[PATCH for-11.0 v2 7/7] migration: Replace migrate_set_error() with migrate_error_propagate()

[Peter Xu <peterx@redhat.com>]

migrate_set_error() currently doesn't take ownership of the error being
passed in.  It's not aligned with the error API and meanwhile it also
makes most of the caller free the error explicitly.

Change the API to take the ownership of the Error object instead.  This
should save a lot of error_copy() invocations.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.h            |  2 +-
 migration/cpr-exec.c             |  5 ++--
 migration/migration.c            | 44 +++++++++++++++-----------------
 migration/multifd-device-state.c |  5 +---
 migration/multifd.c              | 19 +++++++-------
 migration/postcopy-ram.c         |  5 ++--
 migration/ram.c                  |  4 +--
 migration/savevm.c               | 16 +++++-------
 8 files changed, 43 insertions(+), 57 deletions(-)

diff --git a/migration/migration.h b/migration/migration.h
index 213b33fe6e..e4b4f25deb 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -525,7 +525,7 @@ void migration_incoming_process(void);
 
 bool  migration_has_all_channels(void);
 
-void migrate_set_error(MigrationState *s, const Error *error);
+void migrate_error_propagate(MigrationState *s, Error *error);
 bool migrate_has_error(MigrationState *s);
 
 void migration_connect(MigrationState *s, Error *error_in);
diff --git a/migration/cpr-exec.c b/migration/cpr-exec.c
index 0b8344a86f..da287d8031 100644
--- a/migration/cpr-exec.c
+++ b/migration/cpr-exec.c
@@ -158,8 +158,9 @@ static void cpr_exec_cb(void *opaque)
 
     error_report_err(error_copy(err));
     migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
-    migrate_set_error(s, err);
-    error_free(err);
+
+    migrate_error_propagate(s, err);
+    /* We must reset the error because it'll be reused later */
     err = NULL;
 
     /* Note, we can go from state COMPLETED to FAILED */
diff --git a/migration/migration.c b/migration/migration.c
index 0ff8b31a88..70813e5006 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -914,9 +914,7 @@ process_incoming_migration_co(void *opaque)
 fail:
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_FAILED);
-    migrate_set_error(s, local_err);
-    error_free(local_err);
-
+    migrate_error_propagate(s, local_err);
     migration_incoming_state_destroy();
 
     if (mis->exit_on_error) {
@@ -1548,14 +1546,20 @@ static void migration_cleanup_bh(void *opaque)
     migration_cleanup(opaque);
 }
 
-void migrate_set_error(MigrationState *s, const Error *error)
+/*
+ * Propagate the Error* object to migration core.  The caller mustn't
+ * reference the error pointer after the function returned, because the
+ * Error* object might be freed.
+ */
+void migrate_error_propagate(MigrationState *s, Error *error)
 {
     QEMU_LOCK_GUARD(&s->error_mutex);
-
     trace_migrate_error(error_get_pretty(error));
 
     if (!s->error) {
-        s->error = error_copy(error);
+        s->error = error;
+    } else {
+        error_free(error);
     }
 }
 
@@ -1601,8 +1605,7 @@ static void migration_connect_error_propagate(MigrationState *s, Error *error)
     }
 
     migrate_set_state(&s->state, current, next);
-    migrate_set_error(s, error);
-    error_free(error);
+    migrate_error_propagate(s, error);
 }
 
 void migration_cancel(void)
@@ -2014,8 +2017,7 @@ void qmp_migrate_pause(Error **errp)
 
         /* Tell the core migration that we're pausing */
         error_setg(&error, "Postcopy migration is paused by the user");
-        migrate_set_error(ms, error);
-        error_free(error);
+        migrate_error_propagate(ms, error);
 
         qemu_mutex_lock(&ms->qemu_file_lock);
         if (ms->to_dst_file) {
@@ -2647,8 +2649,7 @@ static void *source_return_path_thread(void *opaque)
 
 out:
     if (err) {
-        migrate_set_error(ms, err);
-        error_free(err);
+        migrate_error_propagate(ms, err);
         trace_source_return_path_thread_bad_end();
     }
 
