qga: return a more explicit error on why a command is disabled

qmp_disable_command() now takes an optional error string to return a
more explicit error message.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1928806

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
*fix up 80+ char line
Signed-off-by: Michael Roth <michael.roth@amd.com>

include/qapi/qmp/dispatch.h

@@ -36,6 +36,7 @@ typedef struct QmpCommand
     QmpCommandOptions options;
     QTAILQ_ENTRY(QmpCommand) node;
     bool enabled;
+    const char *disable_reason;
 } QmpCommand;
 
 typedef QTAILQ_HEAD(QmpCommandList, QmpCommand) QmpCommandList;
@@ -44,7 +45,8 @@ void qmp_register_command(QmpCommandList *cmds, const char *name,
                           QmpCommandFunc *fn, QmpCommandOptions options);
 const QmpCommand *qmp_find_command(const QmpCommandList *cmds,
                                    const char *name);
-void qmp_disable_command(QmpCommandList *cmds, const char *name);
+void qmp_disable_command(QmpCommandList *cmds, const char *name,
+                         const char *err_msg);
 void qmp_enable_command(QmpCommandList *cmds, const char *name);
 
 bool qmp_command_is_enabled(const QmpCommand *cmd);

qapi/qmp-dispatch.c

@@ -157,8 +157,10 @@ QDict *qmp_dispatch(const QmpCommandList *cmds, QObject *request,
     }
     if (!cmd->enabled) {
         error_set(&err, ERROR_CLASS_COMMAND_NOT_FOUND,
-                  "The command %s has been disabled for this instance",
-                  command);
+                  "Command %s has been disabled%s%s",
+                  command,
+                  cmd->disable_reason ? ": " : "",
+                  cmd->disable_reason ?: "");
         goto out;
     }
     if (oob && !(cmd->options & QCO_ALLOW_OOB)) {

qapi/qmp-registry.c

@@ -43,26 +43,28 @@ const QmpCommand *qmp_find_command(const QmpCommandList *cmds, const char *name)
 }
 
 static void qmp_toggle_command(QmpCommandList *cmds, const char *name,
-                               bool enabled)
+                               bool enabled, const char *disable_reason)
 {
     QmpCommand *cmd;
 
     QTAILQ_FOREACH(cmd, cmds, node) {
         if (strcmp(cmd->name, name) == 0) {
             cmd->enabled = enabled;
+            cmd->disable_reason = disable_reason;
             return;
         }
     }
 }
 
-void qmp_disable_command(QmpCommandList *cmds, const char *name)
+void qmp_disable_command(QmpCommandList *cmds, const char *name,
+                         const char *disable_reason)
 {
-    qmp_toggle_command(cmds, name, false);
+    qmp_toggle_command(cmds, name, false, disable_reason);
 }
 
 void qmp_enable_command(QmpCommandList *cmds, const char *name)
 {
-    qmp_toggle_command(cmds, name, true);
+    qmp_toggle_command(cmds, name, true, NULL);
 }
 
 bool qmp_command_is_enabled(const QmpCommand *cmd)

qga/main.c

@@ -375,7 +375,7 @@ static void ga_disable_non_whitelisted(const QmpCommand *cmd, void *opaque)
     }
     if (!whitelisted) {
         g_debug("disabling command: %s", name);
-        qmp_disable_command(&ga_commands, name);
+        qmp_disable_command(&ga_commands, name, "the agent is in frozen state");
     }
 }
 
@@ -1328,7 +1328,7 @@ static GAState *initialize_agent(GAConfig *config, int socket_activation)
         s->blacklist = config->blacklist;
         do {
             g_debug("disabling command: %s", (char *)l->data);
-            qmp_disable_command(&ga_commands, l->data);
+            qmp_disable_command(&ga_commands, l->data, NULL);
             l = g_list_next(l);
         } while (l);
     }