io: add ability to associate an error with a task

Currently when a task fails, the error is never explicitly
associated with the task object, it is just passed along
through the completion callback. This adds the ability to
explicitly associate an error with the task.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

include/io/task.h

@@ -239,6 +239,38 @@ void qio_task_abort(QIOTask *task,
                     Error *err);
 
 
+/**
+ * qio_task_set_error:
+ * @task: the task struct
+ * @err: pointer to the error, or NULL
+ *
+ * Associate an error with the task, which can later
+ * be retrieved with the qio_task_propagate_error()
+ * method. This method takes ownership of @err, so
+ * it is not valid to access it after this call
+ * completes. If @err is NULL this is a no-op. If
+ * this is call multiple times, only the first
+ * provided @err will be recorded, later ones will
+ * be discarded and freed.
+ */
+void qio_task_set_error(QIOTask *task,
+                        Error *err);
+
+
+/**
+ * qio_task_propagate_error:
+ * @task: the task struct
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Propagate the error associated with @task
+ * into @errp.
+ *
+ * Returns: true if an error was propagated, false otherwise
+ */
+bool qio_task_propagate_error(QIOTask *task,
+                              Error **errp);
+
+
 /**
  * qio_task_set_result_pointer:
  * @task: the task struct

io/task.c

@@ -29,6 +29,7 @@ struct QIOTask {
     QIOTaskFunc func;
     gpointer opaque;
     GDestroyNotify destroy;
+    Error *err;
     gpointer result;
     GDestroyNotify destroyResult;
 };
@@ -62,6 +63,9 @@ static void qio_task_free(QIOTask *task)
     if (task->destroyResult) {
         task->destroyResult(task->result);
     }
+    if (task->err) {
+        error_free(task->err);
+    }
     object_unref(task->source);
 
     g_free(task);
@@ -159,6 +163,25 @@ void qio_task_abort(QIOTask *task,
 }
 
 
+void qio_task_set_error(QIOTask *task,
+                        Error *err)
+{
+    error_propagate(&task->err, err);
+}
+
+
+bool qio_task_propagate_error(QIOTask *task,
+                              Error **errp)
+{
+    if (task->err) {
+        error_propagate(errp, task->err);
+        return true;
+    }
+
+    return false;
+}
+
+
 void qio_task_set_result_pointer(QIOTask *task,
                                  gpointer result,
                                  GDestroyNotify destroy)