Monitor/QMP: Don't allow cont on bad VM state

We have two states where issuing cont before system_reset can
cause problems: RSTATE_SHUTDOWN (when -no-shutdown is used) and
RSTATE_PANICKED (which only happens with kvm).

This commit fixes that by doing the following when state is
RSTATE_SHUTDOWN or RSTATE_PANICKED:

 1. returning an error to the user/client if cont is issued
 2. automatically transition to RSTATE_PAUSED during system_reset

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

monitor.c

@@ -1314,7 +1314,12 @@ static int do_cont(Monitor *mon, const QDict *qdict, QObject **ret_data)
     if (runstate_check(RSTATE_IN_MIGRATE)) {
         qerror_report(QERR_MIGRATION_EXPECTED);
         return -1;
+    } else if (runstate_check(RSTATE_PANICKED) ||
+               runstate_check(RSTATE_SHUTDOWN)) {
+        qerror_report(QERR_RESET_REQUIRED);
+        return -1;
     }
+
     bdrv_iterate(encrypted_bdrv_it, &context);
     /* only resume the vm if all keys are set and valid */
     if (!context.err) {

qerror.c

@@ -193,6 +193,10 @@ static const QErrorStringTable qerror_table[] = {
         .error_fmt = QERR_QMP_EXTRA_MEMBER,
         .desc      = "QMP input object member '%(member)' is unexpected",
     },
+    {
+        .error_fmt = QERR_RESET_REQUIRED,
+        .desc      = "Resetting the Virtual Machine is required",
+    },
     {
         .error_fmt = QERR_SET_PASSWD_FAILED,
         .desc      = "Could not set password",

qerror.h

@@ -163,6 +163,9 @@ QError *qobject_to_qerror(const QObject *obj);
 #define QERR_QMP_EXTRA_MEMBER \
     "{ 'class': 'QMPExtraInputObjectMember', 'data': { 'member': %s } }"
 
+#define QERR_RESET_REQUIRED \
+    "{ 'class': 'ResetRequired', 'data': {} }"
+
 #define QERR_SET_PASSWD_FAILED \
     "{ 'class': 'SetPasswdFailed', 'data': {} }"
 

vl.c

@@ -1573,6 +1573,10 @@ static void main_loop(void)
             cpu_synchronize_all_states();
             qemu_system_reset(VMRESET_REPORT);
             resume_all_vcpus();
+            if (runstate_check(RSTATE_PANICKED) ||
+                runstate_check(RSTATE_SHUTDOWN)) {
+                runstate_set(RSTATE_PAUSED);
+            }
         }
         if (qemu_powerdown_requested()) {
             monitor_protocol_event(QEVENT_POWERDOWN, NULL);