migration: Add Error** argument to qemu_savevm_state_setup()

This prepares ground for the changes coming next which add an Error**
argument to the .save_setup() handler. Callers of qemu_savevm_state_setup()
now handle the error and fail earlier setting the migration state from
MIGRATION_STATUS_SETUP to MIGRATION_STATUS_FAILED.

In qemu_savevm_state(), move the cleanup to preserve the error
reported by .save_setup() handlers.

Since the previous behavior was to ignore errors at this step of
migration, this change should be examined closely to check that
cleanups are still correctly done.

Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240320064911.545001-7-clg@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 15 insertions, 11 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 6252fc37b7..327e9b346e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1310,11 +1310,11 @@ int qemu_savevm_state_prepare(Error **errp)
     return 0;
 }
 
-void qemu_savevm_state_setup(QEMUFile *f)
+int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
 {
+    ERRP_GUARD();
     MigrationState *ms = migrate_get_current();
     SaveStateEntry *se;
-    Error *local_err = NULL;
     int ret = 0;
 
     json_writer_int64(ms->vmdesc, "page_size", qemu_target_page_size());
@@ -1323,10 +1323,9 @@ void qemu_savevm_state_setup(QEMUFile *f)
     trace_savevm_state_setup();
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
         if (se->vmsd && se->vmsd->early_setup) {
-            ret = vmstate_save(f, se, ms->vmdesc, &local_err);
+            ret = vmstate_save(f, se, ms->vmdesc, errp);
             if (ret) {
-                migrate_set_error(ms, local_err);
-                error_report_err(local_err);
+                migrate_set_error(ms, *errp);
                 qemu_file_set_error(f, ret);
                 break;
             }
@@ -1346,18 +1345,19 @@ void qemu_savevm_state_setup(QEMUFile *f)
         ret = se->ops->save_setup(f, se->opaque);
         save_section_footer(f, se);
         if (ret < 0) {
+            error_setg(errp, "failed to setup SaveStateEntry with id(name): "
+                       "%d(%s): %d", se->section_id, se->idstr, ret);
             qemu_file_set_error(f, ret);
             break;
         }
     }
 
     if (ret) {
-        return;
+        return ret;
     }
 
-    if (precopy_notify(PRECOPY_NOTIFY_SETUP, &local_err)) {
-        error_report_err(local_err);
-    }
+    /* TODO: Should we check that errp is set in case of failure ? */
+    return precopy_notify(PRECOPY_NOTIFY_SETUP, errp);
 }
 
 int qemu_savevm_state_resume_prepare(MigrationState *s)
@@ -1725,7 +1725,10 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
     ms->to_dst_file = f;
 
     qemu_savevm_state_header(f);
-    qemu_savevm_state_setup(f);
+    ret = qemu_savevm_state_setup(f, errp);
+    if (ret) {
+        goto cleanup;
+    }
 
     while (qemu_file_get_error(f) == 0) {
         if (qemu_savevm_state_iterate(f, false) > 0) {
@@ -1738,10 +1741,11 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
         qemu_savevm_state_complete_precopy(f, false, false);
         ret = qemu_file_get_error(f);
     }
-    qemu_savevm_state_cleanup();
     if (ret != 0) {
         error_setg_errno(errp, -ret, "Error while writing VM state");
     }
+cleanup:
+    qemu_savevm_state_cleanup();
 
     if (ret != 0) {
         status = MIGRATION_STATUS_FAILED;