[PATCH] tpm: Return QMP error when TPM is disabled in build

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

When the management layer queries a binary built using --disable-tpm
for TPM devices, it gets confused by getting empty responses:

  { "execute": "query-tpm" }
  {
      "return": [
      ]
  }
  { "execute": "query-tpm-types" }
  {
      "return": [
      ]
  }
  { "execute": "query-tpm-models" }
  {
      "return": [
      ]
  }

Make it clearer by returning an error, mentioning the feature is
disabled:

  { "execute": "query-tpm" }
  {
      "error": {
          "class": "GenericError",
          "desc": "this feature or command is not currently supported"
      }
  }

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 stubs/tpm.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/stubs/tpm.c b/stubs/tpm.c
index 9bded191d9d..8c904215b39 100644
--- a/stubs/tpm.c
+++ b/stubs/tpm.c
@@ -7,6 +7,8 @@
 
 #include "qemu/osdep.h"
 #include "qapi/qapi-commands-tpm.h"
+#include "qapi/qmp/qerror.h"
+#include "qapi/error.h"
 #include "sysemu/tpm.h"
 #include "hw/acpi/tpm.h"
 
@@ -21,16 +23,19 @@ void tpm_cleanup(void)
 
 TPMInfoList *qmp_query_tpm(Error **errp)
 {
+    error_setg(errp, QERR_UNSUPPORTED);
     return NULL;
 }
 
 TpmTypeList *qmp_query_tpm_types(Error **errp)
 {
+    error_setg(errp, QERR_UNSUPPORTED);
     return NULL;
 }
 
 TpmModelList *qmp_query_tpm_models(Error **errp)
 {
+    error_setg(errp, QERR_UNSUPPORTED);
     return NULL;
 }
 
-- 
2.31.1