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diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
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+/*
+ * AioContext wait support
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef QEMU_AIO_WAIT_H
+#define QEMU_AIO_WAIT_H
+
+#include "block/aio.h"
+
+/**
+ * AioWait:
+ *
+ * An object that facilitates synchronous waiting on a condition.  The main
+ * loop can wait on an operation running in an IOThread as follows:
+ *
+ *   AioWait *wait = ...;
+ *   AioContext *ctx = ...;
+ *   MyWork work = { .done = false };
+ *   schedule_my_work_in_iothread(ctx, &work);
+ *   AIO_WAIT_WHILE(wait, ctx, !work.done);
+ *
+ * The IOThread must call aio_wait_kick() to notify the main loop when
+ * work.done changes:
+ *
+ *   static void do_work(...)
+ *   {
+ *       ...
+ *       work.done = true;
+ *       aio_wait_kick(wait);
+ *   }
+ */
+typedef struct {
+    /* Is the main loop waiting for a kick?  Accessed with atomic ops. */
+    bool need_kick;
+} AioWait;
+
+/**
+ * AIO_WAIT_WHILE:
+ * @wait: the aio wait object
+ * @ctx: the aio context
+ * @cond: wait while this conditional expression is true
+ *
+ * Wait while a condition is true.  Use this to implement synchronous
+ * operations that require event loop activity.
+ *
+ * The caller must be sure that something calls aio_wait_kick() when the value
+ * of @cond might have changed.
+ *
+ * The caller's thread must be the IOThread that owns @ctx or the main loop
+ * thread (with @ctx acquired exactly once).  This function cannot be used to
+ * wait on conditions between two IOThreads since that could lead to deadlock,
+ * go via the main loop instead.
+ */
+#define AIO_WAIT_WHILE(wait, ctx, cond) ({                  \
+    bool waited_ = false;                                   \
+    bool busy_ = true;                                      \
+    AioWait *wait_ = (wait);                                \
+    AioContext *ctx_ = (ctx);                               \
+    if (in_aio_context_home_thread(ctx_)) {                 \
+        while ((cond) || busy_) {                           \
+            busy_ = aio_poll(ctx_, (cond));                 \
+            waited_ |= !!(cond) | busy_;                    \
+        }                                                   \
+    } else {                                                \
+        assert(qemu_get_current_aio_context() ==            \
+               qemu_get_aio_context());                     \
+        assert(!wait_->need_kick);                          \
+        /* Set wait_->need_kick before evaluating cond.  */ \
+        atomic_mb_set(&wait_->need_kick, true);             \
+        while (busy_) {                                     \
+            if ((cond)) {                                   \
+                waited_ = busy_ = true;                     \
+                aio_context_release(ctx_);                  \
+                aio_poll(qemu_get_aio_context(), true);     \
+                aio_context_acquire(ctx_);                  \
+            } else {                                        \
+                busy_ = aio_poll(ctx_, false);              \
+                waited_ |= busy_;                           \
+            }                                               \
+        }                                                   \
+        atomic_set(&wait_->need_kick, false);               \
+    }                                                       \
+    waited_; })
+
+/**
+ * aio_wait_kick:
+ * @wait: the aio wait object that should re-evaluate its condition
+ *
+ * Wake up the main thread if it is waiting on AIO_WAIT_WHILE().  During
+ * synchronous operations performed in an IOThread, the main thread lets the
+ * IOThread's event loop run, waiting for the operation to complete.  A
+ * aio_wait_kick() call will wake up the main thread.
+ */
+void aio_wait_kick(AioWait *wait);
+
+#endif /* QEMU_AIO_WAIT */