Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 350 insertions, 0 deletions

diff --git a/include/io/task.h b/include/io/task.h
new file mode 100644
index 000000000..beec4f5cf
--- /dev/null
+++ b/include/io/task.h
@@ -0,0 +1,350 @@
+/*
+ * QEMU I/O task
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QIO_TASK_H
+#define QIO_TASK_H
+
+typedef struct QIOTask QIOTask;
+
+typedef void (*QIOTaskFunc)(QIOTask *task,
+                            gpointer opaque);
+
+typedef void (*QIOTaskWorker)(QIOTask *task,
+                              gpointer opaque);
+
+/**
+ * QIOTask:
+ *
+ * The QIOTask object provides a simple mechanism for reporting
+ * success / failure of long running background operations.
+ *
+ * A object on which the operation is to be performed could have
+ * a public API which accepts a task callback:
+ *
+ * <example>
+ *   <title>Task function signature</title>
+ *   <programlisting>
+ *  void myobject_operation(QMyObject *obj,
+ *                          QIOTaskFunc *func,
+ *                          gpointer opaque,
+ *                          GDestroyNotify notify);
+ *   </programlisting>
+ * </example>
+ *
+ * The 'func' parameter is the callback to be invoked, and 'opaque'
+ * is data to pass to it. The optional 'notify' function is used
+ * to free 'opaque' when no longer needed.
+ *
+ * When the operation completes, the 'func' callback will be
+ * invoked, allowing the calling code to determine the result
+ * of the operation. An example QIOTaskFunc implementation may
+ * look like
+ *
+ * <example>
+ *   <title>Task callback implementation</title>
+ *   <programlisting>
+ *  static void myobject_operation_notify(QIOTask *task,
+ *                                        gpointer opaque)
+ *  {
+ *      Error *err = NULL;
+ *      if (qio_task_propagate_error(task, &err)) {
+ *          ...deal with the failure...
+ *          error_free(err);
+ *      } else {
+ *          QMyObject *src = QMY_OBJECT(qio_task_get_source(task));
+ *          ...deal with the completion...
+ *      }
+ *  }
+ *   </programlisting>
+ * </example>
+ *
+ * Now, lets say the implementation of the method using the
+ * task wants to set a timer to run once a second checking
+ * for completion of some activity. It would do something
+ * like
+ *
+ * <example>
+ *   <title>Task function implementation</title>
+ *   <programlisting>
+ *    void myobject_operation(QMyObject *obj,
+ *                            QIOTaskFunc *func,
+ *                            gpointer opaque,
+ *                            GDestroyNotify notify)
+ *    {
+ *      QIOTask *task;
+ *
+ *      task = qio_task_new(OBJECT(obj), func, opaque, notify);
+ *
+ *      g_timeout_add_full(G_PRIORITY_DEFAULT,
+ *                         1000,
+ *                         myobject_operation_timer,
+ *                         task,
+ *                         NULL);
+ *    }
+ *   </programlisting>
+ * </example>
+ *
+ * It could equally have setup a watch on a file descriptor or
+ * created a background thread, or something else entirely.
+ * Notice that the source object is passed to the task, and
+ * QIOTask will hold a reference on that. This ensure that
+ * the QMyObject instance cannot be garbage collected while
+ * the async task is still in progress.
+ *
+ * In this case, myobject_operation_timer will fire after
+ * 3 secs and do
+ *
+ * <example>
+ *   <title>Task timer function</title>
+ *   <programlisting>
+ *   gboolean myobject_operation_timer(gpointer opaque)
+ *   {
+ *      QIOTask *task = QIO_TASK(opaque);
+ *      Error *err = NULL;
+ *
+ *      ...check something important...
+ *       if (err) {
+ *           qio_task_set_error(task, err);
+ *           qio_task_complete(task);
+ *           return FALSE;
+ *       } else if (...work is completed ...) {
+ *           qio_task_complete(task);
+ *           return FALSE;
+ *       }
+ *       ...carry on polling ...
+ *       return TRUE;
+ *   }
+ *   </programlisting>
+ * </example>
+ *
+ * The 'qio_task_complete' call in this method will trigger
+ * the callback func 'myobject_operation_notify' shown
+ * earlier to deal with the results.
+ *
+ * Once this function returns false, object_unref will be called
+ * automatically on the task causing it to be released and the
+ * ref on QMyObject dropped too.
+ *
+ * The QIOTask module can also be used to perform operations
+ * in a background thread context, while still reporting the
+ * results in the main event thread. This allows code which
+ * cannot easily be rewritten to be asychronous (such as DNS
+ * lookups) to be easily run non-blocking. Reporting the
+ * results in the main thread context means that the caller
+ * typically does not need to be concerned about thread
+ * safety wrt the QEMU global mutex.
