system/vl: Filter machine list available for a particular target binary

Binaries can register a QOM type to filter their machines
by filling their TargetInfo::machine_typename field.

This can be used by example by main() -> machine_help_func()
to filter the machines list.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

include/qemu/target-info-impl.h

@@ -14,6 +14,8 @@
 typedef struct TargetInfo {
     /* runtime equivalent of TARGET_NAME definition */
     const char *target_name;
+    /* QOM typename machines for this binary must implement */
+    const char *machine_typename;
 } TargetInfo;
 
 /**

include/qemu/target-info.h

@@ -16,6 +16,14 @@
  */
 const char *target_name(void);
 
+/**
+ * target_machine_typename:
+ *
+ * Returns: Name of the QOM interface implemented by machines
+ *          usable on this target binary.
+ */
+const char *target_machine_typename(void);
+
 /**
  * target_cpu_type:
  *

system/vl.c

@@ -27,6 +27,7 @@
 #include "qemu/datadir.h"
 #include "qemu/units.h"
 #include "qemu/module.h"
+#include "qemu/target-info.h"
 #include "exec/cpu-common.h"
 #include "exec/page-vary.h"
 #include "hw/qdev-properties.h"
@@ -1564,7 +1565,7 @@ static void machine_help_func(const QDict *qdict)
     GSList *el;
     const char *type = qdict_get_try_str(qdict, "type");
 
-    machines = object_class_get_list(TYPE_MACHINE, false);
+    machines = object_class_get_list(target_machine_typename(), false);
     if (type) {
         ObjectClass *machine_class = OBJECT_CLASS(find_machine(type, machines));
         if (machine_class) {

target-info-stub.c

@@ -9,10 +9,12 @@
 #include "qemu/osdep.h"
 #include "qemu/target-info.h"
 #include "qemu/target-info-impl.h"
+#include "hw/boards.h"
 #include "cpu.h"
 
 static const TargetInfo target_info_stub = {
     .target_name = TARGET_NAME,
+    .machine_typename = TYPE_MACHINE,
 };
 
 const TargetInfo *target_info(void)

target-info.c

@@ -14,3 +14,8 @@ const char *target_name(void)
 {
     return target_info()->target_name;
 }
+
+const char *target_machine_typename(void)
+{
+    return target_info()->machine_typename;
+}