nbd/client-connection.c - qemu - Git at Google

 /*
  * QEMU Block driver for  NBD
  *
  * Copyright (c) 2021 Virtuozzo International GmbH.
  *
  * 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.
  */

 #include "qemu/osdep.h"
 #include "trace.h"

 #include "block/nbd.h"

 #include "qapi/qapi-visit-sockets.h"
 #include "qapi/clone-visitor.h"

 struct NBDClientConnection {
     /* Initialization constants, never change */
     SocketAddress *saddr; /* address to connect to */
     QCryptoTLSCreds *tlscreds;
     char *tlshostname;
     NBDExportInfo initial_info;
     bool do_negotiation;
     bool do_retry;

     QemuMutex mutex;

     NBDExportInfo updated_info;
     /*
      * @sioc represents a successful result. While thread is running, @sioc is
      * used only by thread and not protected by mutex. When thread is not
      * running, @sioc is stolen by nbd_co_establish_connection() under mutex.
      */
     QIOChannelSocket *sioc;
     QIOChannel *ioc;
     /*
      * @err represents previous attempt. It may be copied by
      * nbd_co_establish_connection() when it reports failure.
      */
     Error *err;

     /* All further fields are accessed only under mutex */
     bool running; /* thread is running now */
     bool detached; /* thread is detached and should cleanup the state */

     /*
      * wait_co: if non-NULL, which coroutine to wake in
      * nbd_co_establish_connection() after yield()
      */
     Coroutine *wait_co;
 };

 /*
  * The function isn't protected by any mutex, only call it when the client
  * connection attempt has not yet started.
  */
 void nbd_client_connection_enable_retry(NBDClientConnection *conn)
 {
     conn->do_retry = true;
 }

 NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
                                                bool do_negotiation,
                                                const char *export_name,
                                                const char *x_dirty_bitmap,
                                                QCryptoTLSCreds *tlscreds,
                                                const char *tlshostname)
 {
     NBDClientConnection *conn = g_new(NBDClientConnection, 1);

     object_ref(OBJECT(tlscreds));
     *conn = (NBDClientConnection) {
         .saddr = QAPI_CLONE(SocketAddress, saddr),
         .tlscreds = tlscreds,
         .tlshostname = g_strdup(tlshostname),
         .do_negotiation = do_negotiation,

         .initial_info.request_sizes = true,
         .initial_info.structured_reply = true,
         .initial_info.base_allocation = true,
         .initial_info.x_dirty_bitmap = g_strdup(x_dirty_bitmap),
         .initial_info.name = g_strdup(export_name ?: "")
     };

     qemu_mutex_init(&conn->mutex);

     return conn;
 }

 static void nbd_client_connection_do_free(NBDClientConnection *conn)
 {
     if (conn->sioc) {
         qio_channel_close(QIO_CHANNEL(conn->sioc), NULL);
         object_unref(OBJECT(conn->sioc));
     }
     error_free(conn->err);
     qapi_free_SocketAddress(conn->saddr);
     g_free(conn->tlshostname);
     object_unref(OBJECT(conn->tlscreds));
     g_free(conn->initial_info.x_dirty_bitmap);
     g_free(conn->initial_info.name);
     g_free(conn);
 }

 /*
  * Connect to @addr and do NBD negotiation if @info is not null. If @tlscreds
  * are given @outioc is returned. @outioc is provided only on success.  The call
  * may be cancelled from other thread by simply qio_channel_shutdown(sioc).
  */
 static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
                        NBDExportInfo *info, QCryptoTLSCreds *tlscreds,
                        const char *tlshostname,
                        QIOChannel **outioc, Error **errp)
 {
     int ret;

     if (outioc) {
         *outioc = NULL;
     }

     ret = qio_channel_socket_connect_sync(sioc, addr, errp);
     if (ret < 0) {
         return ret;
     }

     qio_channel_set_delay(QIO_CHANNEL(sioc), false);

     if (!info) {
         return 0;
     }

     ret = nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc), tlscreds,
                                 tlshostname,
                                 outioc, info, errp);
     if (ret < 0) {
         /*
          * nbd_receive_negotiate() may setup tls ioc and return it even on
          * failure path. In this case we should use it instead of original
          * channel.
          */
         if (outioc && *outioc) {
             qio_channel_close(QIO_CHANNEL(*outioc), NULL);
             object_unref(OBJECT(*outioc));
             *outioc = NULL;
         } else {
             qio_channel_close(QIO_CHANNEL(sioc), NULL);
         }