+ *
+ * For example, the socket_listen() method will block the caller
+ * while DNS lookups take place if given a name, instead of IP
+ * address. The C library often do not provide a practical async
+ * DNS API, so the to get non-blocking DNS lookups in a portable
+ * manner requires use of a thread. So achieve a non-blocking
+ * socket listen using QIOTask would require:
+ *
+ * <example>
+ *    static void myobject_listen_worker(QIOTask *task,
+ *                                       gpointer opaque)
+ *    {
+ *       QMyObject obj = QMY_OBJECT(qio_task_get_source(task));
+ *       SocketAddress *addr = opaque;
+ *       Error *err = NULL;
+ *
+ *       obj->fd = socket_listen(addr, &err);
+ *
+         qio_task_set_error(task, err);
+ *    }
+ *
+ *    void myobject_listen_async(QMyObject *obj,
+ *                               SocketAddress *addr,
+ *                               QIOTaskFunc *func,
+ *                               gpointer opaque,
+ *                               GDestroyNotify notify)
+ *    {
+ *      QIOTask *task;
+ *      SocketAddress *addrCopy;
+ *
+ *      addrCopy = QAPI_CLONE(SocketAddress, addr);
+ *      task = qio_task_new(OBJECT(obj), func, opaque, notify);
+ *
+ *      qio_task_run_in_thread(task, myobject_listen_worker,
+ *                             addrCopy,
+ *                             qapi_free_SocketAddress);
+ *    }
+ * </example>
+ *
+ * NB, The 'func' callback passed into myobject_listen_async
+ * will be invoked from the main event thread, despite the
+ * actual operation being performed in a different thread.
+ */
+
+/**
+ * qio_task_new:
+ * @source: the object on which the operation is invoked
+ * @func: the callback to invoke when the task completes
+ * @opaque: opaque data to pass to @func when invoked
+ * @destroy: optional callback to free @opaque
+ *
+ * Creates a new task struct to track completion of a
+ * background operation running on the object @source.
+ * When the operation completes or fails, the callback
+ * @func will be invoked. The callback can access the
+ * 'err' attribute in the task object to determine if
+ * the operation was successful or not.
+ *
+ * The returned task will be released when qio_task_complete()
+ * is invoked.
+ *
+ * Returns: the task struct
+ */
+QIOTask *qio_task_new(Object *source,
+                      QIOTaskFunc func,
+                      gpointer opaque,
+                      GDestroyNotify destroy);
+
+/**
+ * qio_task_run_in_thread:
+ * @task: the task struct
+ * @worker: the function to invoke in a thread
+ * @opaque: opaque data to pass to @worker
+ * @destroy: function to free @opaque
+ * @context: the context to run the complete hook. If %NULL, the
+ *           default context will be used.
+ *
+ * Run a task in a background thread. When @worker
+ * returns it will call qio_task_complete() in
+ * the thread that is running the main loop associated
+ * with @context.
+ */
+void qio_task_run_in_thread(QIOTask *task,
+                            QIOTaskWorker worker,
+                            gpointer opaque,
+                            GDestroyNotify destroy,
+                            GMainContext *context);
+
+
+/**
+ * qio_task_wait_thread:
+ * @task: the task struct
+ *
+ * Wait for completion of a task that was previously
+ * invoked using qio_task_run_in_thread. This MUST
+ * ONLY be invoked if the task has not already
+ * completed, since after the completion callback
+ * is invoked, @task will have been freed.
+ *
+ * To avoid racing with execution of the completion
+ * callback provided with qio_task_new, this method
+ * MUST ONLY be invoked from the thread that is
+ * running the main loop associated with @context
+ * parameter to qio_task_run_in_thread.
+ *
+ * When the thread has completed, the completion
+ * callback provided to qio_task_new will be invoked.
+ * When that callback returns @task will be freed,
+ * so @task must not be referenced after this
+ * method completes.
+ */
+void qio_task_wait_thread(QIOTask *task);
+
+
+/**
+ * qio_task_complete:
+ * @task: the task struct
+ *
+ * Invoke the completion callback for @task and
+ * then free its memory.
+ */
+void qio_task_complete(QIOTask *task);
+
+
+/**
+ * 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
+ * @result: pointer to the result data
+ *
+ * Associate an opaque result with the task,
+ * which can later be retrieved with the
+ * qio_task_get_result_pointer() method
+ *
+ */
+void qio_task_set_result_pointer(QIOTask *task,
+                                 gpointer result,
+                                 GDestroyNotify notify);
+
+
+/**
+ * qio_task_get_result_pointer:
+ * @task: the task struct
+ *
+ * Retrieve the opaque result data associated
+ * with the task, if any.
+ *
+ * Returns: the task result, or NULL
+ */
+gpointer qio_task_get_result_pointer(QIOTask *task);
+
+
+/**
+ * qio_task_get_source:
+ * @task: the task struct
+ *
+ * Get the source object associated with the background
+ * task. The caller does not own a reference on the
+ * returned Object, and so should call object_ref()
+ * if it wants to keep the object pointer outside the
+ * lifetime of the QIOTask object.
+ *
+ * Returns: the source object
+ */
+Object *qio_task_get_source(QIOTask *task);
+
+#endif /* QIO_TASK_H */