migration: Make qemu_savevm_state_non_iterable() take errp

Let the function report errors to upper layers.  Out of three current
users, two of them already process the errors, except one outlier,
qemu_savevm_state_complete_precopy(), where we do it manually for now with
a comment for TODO.

Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Lukas Straub <lukasstraub2@web.de>
Link: https://lore.kernel.org/qemu-devel/20260127185254.3954634-23-peterx@redhat.com
[add space in error_prepend string]
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/migration.c

@@ -2552,9 +2552,9 @@ static int postcopy_start(MigrationState *ms, Error **errp)
      */
     qemu_savevm_send_postcopy_listen(fb);
 
-    ret = qemu_savevm_state_non_iterable(fb);
+    ret = qemu_savevm_state_non_iterable(fb, errp);
     if (ret) {
-        error_setg(errp, "Postcopy save non-iterable device states failed");
+        error_prepend(errp, "Postcopy save non-iterable states failed: ");
         goto fail_closefb;
     }
 
@@ -3687,8 +3687,8 @@ static void *bg_migration_thread(void *opaque)
         goto fail_with_bql;
     }
 
-    if (qemu_savevm_state_non_iterable(fb)) {
-        error_setg(&local_err, "Failed to save non-iterable devices");
+    if (qemu_savevm_state_non_iterable(fb, &local_err)) {
+        error_prepend(&local_err, "Failed to save non-iterable devices ");
         goto fail_with_bql;
     }
 

migration/savevm.c

@@ -1710,13 +1710,12 @@ void qemu_savevm_state_end_precopy(MigrationState *s, QEMUFile *f)
     qemu_savevm_state_vm_desc(s, f);
 }
 
-int qemu_savevm_state_non_iterable(QEMUFile *f)
+int qemu_savevm_state_non_iterable(QEMUFile *f, Error **errp)
 {
     MigrationState *ms = migrate_get_current();
     int64_t start_ts_each, end_ts_each;
     JSONWriter *vmdesc = ms->vmdesc;
     SaveStateEntry *se;
-    Error *local_err = NULL;
     int ret;
 
     /* Making sure cpu states are synchronized before saving non-iterable */
@@ -1730,10 +1729,8 @@ int qemu_savevm_state_non_iterable(QEMUFile *f)
 
         start_ts_each = qemu_clock_get_us(QEMU_CLOCK_REALTIME);
 
-        ret = vmstate_save(f, se, vmdesc, &local_err);
+        ret = vmstate_save(f, se, vmdesc, errp);
         if (ret) {
-            migrate_error_propagate(ms, error_copy(local_err));
-            error_report_err(local_err);
             return ret;
         }
 
@@ -1750,6 +1747,7 @@ int qemu_savevm_state_non_iterable(QEMUFile *f)
 int qemu_savevm_state_complete_precopy(MigrationState *s)
 {
     QEMUFile *f = s->to_dst_file;
+    Error *local_err = NULL;
     int ret;
 
     ret = qemu_savevm_state_complete_precopy_iterable(f, false);
@@ -1757,8 +1755,11 @@ int qemu_savevm_state_complete_precopy(MigrationState *s)
         return ret;
     }
 
-    ret = qemu_savevm_state_non_iterable(f);
+    /* TODO: pass error upper */
+    ret = qemu_savevm_state_non_iterable(f, &local_err);
     if (ret) {
+        migrate_error_propagate(s, error_copy(local_err));
+        error_report_err(local_err);
         return ret;
     }
 

migration/savevm.h

@@ -74,7 +74,7 @@ int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis,
                            Error **errp);
 int qemu_load_device_state(QEMUFile *f, Error **errp);
 int qemu_loadvm_approve_switchover(void);
-int qemu_savevm_state_non_iterable(QEMUFile *f);
+int qemu_savevm_state_non_iterable(QEMUFile *f, Error **errp);
 int qemu_savevm_state_non_iterable_early(QEMUFile *f,
                                          JSONWriter *vmdesc,
                                          Error **errp);