@@ -3094,12 +3095,10 @@ static void migration_completion(MigrationState *s)
 
 fail:
     if (qemu_file_get_error_obj(s->to_dst_file, &local_err)) {
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(s, local_err);
     } else if (ret) {
         error_setg_errno(&local_err, -ret, "Error in migration completion");
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(s, local_err);
     }
 
     if (s->state != MIGRATION_STATUS_CANCELLING) {
@@ -3326,8 +3325,7 @@ static MigThrError migration_detect_error(MigrationState *s)
     }
 
     if (local_error) {
-        migrate_set_error(s, local_error);
-        error_free(local_error);
+        migrate_error_propagate(s, local_error);
     }
 
     if (state == MIGRATION_STATUS_POSTCOPY_ACTIVE && ret) {
@@ -3522,7 +3520,7 @@ static MigIterateState migration_iteration_run(MigrationState *s)
         if (must_precopy <= s->threshold_size &&
             can_switchover && qatomic_read(&s->start_postcopy)) {
             if (postcopy_start(s, &local_err)) {
-                migrate_set_error(s, local_err);
+                migrate_error_propagate(s, error_copy(local_err));
                 error_report_err(local_err);
             }
             return MIG_ITERATE_SKIP;
@@ -3819,8 +3817,7 @@ static void *migration_thread(void *opaque)
      * devices to unplug. This to preserve migration state transitions.
      */
     if (ret) {
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(s, local_err);
         migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                           MIGRATION_STATUS_FAILED);
         goto out;
@@ -3944,8 +3941,7 @@ static void *bg_migration_thread(void *opaque)
      * devices to unplug. This to preserve migration state transitions.
      */
     if (ret) {
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(s, local_err);
         migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
                           MIGRATION_STATUS_FAILED);
         goto fail_setup;
@@ -4127,7 +4123,7 @@ void migration_connect(MigrationState *s, Error *error_in)
     return;
 
 fail:
-    migrate_set_error(s, local_err);
+    migrate_error_propagate(s, error_copy(local_err));
     if (s->state != MIGRATION_STATUS_CANCELLING) {
         migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
     }
diff --git a/migration/multifd-device-state.c b/migration/multifd-device-state.c
index db3239fef5..91d5d81556 100644
--- a/migration/multifd-device-state.c
+++ b/migration/multifd-device-state.c
@@ -143,8 +143,6 @@ static int multifd_device_state_save_thread(void *opaque)
     Error *local_err = NULL;
 
     if (!data->hdlr(data, &local_err)) {
-        MigrationState *s = migrate_get_current();
-
         /*
          * Can't call abort_device_state_save_threads() here since new
          * save threads could still be in process of being launched
@@ -158,8 +156,7 @@ static int multifd_device_state_save_thread(void *opaque)
          * In case of multiple save threads failing which thread error
          * return we end setting is purely arbitrary.
          */
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(migrate_get_current(), local_err);
     }
 
     return 0;
diff --git a/migration/multifd.c b/migration/multifd.c
index 52e4d25857..bf6da85af8 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -428,8 +428,9 @@ static void multifd_send_error_propagate(Error *err)
 
     if (err) {
         MigrationState *s = migrate_get_current();
-        migrate_set_error(s, err);
-        error_free(err);
+
+        migrate_error_propagate(s, err);
+
         if (s->state == MIGRATION_STATUS_SETUP ||
             s->state == MIGRATION_STATUS_PRE_SWITCHOVER ||
             s->state == MIGRATION_STATUS_DEVICE ||
@@ -588,8 +589,7 @@ void multifd_send_shutdown(void)
         Error *local_err = NULL;
 
         if (!multifd_send_cleanup_channel(p, &local_err)) {
-            migrate_set_error(migrate_get_current(), local_err);
-            error_free(local_err);
+            migrate_error_propagate(migrate_get_current(), local_err);
         }
     }
 
@@ -962,8 +962,7 @@ bool multifd_send_setup(void)
         p->write_flags = 0;
 
         if (!multifd_new_send_channel_create(p, &local_err)) {
-            migrate_set_error(s, local_err);
-            error_free(local_err);
+            migrate_error_propagate(s, local_err);
             ret = -1;
         }
     }
@@ -987,8 +986,7 @@ bool multifd_send_setup(void)
 
         ret = multifd_send_state->ops->send_setup(p, &local_err);
         if (ret) {
-            migrate_set_error(s, local_err);
-            error_free(local_err);
+            migrate_error_propagate(s, local_err);
             goto err;
         }
         assert(p->iov);
@@ -1067,8 +1065,9 @@ static void multifd_recv_terminate_threads(Error *err)
 
