[PATCH v7 22/24] migration: Capture error in postcopy_ram_listen_thread()

[Arun Menon <armenon@redhat.com>]

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 0a5a8d5948b2b0a3f85163795e84f71903870d25..4a76d7ed730589bae87115368b0bf4819f8b161e 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 810bba9799246c8d57514be0927bb474edee8e9b..202bb9f494c9185434a50967c439ce84e0b3acee 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2095,6 +2095,7 @@ 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));
 
@@ -2111,7 +2112,7 @@ 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
@@ -2137,7 +2138,12 @@ 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,
+                              "loadvm failed during postcopy: %d: ", 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