migration: Add error-parameterized function variants in VMSD struct

- We need to have good error reporting in the callbacks in
  VMStateDescription struct. Specifically pre_save, pre_load
  and post_load callbacks.
- It is not possible to change these functions everywhere in one
  patch, therefore, we introduce a duplicate set of callbacks
  with Error object passed to them.
- So, in this commit, we implement 'errp' variants of these callbacks,
  introducing an explicit Error object parameter.
- This is a functional step towards transitioning the entire codebase
  to the new error-parameterized functions.
- Deliberately called in mutual exclusion from their counterparts,
  to prevent conflicts during the transition.
- New impls should preferentally use 'errp' variants of
  these methods, and existing impls incrementally converted.
  The variants without 'errp' are intended to be removed
  once all usage is converted.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Arun Menon <armenon@redhat.com>
Tested-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Link: https://lore.kernel.org/r/20250918-propagate_tpm_error-v14-26-36f11a6fb9d3@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 5fe9bbf390..5567fd78d0 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -200,14 +200,28 @@ struct VMStateDescription {
      * exclusive. For this reason, also early_setup VMSDs are migrated in a
      * QEMU_VM_SECTION_FULL section, while save_setup() data is migrated in
      * a QEMU_VM_SECTION_START section.
+     *
+     * There are duplicate impls of the post/pre save/load hooks.
+     * New impls should preferentally use 'errp' variants of these
+     * methods and existing impls incrementally converted.
+     * The variants without 'errp' are intended to be removed
+     * once all usage is converted.
+     *
+     * For the errp variants,
+     * Returns: 0 on success,
+     *          <0 on error where -value is an error number from errno.h
      */
+
     bool early_setup;
     int version_id;
     int minimum_version_id;
     MigrationPriority priority;
     int (*pre_load)(void *opaque);
+    int (*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);
     int (*pre_save)(void *opaque);
+    int (*pre_save_errp)(void *opaque, Error **errp);
     int (*post_save)(void *opaque);
     bool (*needed)(void *opaque);
     bool (*dev_unplug_pending)(void *opaque);