         return ret;
     }

     return 0;
 }

 static void *connect_thread_func(void *opaque)
 {
     NBDClientConnection *conn = opaque;
     int ret;
     bool do_free;
     uint64_t timeout = 1;
     uint64_t max_timeout = 16;

     qemu_mutex_lock(&conn->mutex);
     while (!conn->detached) {
         Error *local_err = NULL;

         assert(!conn->sioc);
         conn->sioc = qio_channel_socket_new();

         qemu_mutex_unlock(&conn->mutex);

         conn->updated_info = conn->initial_info;

         ret = nbd_connect(conn->sioc, conn->saddr,
                           conn->do_negotiation ? &conn->updated_info : NULL,
                           conn->tlscreds, conn->tlshostname,
                           &conn->ioc, &local_err);

         /*
          * conn->updated_info will finally be returned to the user. Clear the
          * pointers to our internally allocated strings, which are IN parameters
          * of nbd_receive_negotiate() and therefore nbd_connect(). Caller
          * shoudn't be interested in these fields.
          */
         conn->updated_info.x_dirty_bitmap = NULL;
         conn->updated_info.name = NULL;

         qemu_mutex_lock(&conn->mutex);

         error_free(conn->err);
         conn->err = NULL;
         error_propagate(&conn->err, local_err);

         if (ret < 0) {
             object_unref(OBJECT(conn->sioc));
             conn->sioc = NULL;
             if (conn->do_retry && !conn->detached) {
                 trace_nbd_connect_thread_sleep(timeout);
                 qemu_mutex_unlock(&conn->mutex);

                 sleep(timeout);
                 if (timeout < max_timeout) {
                     timeout *= 2;
                 }

                 qemu_mutex_lock(&conn->mutex);
                 continue;
             }
         }

         break;
     }

     /* mutex is locked */

     assert(conn->running);
     conn->running = false;
     if (conn->wait_co) {
         aio_co_wake(conn->wait_co);
         conn->wait_co = NULL;
     }
     do_free = conn->detached;

     qemu_mutex_unlock(&conn->mutex);

     if (do_free) {
         nbd_client_connection_do_free(conn);
     }

     return NULL;
 }

 void nbd_client_connection_release(NBDClientConnection *conn)
 {
     bool do_free = false;

     if (!conn) {
         return;
     }

     WITH_QEMU_LOCK_GUARD(&conn->mutex) {
         assert(!conn->detached);
         if (conn->running) {
             conn->detached = true;
         } else {
             do_free = true;
         }
         if (conn->sioc) {
             qio_channel_shutdown(QIO_CHANNEL(conn->sioc),
                                  QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
         }
     }

     if (do_free) {
         nbd_client_connection_do_free(conn);
     }
 }

 /*
  * Get a new connection in context of @conn:
  *   if the thread is running, wait for completion
  *   if the thread already succeeded in the background, and user didn't get the
  *     result, just return it now
  *   otherwise the thread is not running, so start a thread and wait for
  *     completion
  *
  * If @blocking is false, don't wait for the thread, return immediately.
  *
  * If @info is not NULL, also do nbd-negotiation after successful connection.
  * In this case info is used only as out parameter, and is fully initialized by
  * nbd_co_establish_connection(). "IN" fields of info as well as related only to
  * nbd_receive_export_list() would be zero (see description of NBDExportInfo in
  * include/block/nbd.h).
  */
 QIOChannel *coroutine_fn
 nbd_co_establish_connection(NBDClientConnection *conn, NBDExportInfo *info,
                             bool blocking, Error **errp)
 {
     QemuThread thread;

     if (conn->do_negotiation) {
         assert(info);
     }

     WITH_QEMU_LOCK_GUARD(&conn->mutex) {
         /*
          * Don't call nbd_co_establish_connection() in several coroutines in
          * parallel. Only one call at once is supported.
          */
         assert(!conn->wait_co);

         if (!conn->running) {
             if (conn->sioc) {
                 /* Previous attempt finally succeeded in background */
                 if (conn->do_negotiation) {
                     memcpy(info, &conn->updated_info, sizeof(*info));
                     if (conn->ioc) {
                         /* TLS channel now has own reference to parent */
                         object_unref(OBJECT(conn->sioc));
                         conn->sioc = NULL;

                         return g_steal_pointer(&conn->ioc);
                     }
                 }

                 assert(!conn->ioc);

                 return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
             }

             conn->running = true;
             qemu_thread_create(&thread, "nbd-connect",
                                connect_thread_func, conn, QEMU_THREAD_DETACHED);
         }

         if (!blocking) {
             if (conn->err) {
                 error_propagate(errp, error_copy(conn->err));
             } else {
                 error_setg(errp, "No connection at the moment");
             }

             return NULL;
         }

         conn->wait_co = qemu_coroutine_self();
     }

     /*
      * We are going to wait for connect-thread finish, but
      * nbd_co_establish_connection_cancel() can interrupt.
      */
     qemu_coroutine_yield();

