migration: push Error **errp into qemu_loadvm_state_main()

This is an incremental step in converting vmstate loading
code to report error via Error objects instead of directly
printing it to console/monitor.
It is ensured that qemu_loadvm_state_main() must report an error
in errp, in case of failure.

Set errp explicitly if it is NULL in case of failure in the out
section. This will be removed in the subsequent patch when all of
the calls are converted to passing errp.

The error message in the default case of qemu_loadvm_state_main()
has the word "savevm". This is removed because it can confuse the
user while reading destination side error logs.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
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-v14-9-36f11a6fb9d3@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

3 files changed, 20 insertions, 22 deletions

diff --git a/migration/colo.c b/migration/colo.c
index a426ec5b60..ad50a3abc9 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -686,11 +686,10 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
 
     bql_lock();
     cpu_synchronize_all_states();
-    ret = qemu_loadvm_state_main(mis->from_src_file, mis);
+    ret = qemu_loadvm_state_main(mis->from_src_file, mis, errp);
     bql_unlock();
 
     if (ret < 0) {
-        error_setg(errp, "Load VM's live state (ram) error");
         return;
     }
 
diff --git a/migration/savevm.c b/migration/savevm.c
index 9e30718995..f1338f5cf6 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2105,7 +2105,7 @@ static void *postcopy_ram_listen_thread(void *opaque)
     qemu_file_set_blocking(f, true, &error_fatal);
 
     /* TODO: sanity check that only postcopiable data will be loaded here */
-    load_res = qemu_loadvm_state_main(f, mis);
+    load_res = qemu_loadvm_state_main(f, mis, &error_fatal);
 
     /*
      * This is tricky, but, mis->from_src_file can change after it
@@ -2456,10 +2456,7 @@ static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis, Error **errp)
         qemu_coroutine_yield();
     } while (1);
 
-    ret = qemu_loadvm_state_main(packf, mis);
-    if (ret < 0) {
-        error_setg(errp, "VM state load failed: %d", ret);
-    }
+    ret = qemu_loadvm_state_main(packf, mis, errp);
     trace_loadvm_handle_cmd_packaged_main(ret);
     qemu_fclose(packf);
     object_unref(OBJECT(bioc));
@@ -3080,18 +3077,22 @@ static bool postcopy_pause_incoming(MigrationIncomingState *mis)
     return true;
 }
 
-int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis)
+int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis,
+                           Error **errp)
 {
+    ERRP_GUARD();
     uint8_t section_type;
     int ret = 0;
-    Error *local_err = NULL;
 
 retry:
     while (true) {
         section_type = qemu_get_byte(f);
 
-        ret = qemu_file_get_error_obj_any(f, mis->postcopy_qemufile_dst, NULL);
+        ret = qemu_file_get_error_obj_any(f, mis->postcopy_qemufile_dst, errp);
         if (ret) {
+            error_prepend(errp,
+                          "Failed to load section ID: stream error: %d: ",
+                          ret);
             break;
         }
 
@@ -3112,10 +3113,7 @@ retry:
             }
             break;
         case QEMU_VM_COMMAND:
-            ret = loadvm_process_command(f, &local_err);
-            if (ret < 0) {
-                error_report_err(local_err);
-            }
+            ret = loadvm_process_command(f, errp);
             trace_qemu_loadvm_state_section_command(ret);
             if ((ret < 0) || (ret == LOADVM_QUIT)) {
                 goto out;
@@ -3125,7 +3123,7 @@ retry:
             /* This is the end of migration */
             goto out;
         default:
-            error_report("Unknown savevm section type %d", section_type);
+            error_setg(errp, "Unknown section type %d", section_type);
             ret = -EINVAL;
             goto out;
         }
@@ -3133,6 +3131,9 @@ retry:
 
 out:
     if (ret < 0) {
+        if (*errp == NULL) {
+            error_setg(errp, "Loading VM state failed: %d", ret);
+        }
         qemu_file_set_error(f, ret);
 
         /* Cancel bitmaps incoming regardless of recovery */
@@ -3153,6 +3154,7 @@ out:
             migrate_postcopy_ram() && postcopy_pause_incoming(mis)) {
             /* Reset f to point to the newly created channel */
             f = mis->from_src_file;
+            error_free_or_abort(errp);
             goto retry;
         }
     }
@@ -3186,10 +3188,7 @@ int qemu_loadvm_state(QEMUFile *f, Error **errp)
 
     cpu_synchronize_all_pre_loadvm();
 
-    ret = qemu_loadvm_state_main(f, mis);
-    if (ret < 0) {
-        error_setg(errp, "Load VM state failed: %d", ret);
-    }
+    ret = qemu_loadvm_state_main(f, mis, errp);
     qemu_event_set(&mis->main_thread_load_event);
 
     trace_qemu_loadvm_state_post_main(ret);
@@ -3270,9 +3269,8 @@ int qemu_load_device_state(QEMUFile *f, Error **errp)
     int ret;
 
     /* Load QEMU_VM_SECTION_FULL section */
-    ret = qemu_loadvm_state_main(f, mis);
+    ret = qemu_loadvm_state_main(f, mis, errp);
     if (ret < 0) {
-        error_setg(errp, "Failed to load device state: %d", ret);
         return ret;
     }
 
diff --git a/migration/savevm.h b/migration/savevm.h
index b12681839f..c337e3e3d1 100644
--- a/migration/savevm.h
+++ b/migration/savevm.h
@@ -66,7 +66,8 @@ int qemu_save_device_state(QEMUFile *f);
 
 int qemu_loadvm_state(QEMUFile *f, Error **errp);
 void qemu_loadvm_state_cleanup(MigrationIncomingState *mis);
-int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis);
+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_complete_precopy_non_iterable(QEMUFile *f,