }
+
+
+/**
+ * qemuFindAgentConfig:
+ * @def: domain definition
+ *
+ * Returns the pointer to the channel definition that is used to access the
+ * guest agent if the agent is configured or NULL otherwise.
+ */
+virDomainChrSourceDefPtr
+qemuFindAgentConfig(virDomainDefPtr def)
+{
+    virDomainChrSourceDefPtr config = NULL;
+    size_t i;
+
+    for (i = 0; i < def->nchannels; i++) {
+        virDomainChrDefPtr channel = def->channels[i];
+
+        if (channel->targetType != VIR_DOMAIN_CHR_CHANNEL_TARGET_TYPE_VIRTIO)
+            continue;
+
+        if (STREQ_NULLABLE(channel->target.name, "org.qemu.guest_agent.0")) {
+            config = &channel->source;
+            break;
+        }
+    }
+
+    return config;
+}

src/qemu/qemu_domain.h

@@ -439,4 +439,6 @@ bool qemuDomainDiskBlockJobIsActive(virDomainDiskDefPtr disk);
 int qemuDomainAlignMemorySizes(virDomainDefPtr def);
 void qemuDomainMemoryDeviceAlignSize(virDomainMemoryDefPtr mem);
 
+virDomainChrSourceDefPtr qemuFindAgentConfig(virDomainDefPtr def);
+
 #endif /* __QEMU_DOMAIN_H__ */

src/qemu/qemu_process.c

@@ -201,26 +201,6 @@ static qemuAgentCallbacks agentCallbacks = {
     .errorNotify = qemuProcessHandleAgentError,
 };
 
-static virDomainChrSourceDefPtr
-qemuFindAgentConfig(virDomainDefPtr def)
-{
-    virDomainChrSourceDefPtr config = NULL;
-    size_t i;
-
-    for (i = 0; i < def->nchannels; i++) {
-        virDomainChrDefPtr channel = def->channels[i];
-
-        if (channel->targetType != VIR_DOMAIN_CHR_CHANNEL_TARGET_TYPE_VIRTIO)
-            continue;
-
-        if (STREQ_NULLABLE(channel->target.name, "org.qemu.guest_agent.0")) {
-            config = &channel->source;
-            break;
-        }
-    }
-
-    return config;
-}
 
 static int
 qemuConnectAgent(virQEMUDriverPtr driver, virDomainObjPtr vm)