[PULL 06/27] migration: Propagate errors in migration_completion_precopy()

["Cédric Le Goater" <clg@redhat.com>]

From: Avihai Horon <avihaih@nvidia.com>

migration_completion_precopy() doesn't propagate errors to migration
core which leads to error information loss. Fix that.

This prepares for a follow-up where migration_switchover_start() can
fail on switchover-ack and still report a useful error.

Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Link: https://lore.kernel.org/qemu-devel/20260706085211.13905-2-avihaih@nvidia.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
 migration/savevm.h    |  2 +-
 migration/migration.c | 13 ++++++++-----
 migration/savevm.c    | 29 +++++++++++++++++------------
 3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/migration/savevm.h b/migration/savevm.h
index 96fdf96d4ef6f7fd174f50e8c1402f0b6d6b9e1f..b6bb4fa977fae84ed121b0668cdefdf49e3d9c67 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -44,7 +44,7 @@ void qemu_savevm_state_header(QEMUFile *f);
 int qemu_savevm_state_iterate(QEMUFile *f, bool postcopy);
 void qemu_savevm_state_cleanup(void);
 void qemu_savevm_state_complete_postcopy(QEMUFile *f);
-int qemu_savevm_state_complete_precopy(MigrationState *s);
+int qemu_savevm_state_complete_precopy(MigrationState *s, Error **errp);
 void qemu_savevm_query_pending(MigPendingData *pending, bool exact);
 int qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy);
 bool qemu_savevm_state_postcopy_prepare(QEMUFile *f, Error **errp);
diff --git a/migration/migration.c b/migration/migration.c
index 0f56432d903054883679a66ac5bd853577b5df66..7e0a0bea7ae823ee5ef6e7ba8876c9222f9ac834 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2820,7 +2820,7 @@ static bool migration_switchover_start(MigrationState *s, Error **errp)
     return true;
 }
 
-static int migration_completion_precopy(MigrationState *s)
+static int migration_completion_precopy(MigrationState *s, Error **errp)
 {
     int ret;
 
@@ -2829,16 +2829,17 @@ static int migration_completion_precopy(MigrationState *s)
     if (!migrate_mode_is_cpr()) {
         ret = migration_stop_vm(s, RUN_STATE_FINISH_MIGRATE);
         if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to stop the VM");
             goto out_unlock;
         }
     }
 
-    if (!migration_switchover_start(s, NULL)) {
+    if (!migration_switchover_start(s, errp)) {
         ret = -EFAULT;
         goto out_unlock;
     }
 
-    ret = qemu_savevm_state_complete_precopy(s);
+    ret = qemu_savevm_state_complete_precopy(s, errp);
 out_unlock:
     bql_unlock();
     return ret;
@@ -2875,7 +2876,7 @@ static void migration_completion(MigrationState *s)
     Error *local_err = NULL;
 
     if (s->state == MIGRATION_STATUS_ACTIVE) {
-        ret = migration_completion_precopy(s);
+        ret = migration_completion_precopy(s, &local_err);
     } else if (s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE) {
         migration_completion_postcopy(s);
     } else {
@@ -2906,7 +2907,9 @@ static void migration_completion(MigrationState *s)
     return;
 
 fail:
-    if (qemu_file_get_error_obj(s->to_dst_file, &local_err)) {
+    if (local_err) {
+        migrate_error_propagate(s, local_err);
+    } else if (qemu_file_get_error_obj(s->to_dst_file, &local_err)) {
         migrate_error_propagate(s, local_err);
     } else if (ret) {
         error_setg_errno(&local_err, -ret, "Error in migration completion");
diff --git a/migration/savevm.c b/migration/savevm.c
index 23adaf9dd9263b8dafe808f0637724fe4a5482b2..7e2a0c2b4a7470d9c2159eac1d18ae891740fe3e 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1771,28 +1771,34 @@ int qemu_savevm_state_non_iterable(QEMUFile *f, Error **errp)
     return 0;
 }
 
-int qemu_savevm_state_complete_precopy(MigrationState *s)
+int qemu_savevm_state_complete_precopy(MigrationState *s, Error **errp)
 {
+    ERRP_GUARD();
     QEMUFile *f = s->to_dst_file;
-    Error *local_err = NULL;
     int ret;
 
     ret = qemu_savevm_state_complete_precopy_iterable(f, false);
     if (ret) {
+        qemu_file_get_error_obj(f, errp);
+        error_prepend(errp, "Failed to save iterable device state: ");
         return ret;
     }
 
-    /* TODO: pass error upper */
-    ret = qemu_savevm_state_non_iterable(f, &local_err);
+    ret = qemu_savevm_state_non_iterable(f, errp);
     if (ret) {
-        migrate_error_propagate(s, error_copy(local_err));
-        error_report_err(local_err);
         return ret;
     }
 
     qemu_savevm_state_end_precopy(s, f);
 
-    return qemu_fflush(f);
+    ret = qemu_fflush(f);
+    if (ret) {
+        qemu_file_get_error_obj(f, errp);
+        error_prepend(errp, "Failed to flush QEMUFile: ");
+        return ret;
+    }
+
+    return 0;
 }
 
 void qemu_savevm_query_pending(MigPendingData *pending, bool exact)
@@ -1874,13 +1880,12 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
     }
 
     ret = qemu_file_get_error(f);
-    if (ret == 0) {
-        qemu_savevm_state_complete_precopy(ms);
-        ret = qemu_file_get_error(f);
-    }
-    if (ret != 0) {
+    if (ret) {
         error_setg_errno(errp, -ret, "Error while writing VM state");
+        goto cleanup;
     }
+
+    ret = qemu_savevm_state_complete_precopy(ms, errp);
 cleanup:
     qemu_savevm_state_cleanup();
 
-- 
2.54.0