[PATCH 2/2] qom: Improve error message in module_object_class_by_name()

["Jose R. Ziviani" <jziviani@suse.de>]

module_object_class_by_name() calls module_load_qom_one if the object
is provided by a dynamically linked library. Such library might not be
available at this moment - for instance, it can be a package not yet
installed. Thus, instead of assert error messages, this patch outputs
more friendly messages.

Current error messages:
$ ./qemu-system-x86_64 -machine q35 -accel tcg -kernel /boot/vmlinuz
...
ERROR:../accel/accel-softmmu.c:82:accel_init_ops_interfaces: assertion failed: (ops != NULL)
Bail out! ERROR:../accel/accel-softmmu.c:82:accel_init_ops_interfaces: assertion failed: (ops != NULL)
[1]    31964 IOT instruction (core dumped)  ./qemu-system-x86_64 ...

New error message:
$ ./qemu-system-x86_64 -machine q35 -accel tcg -kernel /boot/vmlinuz
accel-tcg-x86_64 module is missing, install the package or config the library path correctly.

Or with other modules, when possible:
$ ./qemu-system-x86_64 -machine q35 -accel kvm -kernel /boot/vmlinuz -vga qxl                                                                     ✹
hw-display-qxl module is missing, install the package or config the library path correctly.
qemu-system-x86_64: QXL VGA not available

$ make check
...
Running test qtest-x86_64/test-filter-mirror
Running test qtest-x86_64/endianness-test
accel-qtest-x86_64 module is missing, install the package or config the library path correctly.
accel-qtest-x86_64 module is missing, install the package or config the library path correctly.
accel-qtest-x86_64 module is missing, install the package or config the library path correctly.
accel-qtest-x86_64 module is missing, install the package or config the library path correctly.
accel-qtest-x86_64 module is missing, install the package or config the library path correctly.
accel-tcg-x86_64 module is missing, install the package or config the library path correctly.
...

Signed-off-by: Jose R. Ziviani <jziviani@suse.de>
---
 accel/accel-softmmu.c | 5 ++++-
 qom/object.c          | 9 +++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/accel/accel-softmmu.c b/accel/accel-softmmu.c
index 67276e4f52..52449ac2d0 100644
--- a/accel/accel-softmmu.c
+++ b/accel/accel-softmmu.c
@@ -79,7 +79,10 @@ void accel_init_ops_interfaces(AccelClass *ac)
      * all accelerators need to define ops, providing at least a mandatory
      * non-NULL create_vcpu_thread operation.
      */
-    g_assert(ops != NULL);
+    if (ops == NULL) {
+        exit(1);
+    }
+
     if (ops->ops_init) {
         ops->ops_init(ops);
     }
diff --git a/qom/object.c b/qom/object.c
index 6a01d56546..3a170ea9df 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -10,6 +10,7 @@
  * See the COPYING file in the top-level directory.
  */
 
+#include "qemu/module.h"
 #include "qemu/osdep.h"
 #include "hw/qdev-core.h"
 #include "qapi/error.h"
@@ -1031,8 +1032,16 @@ ObjectClass *module_object_class_by_name(const char *typename)
     oc = object_class_by_name(typename);
 #ifdef CONFIG_MODULES
     if (!oc) {
+        const char *module_name = module_get_name_from_obj(typename);
         module_load_qom_one(typename);
         oc = object_class_by_name(typename);
+        if (!oc && module_name) {
+            if (!module_is_loaded(module_name)) {
+                fprintf(stderr, "%s module is missing, install the "
+                                "package or config the library path "
+                                "correctly.\n", module_name);
+            }
+        }
     }
 #endif
     return oc;
-- 
2.32.0