     WITH_QEMU_LOCK_GUARD(&conn->mutex) {
         if (conn->running) {
             /*
              * The connection attempt was canceled and the coroutine resumed
              * before the connection thread finished its job.  Report the
              * attempt as failed, but leave the connection thread running,
              * to reuse it for the next connection attempt.
              */
             if (conn->err) {
                 error_propagate(errp, error_copy(conn->err));
             } else {
                 /*
                  * The only possible case here is cancelling by open_timer
                  * during nbd_open(). So, the error message is for that case.
                  * If we have more use cases, we can refactor
                  * nbd_co_establish_connection_cancel() to take an additional
                  * parameter cancel_reason, that would be passed than to the
                  * caller of cancelled nbd_co_establish_connection().
                  */
                 error_setg(errp, "Connection attempt cancelled by timeout");
             }

             return NULL;
         } else {
             /* Thread finished. There must be either error or sioc */
             assert(!conn->err != !conn->sioc);

             if (conn->err) {
                 error_propagate(errp, error_copy(conn->err));
                 return NULL;
             }

             if (conn->do_negotiation) {
                 memcpy(info, &conn->updated_info, sizeof(*info));
                 if (conn->ioc) {
                     /* TLS channel now has own reference to parent */
                     object_unref(OBJECT(conn->sioc));
                     conn->sioc = NULL;

                     return g_steal_pointer(&conn->ioc);
                 }
             }

             assert(!conn->ioc);

             return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
         }
     }

     abort(); /* unreachable */
 }

 /*
  * nbd_co_establish_connection_cancel
  * Cancel nbd_co_establish_connection() asynchronously.
  *
  * Note that this function neither directly stops the thread nor closes the
  * socket, but rather safely wakes nbd_co_establish_connection() which is
  * sleeping in yield()
  */
 void nbd_co_establish_connection_cancel(NBDClientConnection *conn)
 {
     Coroutine *wait_co;

     WITH_QEMU_LOCK_GUARD(&conn->mutex) {
         wait_co = g_steal_pointer(&conn->wait_co);
     }

     if (wait_co) {
         aio_co_wake(wait_co);
     }
 }
	/*
	* QEMU Block driver for NBD
	*
	* Copyright (c) 2021 Virtuozzo International GmbH.
	*
	* 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.
	*/

	#include "qemu/osdep.h"
	#include "trace.h"

	#include "block/nbd.h"

	#include "qapi/qapi-visit-sockets.h"
	#include "qapi/clone-visitor.h"

	struct NBDClientConnection {
	/* Initialization constants, never change */
	SocketAddress saddr; / address to connect to */
	QCryptoTLSCreds *tlscreds;
	char *tlshostname;
	NBDExportInfo initial_info;
	bool do_negotiation;
	bool do_retry;

	QemuMutex mutex;

	NBDExportInfo updated_info;
	/*
	* @sioc represents a successful result. While thread is running, @sioc is
	* used only by thread and not protected by mutex. When thread is not
	* running, @sioc is stolen by nbd_co_establish_connection() under mutex.
	*/
	QIOChannelSocket *sioc;
	QIOChannel *ioc;
	/*
	* @err represents previous attempt. It may be copied by
	* nbd_co_establish_connection() when it reports failure.
	*/
	Error *err;

	/* All further fields are accessed only under mutex */
	bool running; /* thread is running now */
	bool detached; /* thread is detached and should cleanup the state */

	/*
	* wait_co: if non-NULL, which coroutine to wake in
	* nbd_co_establish_connection() after yield()
	*/
	Coroutine *wait_co;
	};

	/*
	* The function isn't protected by any mutex, only call it when the client
	* connection attempt has not yet started.
	*/
	void nbd_client_connection_enable_retry(NBDClientConnection *conn)
	{
	conn->do_retry = true;
	}

	NBDClientConnection nbd_client_connection_new(const SocketAddress saddr,
	bool do_negotiation,
	const char *export_name,
	const char *x_dirty_bitmap,
	QCryptoTLSCreds *tlscreds,
	const char *tlshostname)
	{
	NBDClientConnection *conn = g_new(NBDClientConnection, 1);

	object_ref(OBJECT(tlscreds));
	*conn = (NBDClientConnection) {
	.saddr = QAPI_CLONE(SocketAddress, saddr),
	.tlscreds = tlscreds,
	.tlshostname = g_strdup(tlshostname),
	.do_negotiation = do_negotiation,