     if (err) {
         MigrationState *s = migrate_get_current();
-        migrate_set_error(s, err);
-        error_free(err);
+
+        migrate_error_propagate(s, err);
+
         if (s->state == MIGRATION_STATUS_SETUP ||
             s->state == MIGRATION_STATUS_ACTIVE) {
             migrate_set_state(&s->state, s->state,
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 7c9fe61041..dd8e31f5ae 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -1927,8 +1927,7 @@ postcopy_preempt_send_channel_done(MigrationState *s,
                                    QIOChannel *ioc, Error *local_err)
 {
     if (local_err) {
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(s, local_err);
     } else {
         migration_ioc_register_yank(ioc);
         s->postcopy_qemufile_src = qemu_file_new_output(ioc);
@@ -2162,7 +2161,7 @@ static void *postcopy_listen_thread(void *opaque)
              * exit depending on if postcopy-exit-on-error is true, but the
              * migration cannot be recovered.
              */
-            migrate_set_error(migr, local_err);
+            migrate_error_propagate(migr, error_copy(local_err));
             error_report_err(local_err);
             migrate_set_state(&mis->state, mis->state, MIGRATION_STATUS_FAILED);
             goto out;
diff --git a/migration/ram.c b/migration/ram.c
index 29f016cb25..a2f456d858 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -4730,9 +4730,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
          * Abort and indicate a proper reason.
          */
         error_setg(&err, "RAM block '%s' resized during precopy.", rb->idstr);
-        migrate_set_error(migrate_get_current(), err);
-        error_free(err);
-
+        migrate_error_propagate(migrate_get_current(), err);
         migration_cancel();
     }
 
diff --git a/migration/savevm.c b/migration/savevm.c
index 638e9b364f..67f10a5dbe 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1125,13 +1125,12 @@ void qemu_savevm_send_open_return_path(QEMUFile *f)
 int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len)
 {
     uint32_t tmp;
-    MigrationState *ms = migrate_get_current();
     Error *local_err = NULL;
 
     if (len > MAX_VM_CMD_PACKAGED_SIZE) {
         error_setg(&local_err, "%s: Unreasonably large packaged state: %zu",
                      __func__, len);
-        migrate_set_error(ms, local_err);
+        migrate_error_propagate(migrate_get_current(), error_copy(local_err));
         error_report_err(local_err);
         return -1;
     }
@@ -1373,7 +1372,7 @@ int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
         if (se->vmsd && se->vmsd->early_setup) {
             ret = vmstate_save(f, se, vmdesc, errp);
             if (ret) {
-                migrate_set_error(ms, *errp);
+                migrate_error_propagate(ms, error_copy(*errp));
                 qemu_file_set_error(f, ret);
                 break;
             }
@@ -1681,7 +1680,7 @@ int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
 
         ret = vmstate_save(f, se, vmdesc, &local_err);
         if (ret) {
-            migrate_set_error(ms, local_err);
+            migrate_error_propagate(ms, error_copy(local_err));
             error_report_err(local_err);
             qemu_file_set_error(f, ret);
             return ret;
@@ -1858,7 +1857,6 @@ void qemu_savevm_live_state(QEMUFile *f)
 
 int qemu_save_device_state(QEMUFile *f)
 {
-    MigrationState *ms = migrate_get_current();
     Error *local_err = NULL;
     SaveStateEntry *se;
 
@@ -1876,7 +1874,8 @@ int qemu_save_device_state(QEMUFile *f)
         }
         ret = vmstate_save(f, se, NULL, &local_err);
         if (ret) {
-            migrate_set_error(ms, local_err);
+            migrate_error_propagate(migrate_get_current(),
+                                    error_copy(local_err));
             error_report_err(local_err);
             return ret;
         }
@@ -2826,8 +2825,6 @@ static int qemu_loadvm_load_thread(void *thread_opaque)
     Error *local_err = NULL;
 
     if (!data->function(data->opaque, &mis->load_threads_abort, &local_err)) {
-        MigrationState *s = migrate_get_current();
-
         /*
          * Can't set load_threads_abort here since processing of main migration
          * channel data could still be happening, resulting in launching of new
@@ -2840,8 +2837,7 @@ static int qemu_loadvm_load_thread(void *thread_opaque)
          * In case of multiple load threads failing which thread error
          * return we end setting is purely arbitrary.
          */
-        migrate_set_error(s, local_err);
-        error_free(local_err);
+        migrate_error_propagate(migrate_get_current(), local_err);
     }
 
     return 0;
-- 
2.50.1