Re: [RFC PATCH v2 03/11] system/vl: Filter machine list available for a particular target binary

[Philippe Mathieu-Daudé]

On 18/4/25 05:06, Pierrick Bouvier wrote:

On 4/17/25 17:50, Philippe Mathieu-Daudé wrote:

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

Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
  include/qemu/target_info-impl.h |  3 +++
  include/qemu/target_info.h      |  8 ++++++++
  system/vl.c                     | 14 ++++++++++++++
  target_info.c                   |  5 +++++
  4 files changed, 30 insertions(+)

diff --git a/include/qemu/target_info-impl.h b/include/qemu/ target_info-impl.h

index d5c94ed5296..990fb067d20 100644
--- a/include/qemu/target_info-impl.h
+++ b/include/qemu/target_info-impl.h
@@ -16,6 +16,9 @@ typedef struct TargetInfo {
      /* runtime equivalent of TARGET_NAME definition */
      const char *const name;
+    /* QOM typename machines for this binary must implement */
+    const char *const machine_typename;
+
  } TargetInfo;
  const TargetInfo *target_info(void);
diff --git a/include/qemu/target_info.h b/include/qemu/target_info.h
index 3f6cbbbd300..e9fd2fdd7b0 100644
--- a/include/qemu/target_info.h
+++ b/include/qemu/target_info.h
@@ -16,4 +16,12 @@
   */
  const char *target_name(void);
+/**
+ * target_machine_interface_typename:
+ *
+ * Returns: Name of the QOM interface implemented by machines
+ *          usable on this target binary.
+ */
+const char *target_machine_interface_typename(void);
+
  #endif
diff --git a/system/vl.c b/system/vl.c
index d8a0fe713c9..4e43e55afe7 100644
--- a/system/vl.c
+++ b/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"

@@ -836,11 +837,17 @@ static bool usb_parse(const char *cmdline, Error **errp)

  static MachineClass *find_machine(const char *name, GSList *machines)
  {
      GSList *el;

+    const char *qom_typename_filter = target_machine_interface_typename();

      for (el = machines; el; el = el->next) {
          MachineClass *mc = el->data;
          if (!strcmp(mc->name, name) || !g_strcmp0(mc->alias, name)) {
+            if (qom_typename_filter

+                && !object_class_dynamic_cast(el->data, qom_typename_filter)) {

+                /* Machine is not for this binary: fail */
+                return NULL;
+            }
              return mc;
          }
      }
@@ -1563,6 +1570,7 @@ static void machine_help_func(const QDict *qdict)
      g_autoptr(GSList) machines = NULL;
      GSList *el;
      const char *type = qdict_get_try_str(qdict, "type");

+    const char *qom_typename_filter = target_machine_interface_typename();

      machines = object_class_get_list(TYPE_MACHINE, false);

We can replace change to system/vl.c with:

const char *machine_type = target_machine_interface_typename();
machines = object_class_get_list(machine_type, false);

Clever!

      if (type) {
@@ -1577,6 +1585,12 @@ static void machine_help_func(const QDict *qdict)
      machines = g_slist_sort(machines, machine_class_cmp);
      for (el = machines; el; el = el->next) {
          MachineClass *mc = el->data;
+
+        if (qom_typename_filter

+            && !object_class_dynamic_cast(el->data, qom_typename_filter)) {

+            /* Machine is not for this binary: skip */
+            continue;
+        }
          if (mc->alias) {

              printf("%-20s %s (alias of %s)\n", mc->alias, mc->desc, mc->name);

          }
diff --git a/target_info.c b/target_info.c
index 877a6a15014..226eed1fd7d 100644
--- a/target_info.c
+++ b/target_info.c
@@ -14,3 +14,8 @@ const char *target_name(void)
  {
      return target_info()->name;
  }
+
+const char *target_machine_interface_typename(void)
+{
+    return target_info()->machine_typename;

And here:

const char *machine_type = target_info()->machine_typename;
if (!machine_type) {
     machine_type = TYPE_MACHINE;
}
return machine_type;

+}

This way, there is no special case to handle anywhere, and we can safely replace occurrences of TYPE_MACHINE queries with target_machine_interface_typename().

As well, just a nit, but it's not important to know it's an interface, I would prefer a simpler name: target_machine_type();