pvpanic: Emit GUEST_PVSHUTDOWN QMP event on pvpanic shutdown signal

Emit a QMP event on receiving a PVPANIC_SHUTDOWN event. Even though a typical
SHUTDOWN event will be sent, it will be indistinguishable from a shutdown
originating from other cases (e.g. KVM exit due to KVM_SYSTEM_EVENT_SHUTDOWN)
that also issue the guest-shutdown cause.
A management layer application can detect the new GUEST_PVSHUTDOWN event to
determine if the guest is using the pvpanic interface to request shutdowns.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Message-Id: <20240527-pvpanic-shutdown-v8-6-5a28ec02558b@t-8ch.de>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

qapi/run-state.json

@@ -462,6 +462,20 @@
 { 'event': 'GUEST_CRASHLOADED',
   'data': { 'action': 'GuestPanicAction', '*info': 'GuestPanicInformation' } }
 
+##
+# @GUEST_PVSHUTDOWN:
+#
+# Emitted when guest submits a shutdown request via pvpanic interface
+#
+# Since: 9.1
+#
+# Example:
+#
+#     <- { "event": "GUEST_PVSHUTDOWN",
+#          "timestamp": { "seconds": 1648245259, "microseconds": 893771 } }
+##
+{ 'event': 'GUEST_PVSHUTDOWN' }
+
 ##
 # @GuestPanicAction:
 #

system/runstate.c

@@ -586,6 +586,7 @@ void qemu_system_guest_crashloaded(GuestPanicInformation *info)
 
 void qemu_system_guest_pvshutdown(void)
 {
+    qapi_event_send_guest_pvshutdown();
     qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN);
 }