migration: vmsd errp handlers: return bool

No code actually depend on specific errno values returned by
vmstate_load_state. The only use of it is to check for success,
and sometimes inject numeric error values into error messages
in migration code. The latter is not a stopper for gradual
conversion to "errp + bool return value" APIs.

Big analysis of vmstate_load_state() callers, showing that
specific errno values are not actually used, is done by Peter
here:

https://lore.kernel.org/qemu-devel/aQDdRn8t0B8oE3gf@x1.local/

Converting of vmstate_load_state() itself will follow in
another series.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Link: https://lore.kernel.org/r/20251028170926.77219-2-vsementsov@yandex-team.ru
Signed-off-by: Peter Xu <peterx@redhat.com>

backends/tpm/tpm_emulator.c

@@ -962,24 +962,22 @@ static void tpm_emulator_vm_state_change(void *opaque, bool running,
 
 /*
  * Load the TPM state blobs into the TPM.
- *
- * Returns negative errno codes in case of error.
  */
-static int tpm_emulator_post_load(void *opaque, int version_id, Error **errp)
+static bool tpm_emulator_post_load(void *opaque, int version_id, Error **errp)
 {
     TPMBackend *tb = opaque;
     int ret;
 
     ret = tpm_emulator_set_state_blobs(tb, errp);
     if (ret < 0) {
-        return ret;
+        return false;
     }
 
     if (tpm_emulator_startup_tpm_resume(tb, 0, true, errp) < 0) {
-        return -EIO;
+        return false;
     }
 
-    return 0;
+    return true;
 }
 
 static const VMStateDescription vmstate_tpm_emulator = {

docs/devel/migration/main.rst

@@ -446,15 +446,15 @@ The functions to do that are inside a vmstate definition, and are called:
 
 Following are the errp variants of these functions.
 
-- ``int (*pre_load_errp)(void *opaque, Error **errp);``
+- ``bool (*pre_load_errp)(void *opaque, Error **errp);``
 
   This function is called before we load the state of one device.
 
-- ``int (*post_load_errp)(void *opaque, int version_id, Error **errp);``
+- ``bool (*post_load_errp)(void *opaque, int version_id, Error **errp);``
 
   This function is called after we load the state of one device.
 
-- ``int (*pre_save_errp)(void *opaque, Error **errp);``
+- ``bool (*pre_save_errp)(void *opaque, Error **errp);``
 
   This function is called before we save the state of one device.
 

include/migration/vmstate.h

@@ -218,11 +218,11 @@ struct VMStateDescription {
     int minimum_version_id;
     MigrationPriority priority;
     int (*pre_load)(void *opaque);
-    int (*pre_load_errp)(void *opaque, Error **errp);
+    bool (*pre_load_errp)(void *opaque, Error **errp);
     int (*post_load)(void *opaque, int version_id);
-    int (*post_load_errp)(void *opaque, int version_id, Error **errp);
+    bool (*post_load_errp)(void *opaque, int version_id, Error **errp);
     int (*pre_save)(void *opaque);
-    int (*pre_save_errp)(void *opaque, Error **errp);
+    bool (*pre_save_errp)(void *opaque, Error **errp);
     int (*post_save)(void *opaque);
     bool (*needed)(void *opaque);
     bool (*dev_unplug_pending)(void *opaque);

migration/vmstate.c

@@ -154,13 +154,12 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
         return -EINVAL;
     }
     if (vmsd->pre_load_errp) {
-        ret = vmsd->pre_load_errp(opaque, errp);
+        if (!vmsd->pre_load_errp(opaque, errp)) {
-        if (ret < 0) {
             error_prepend(errp, "pre load hook failed for: '%s', "
                           "version_id: %d, minimum version_id: %d: ",
                           vmsd->name, vmsd->version_id,
                           vmsd->minimum_version_id);
-            return ret;
+            return -EINVAL;
         }
     } else if (vmsd->pre_load) {
         ret = vmsd->pre_load(opaque);
@@ -256,11 +255,11 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
         return ret;
     }
     if (vmsd->post_load_errp) {
-        ret = vmsd->post_load_errp(opaque, version_id, errp);
+        if (!vmsd->post_load_errp(opaque, version_id, errp)) {
-        if (ret < 0) {
             error_prepend(errp, "post load hook failed for: %s, version_id: "
                           "%d, minimum_version: %d: ", vmsd->name,
                           vmsd->version_id, vmsd->minimum_version_id);
+            ret = -EINVAL;
         }
     } else if (vmsd->post_load) {
         ret = vmsd->post_load(opaque, version_id);
@@ -438,7 +437,7 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
     trace_vmstate_save_state_top(vmsd->name);
 
     if (vmsd->pre_save_errp) {
-        ret = vmsd->pre_save_errp(opaque, errp);
+        ret = vmsd->pre_save_errp(opaque, errp) ? 0 : -EINVAL;
         trace_vmstate_save_state_pre_save_res(vmsd->name, ret);
         if (ret < 0) {
             error_prepend(errp, "pre-save for %s failed: ", vmsd->name);