1 files changed, 116 insertions, 0 deletions
diff --git a/xlators/features/qemu-block/src/coroutine-synctask.c b/xlators/features/qemu-block/src/coroutine-synctask.c
new file mode 100644
index 000000000..e43988a95
--- /dev/null
+++ b/xlators/features/qemu-block/src/coroutine-synctask.c
@@ -0,0 +1,116 @@
+/*
+  Copyright (c) 2013 Red Hat, Inc. <http://www.redhat.com>
+  This file is part of GlusterFS.
+
+  This file is licensed to you under your choice of the GNU Lesser
+  General Public License, version 3 or any later version (LGPLv3 or
+  later), or the GNU General Public License, version 2 (GPLv2), in all
+  cases as published by the Free Software Foundation.
+*/
+
+
+#ifndef _CONFIG_H
+#define _CONFIG_H
+#include "config.h"
+#endif
+
+#include "glusterfs.h"
+#include "logging.h"
+#include "dict.h"
+#include "xlator.h"
+#include "syncop.h"
+#include "qemu-block-memory-types.h"
+
+#include "qemu-block.h"
+
+/*
+ * This code serves as the bridge from the main glusterfs context to the qemu
+ * coroutine context via synctask. We create a single threaded syncenv with a
+ * single synctask responsible for processing a queue of coroutines. The qemu
+ * code invoked from within the synctask function handlers uses the ucontext
+ * coroutine implementation and scheduling logic internal to qemu. This
+ * effectively donates a thread of execution to qemu and its internal coroutine
+ * management.
+ *
+ * NOTE: The existence of concurrent synctasks has proven quite racy with regard
+ * to qemu coroutine management, particularly related to the lifecycle
+ * differences with top-level synctasks and internally created coroutines and
+ * interactions with qemu-internal queues (and locks, in turn). We explicitly
+ * disallow this scenario, via the queue, until it is more well supported.
+ */
+
+static struct {
+	struct list_head	queue;
+	gf_lock_t		lock;
+	struct synctask		*task;
+} qb_co;
+
+static void
+init_qbco()
+{
+	INIT_LIST_HEAD(&qb_co.queue);
+	LOCK_INIT(&qb_co.lock);
+}
+
+static int
+synctask_nop_cbk (int ret, call_frame_t *frame, void *opaque)
+{
+	return 0;
+}
+
+static int
+qb_synctask_wrap (void *opaque)
+{
+	qb_local_t *qb_local, *tmp;
+
+	LOCK(&qb_co.lock);
+
+	while (!list_empty(&qb_co.queue)) {
+		list_for_each_entry_safe(qb_local, tmp, &qb_co.queue, list) {
+			list_del_init(&qb_local->list);
+			break;
+		}
+
+		UNLOCK(&qb_co.lock);
+
+		qb_local->synctask_fn(qb_local);
+		/* qb_local is now unwound and gone! */
+
+		LOCK(&qb_co.lock);
+	}
+
+	qb_co.task = NULL;
+
+	UNLOCK(&qb_co.lock);
+
+	return 0;
+}
+
+int
+qb_coroutine (call_frame_t *frame, synctask_fn_t fn)
+{
+	qb_local_t *qb_local = NULL;
+	qb_conf_t *qb_conf = NULL;
+	static int init = 0;
+
+	qb_local = frame->local;
+	qb_local->synctask_fn = fn;
+	qb_conf = frame->this->private;
+
+	if (!init) {
+		init = 1;
+		init_qbco();
+	}
+
+	LOCK(&qb_co.lock);
+
+	if (!qb_co.task)
+		qb_co.task = synctask_create(qb_conf->env, qb_synctask_wrap,
+					     synctask_nop_cbk, frame, NULL);
+
+	list_add_tail(&qb_local->list, &qb_co.queue);
+
+	UNLOCK(&qb_co.lock);
+
+	return 0;
+}