core/machine: Make create_default_memdev machine a virtual method

This is in preparation for the next commit where the nitro-enclave
machine type will need to instead use a memfd backend, for the built-in
vhost-user-vsock device to work.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
Link: https://lore.kernel.org/r/20241008211727.49088-5-dorjoychy111@gmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

backends/hostmem-memfd.c

@@ -18,8 +18,6 @@
 #include "qapi/error.h"
 #include "qom/object.h"
 
-#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
-
 OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendMemfd, MEMORY_BACKEND_MEMFD)
 
 

hw/core/machine.c

@@ -1001,6 +1001,39 @@ void machine_add_audiodev_property(MachineClass *mc)
                                           "Audiodev to use for default machine devices");
 }
 
+static bool create_default_memdev(MachineState *ms, const char *path,
+                                  Error **errp)
+{
+    Object *obj;
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+    bool r = false;
+
+    obj = object_new(path ? TYPE_MEMORY_BACKEND_FILE : TYPE_MEMORY_BACKEND_RAM);
+    if (path) {
+        if (!object_property_set_str(obj, "mem-path", path, errp)) {
+            goto out;
+        }
+    }
+    if (!object_property_set_int(obj, "size", ms->ram_size, errp)) {
+        goto out;
+    }
+    object_property_add_child(object_get_objects_root(), mc->default_ram_id,
+                              obj);
+    /* Ensure backend's memory region name is equal to mc->default_ram_id */
+    if (!object_property_set_bool(obj, "x-use-canonical-path-for-ramblock-id",
+                             false, errp)) {
+        goto out;
+    }
+    if (!user_creatable_complete(USER_CREATABLE(obj), errp)) {
+        goto out;
+    }
+    r = object_property_set_link(OBJECT(ms), "memory-backend", obj, errp);
+
+out:
+    object_unref(obj);
+    return r;
+}
+
 static void machine_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
@@ -1020,6 +1053,8 @@ static void machine_class_init(ObjectClass *oc, void *data)
      */
     mc->numa_mem_align_shift = 23;
 
+    mc->create_default_memdev = create_default_memdev;
+
     object_class_property_add_str(oc, "kernel",
         machine_get_kernel, machine_set_kernel);
     object_class_property_set_description(oc, "kernel",
@@ -1413,38 +1448,6 @@ MemoryRegion *machine_consume_memdev(MachineState *machine,
     return ret;
 }
 
-static bool create_default_memdev(MachineState *ms, const char *path, Error **errp)
-{
-    Object *obj;
-    MachineClass *mc = MACHINE_GET_CLASS(ms);
-    bool r = false;
-
-    obj = object_new(path ? TYPE_MEMORY_BACKEND_FILE : TYPE_MEMORY_BACKEND_RAM);
-    if (path) {
-        if (!object_property_set_str(obj, "mem-path", path, errp)) {
-            goto out;
-        }
-    }
-    if (!object_property_set_int(obj, "size", ms->ram_size, errp)) {
-        goto out;
-    }
-    object_property_add_child(object_get_objects_root(), mc->default_ram_id,
-                              obj);
-    /* Ensure backend's memory region name is equal to mc->default_ram_id */
-    if (!object_property_set_bool(obj, "x-use-canonical-path-for-ramblock-id",
-                             false, errp)) {
-        goto out;
-    }
-    if (!user_creatable_complete(USER_CREATABLE(obj), errp)) {
-        goto out;
-    }
-    r = object_property_set_link(OBJECT(ms), "memory-backend", obj, errp);
-
-out:
-    object_unref(obj);
-    return r;
-}
-
 const char *machine_class_default_cpu_type(MachineClass *mc)
 {
     if (mc->valid_cpu_types && !mc->valid_cpu_types[1]) {
@@ -1548,7 +1551,9 @@ void machine_run_board_init(MachineState *machine, const char *mem_path, Error *
                 machine_class->default_ram_id);
             return;
         }
-        if (!create_default_memdev(current_machine, mem_path, errp)) {
+
+        if (!machine_class->create_default_memdev(current_machine, mem_path,
+                                                  errp)) {
             return;
         }
     }

include/hw/boards.h

@@ -314,6 +314,8 @@ struct MachineClass {
     int64_t (*get_default_cpu_node_id)(const MachineState *ms, int idx);
     ram_addr_t (*fixup_ram_size)(ram_addr_t size);
     uint64_t smbios_memory_device_size;
+    bool (*create_default_memdev)(MachineState *ms, const char *path,
+                                  Error **errp);
 };
 
 /**

include/sysemu/hostmem.h

@@ -39,6 +39,8 @@ OBJECT_DECLARE_TYPE(HostMemoryBackend, HostMemoryBackendClass,
  */
 #define TYPE_MEMORY_BACKEND_FILE "memory-backend-file"
 
+#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
+
 
 /**
  * HostMemoryBackendClass: