This is an incremental step in converting vmstate loading
code to report error via Error objects instead of directly
printing it to console/monitor.
postcopy_ram_listen_thread() calls qemu_loadvm_state_main()
to load the vm, and in case of a failure, it should set the error
in the migration object.

When postcopy live migration runs, the device states are loaded by
both the qemu coroutine process_incoming_migration_co() and the
postcopy_ram_listen_thread(). Therefore, it is important that the
coroutine also reports the error in case of failure, with
error_report_err(). Otherwise, the source qemu will not display
any errors before going into the postcopy pause state.

Signed-off-by: Arun Menon <armenon@redhat.com>
---
 migration/migration.c |  2 +-
 migration/savevm.c    | 10 ++++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 1f0a8bd6ab28ff09bb76919564bdbfbde35c5e42..efd02d917cfe4d1221907123eadd98932b02e8bc 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -925,7 +925,7 @@ fail:
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_FAILED);
     migrate_set_error(s, local_err);
-    error_free(local_err);
+    error_report_err(local_err);
 
     migration_incoming_state_destroy();
 
diff --git a/migration/savevm.c b/migration/savevm.c
index 0fff65c96344c65191353311e72730cd6e3bfb23..4f67eebe5321c175d51e8029e36ceb336c98ad1f 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2086,6 +2086,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
     QEMUFile *f = mis->from_src_file;
     int load_res;
     MigrationState *migr = migrate_get_current();
+    Error *local_err = NULL;
 
     object_ref(OBJECT(migr));
 
@@ -2102,7 +2103,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
     qemu_file_set_blocking(f, true);
 
     /* TODO: sanity check that only postcopiable data will be loaded here */
-    load_res = qemu_loadvm_state_main(f, mis, NULL);
+    load_res = qemu_loadvm_state_main(f, mis, &local_err);
 
     /*
      * This is tricky, but, mis->from_src_file can change after it
@@ -2128,7 +2129,12 @@ static void *postcopy_ram_listen_thread(void *opaque)
                          __func__, load_res);
             load_res = 0; /* prevent further exit() */
         } else {
-            error_report("%s: loadvm failed: %d", __func__, load_res);
+            if (local_err != NULL) {
+                error_prepend(&local_err, "%s: loadvm failed: %d", __func__,
+                              load_res);
+                migrate_set_error(migr, local_err);
+                error_report_err(local_err);
+            }
             migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
                                            MIGRATION_STATUS_FAILED);
         }

-- 
2.50.0

On Thu, Jul 17, 2025 at 06:07:44AM +0530, Arun Menon wrote:
> This is an incremental step in converting vmstate loading
> code to report error via Error objects instead of directly
> printing it to console/monitor.
> postcopy_ram_listen_thread() calls qemu_loadvm_state_main()
> to load the vm, and in case of a failure, it should set the error
> in the migration object.
> 
> When postcopy live migration runs, the device states are loaded by
> both the qemu coroutine process_incoming_migration_co() and the
> postcopy_ram_listen_thread(). Therefore, it is important that the
> coroutine also reports the error in case of failure, with
> error_report_err(). Otherwise, the source qemu will not display
> any errors before going into the postcopy pause state.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  migration/migration.c |  2 +-
>  migration/savevm.c    | 10 ++++++++--
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 


> diff --git a/migration/savevm.c b/migration/savevm.c
> index 0fff65c96344c65191353311e72730cd6e3bfb23..4f67eebe5321c175d51e8029e36ceb336c98ad1f 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -2086,6 +2086,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      QEMUFile *f = mis->from_src_file;
>      int load_res;
>      MigrationState *migr = migrate_get_current();
> +    Error *local_err = NULL;
>  
>      object_ref(OBJECT(migr));
>  
> @@ -2102,7 +2103,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      qemu_file_set_blocking(f, true);
>  
>      /* TODO: sanity check that only postcopiable data will be loaded here */
> -    load_res = qemu_loadvm_state_main(f, mis, NULL);
> +    load_res = qemu_loadvm_state_main(f, mis, &local_err);
>  
>      /*
>       * This is tricky, but, mis->from_src_file can change after it
> @@ -2128,7 +2129,12 @@ static void *postcopy_ram_listen_thread(void *opaque)
>                           __func__, load_res);
>              load_res = 0; /* prevent further exit() */
>          } else {
> -            error_report("%s: loadvm failed: %d", __func__, load_res);
> +            if (local_err != NULL) {
> +                error_prepend(&local_err, "%s: loadvm failed: %d", __func__,
> +                              load_res);

IMHO __func__ is redundant if you change the message
to be 'loadvm failed during postcopy' like the earlier part
fo the "if { " does.

> +                migrate_set_error(migr, local_err);
> +                error_report_err(local_err);
> +            }
>              migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
>                                             MIGRATION_STATUS_FAILED);

With regards,
Daniel
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