migration: simplify blockers

Modify migrate_add_blocker and migrate_del_blocker to take an Error **
reason.  This allows migration to own the Error object, so that if
an error occurs in migrate_add_blocker, migration code can free the Error
and clear the client handle, simplifying client code.  It also simplifies
the migrate_del_blocker call site.

In addition, this is a pre-requisite for a proposed future patch that would
add a mode argument to migration requests to support live update, and
maintain a list of blockers for each mode.  A blocker may apply to a single
mode or to multiple modes, and passing Error** will allow one Error object
to be registered for multiple modes.

No functional change.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Tested-by: Michael Galaxy <mgalaxy@akamai.com>
Reviewed-by: Michael Galaxy <mgalaxy@akamai.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <1697634216-84215-1-git-send-email-steven.sistare@oracle.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/migration/migration.c b/migration/migration.c
index 05c0b80..818b02b 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1465,35 +1465,41 @@ int migrate_init(MigrationState *s, Error **errp)
     return 0;
 }
 
-int migrate_add_blocker_internal(Error *reason, Error **errp)
+int migrate_add_blocker_internal(Error **reasonp, Error **errp)
 {
     /* Snapshots are similar to migrations, so check RUN_STATE_SAVE_VM too. */
     if (runstate_check(RUN_STATE_SAVE_VM) || !migration_is_idle()) {
-        error_propagate_prepend(errp, error_copy(reason),
+        error_propagate_prepend(errp, *reasonp,
                                 "disallowing migration blocker "
                                 "(migration/snapshot in progress) for: ");
+        *reasonp = NULL;
         return -EBUSY;
     }
 
-    migration_blockers = g_slist_prepend(migration_blockers, reason);
+    migration_blockers = g_slist_prepend(migration_blockers, *reasonp);
     return 0;
 }
 
-int migrate_add_blocker(Error *reason, Error **errp)
+int migrate_add_blocker(Error **reasonp, Error **errp)
 {
     if (only_migratable) {
-        error_propagate_prepend(errp, error_copy(reason),
+        error_propagate_prepend(errp, *reasonp,
                                 "disallowing migration blocker "
                                 "(--only-migratable) for: ");
+        *reasonp = NULL;
         return -EACCES;
     }
 
-    return migrate_add_blocker_internal(reason, errp);
+    return migrate_add_blocker_internal(reasonp, errp);
 }
 
-void migrate_del_blocker(Error *reason)
+void migrate_del_blocker(Error **reasonp)
 {
-    migration_blockers = g_slist_remove(migration_blockers, reason);
+    if (*reasonp) {
+        migration_blockers = g_slist_remove(migration_blockers, *reasonp);
+        error_free(*reasonp);
+        *reasonp = NULL;
+    }
 }
 
 void qmp_migrate_incoming(const char *uri, Error **errp)