[RFC,05/12] coroutine: Add coroutines

diff --git a/Makefile.objs b/Makefile.objs
index ae26396..7933fc9 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -15,7 +15,7 @@  oslib-obj-$(CONFIG_POSIX) += oslib-posix.o
 
 block-obj-y = cutils.o cache-utils.o qemu-malloc.o qemu-option.o module.o
 block-obj-y += nbd.o block.o aio.o aes.o qemu-config.o
-block-obj-$(CONFIG_POSIX) += posix-aio-compat.o continuation.o coroutine_ucontext.o
+block-obj-$(CONFIG_POSIX) += posix-aio-compat.o continuation.o coroutine_ucontext.o qemu-coroutine.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
 
 block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
diff --git a/qemu-coroutine.c b/qemu-coroutine.c
new file mode 100644
index 0000000..dd2cd8e
--- /dev/null
+++ b/qemu-coroutine.c
@@ -0,0 +1,40 @@ 
+/*
+ * QEMU coroutines
+ *
+ * Copyright IBM, Corp. 2011
+ *
+ * Authors:
+ *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include "coroutine.h"
+
+#include "qemu-common.h"
+#include "qemu-coroutine.h"
+
+struct Coroutine {
+    struct coroutine co;
+};
+
+Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
+{
+    Coroutine *coroutine = qemu_mallocz(sizeof(*coroutine));
+
+    coroutine->co.entry = entry;
+    coroutine_init(&coroutine->co);
+    return coroutine;
+}
+
+void *qemu_coroutine_enter(Coroutine *coroutine, void *opaque)
+{
+    return coroutine_yieldto(&coroutine->co, opaque);
+}
+
+void * coroutine_fn qemu_coroutine_yield(void *opaque)
+{
+    return coroutine_yield(opaque);
+}
diff --git a/qemu-coroutine.h b/qemu-coroutine.h
new file mode 100644
index 0000000..22fe4ea
--- /dev/null
+++ b/qemu-coroutine.h
@@ -0,0 +1,76 @@ 
+/*
+ * QEMU coroutine implementation
+ *
+ * Copyright IBM, Corp. 2011
+ *
+ * Authors:
+ *  Stefan Hajnoczi    <stefanha@linux.vnet.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_COROUTINE_H
+#define QEMU_COROUTINE_H
+
+/**
+ * Mark a function that executes in coroutine context
+ *
+ * Functions that execute in coroutine context cannot be called directly from
+ * normal functions.  In the future it would be nice to enable compiler or
+ * static checker support for catching such errors.  This annotation might make
+ * it possible and in the meantime it serves as documentation.
+ *
+ * For example:
+ *
+ *   static void coroutine_fn foo(void) {
+ *       ....
+ *   }
+ */
+#define coroutine_fn
+
+typedef struct Coroutine Coroutine;
+
+/**
+ * Coroutine entry point
+ *
+ * When the coroutine is entered for the first time, opaque is passed in as an
+ * argument.
+ *
+ * When this function returns, the coroutine is destroyed automatically and the
+ * return value is passed back to the caller who last entered the coroutine.
+ */
+typedef void * coroutine_fn CoroutineEntry(void *opaque);
+
+/**
+ * Create a new coroutine
+ *
+ * Use qemu_coroutine_enter() to actually transfer control to the coroutine.
+ */
+Coroutine *qemu_coroutine_create(CoroutineEntry *entry);
+
+/**
+ * Transfer control to a coroutine
+ *
+ * The opaque argument is made available to the coroutine either as the entry
+ * function argument if this is the first time a new coroutine is entered, or
+ * as the return value from qemu_coroutine_yield().
+ *
+ * The return value from this function is either an opaque value yielded by the
+ * coroutine or the coroutine entry function return value when the coroutine
+ * terminates.
+ */
+void *qemu_coroutine_enter(Coroutine *coroutine, void *opaque);
+
+/**
+ * Transfer control back to a coroutine's caller
+ *
+ * The opaque argument is returned from the calling qemu_coroutine_enter().
+ *
+ * The return value is the argument passed back in from the next
+ * qemu_coroutine_enter().
+ */
+void * coroutine_fn qemu_coroutine_yield(void *opaque);
+
+#endif /* QEMU_COROUTINE_H */