	.initial_info.request_sizes = true,
	.initial_info.structured_reply = true,
	.initial_info.base_allocation = true,
	.initial_info.x_dirty_bitmap = g_strdup(x_dirty_bitmap),
	.initial_info.name = g_strdup(export_name ?: "")
	};

	qemu_mutex_init(&conn->mutex);

	return conn;
	}

	static void nbd_client_connection_do_free(NBDClientConnection *conn)
	{
	if (conn->sioc) {
	qio_channel_close(QIO_CHANNEL(conn->sioc), NULL);
	object_unref(OBJECT(conn->sioc));
	}
	error_free(conn->err);
	qapi_free_SocketAddress(conn->saddr);
	g_free(conn->tlshostname);
	object_unref(OBJECT(conn->tlscreds));
	g_free(conn->initial_info.x_dirty_bitmap);
	g_free(conn->initial_info.name);
	g_free(conn);
	}

	/*
	* Connect to @addr and do NBD negotiation if @info is not null. If @tlscreds
	* are given @outioc is returned. @outioc is provided only on success. The call
	* may be cancelled from other thread by simply qio_channel_shutdown(sioc).
	*/
	static int nbd_connect(QIOChannelSocket sioc, SocketAddress addr,
	NBDExportInfo info, QCryptoTLSCreds tlscreds,
	const char *tlshostname,
	QIOChannel outioc, Error errp)
	{
	int ret;

	if (outioc) {
	*outioc = NULL;
	}

	ret = qio_channel_socket_connect_sync(sioc, addr, errp);
	if (ret < 0) {
	return ret;
	}

	qio_channel_set_delay(QIO_CHANNEL(sioc), false);

	if (!info) {
	return 0;
	}

	ret = nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc), tlscreds,
	tlshostname,
	outioc, info, errp);
	if (ret < 0) {
	/*
	* nbd_receive_negotiate() may setup tls ioc and return it even on
	* failure path. In this case we should use it instead of original
	* channel.
	*/
	if (outioc && *outioc) {
	qio_channel_close(QIO_CHANNEL(*outioc), NULL);
	object_unref(OBJECT(*outioc));
	*outioc = NULL;
	} else {
	qio_channel_close(QIO_CHANNEL(sioc), NULL);
	}

	return ret;
	}

	return 0;
	}

	static void connect_thread_func(void opaque)
	{
	NBDClientConnection *conn = opaque;
	int ret;
	bool do_free;
	uint64_t timeout = 1;
	uint64_t max_timeout = 16;

	qemu_mutex_lock(&conn->mutex);
	while (!conn->detached) {
	Error *local_err = NULL;

	assert(!conn->sioc);
	conn->sioc = qio_channel_socket_new();

	qemu_mutex_unlock(&conn->mutex);

	conn->updated_info = conn->initial_info;

	ret = nbd_connect(conn->sioc, conn->saddr,
	conn->do_negotiation ? &conn->updated_info : NULL,
	conn->tlscreds, conn->tlshostname,
	&conn->ioc, &local_err);

	/*
	* conn->updated_info will finally be returned to the user. Clear the
	* pointers to our internally allocated strings, which are IN parameters
	* of nbd_receive_negotiate() and therefore nbd_connect(). Caller
	* shoudn't be interested in these fields.
	*/
	conn->updated_info.x_dirty_bitmap = NULL;
	conn->updated_info.name = NULL;

	qemu_mutex_lock(&conn->mutex);

	error_free(conn->err);
	conn->err = NULL;
	error_propagate(&conn->err, local_err);

	if (ret < 0) {
	object_unref(OBJECT(conn->sioc));
	conn->sioc = NULL;
	if (conn->do_retry && !conn->detached) {
	trace_nbd_connect_thread_sleep(timeout);
	qemu_mutex_unlock(&conn->mutex);

	sleep(timeout);
	if (timeout < max_timeout) {
	timeout *= 2;
	}

	qemu_mutex_lock(&conn->mutex);
	continue;
	}
	}

	break;
	}

	/* mutex is locked */

	assert(conn->running);
	conn->running = false;
	if (conn->wait_co) {
	aio_co_wake(conn->wait_co);
	conn->wait_co = NULL;
	}
	do_free = conn->detached;

	qemu_mutex_unlock(&conn->mutex);

	if (do_free) {
	nbd_client_connection_do_free(conn);
	}

	return NULL;
	}

	void nbd_client_connection_release(NBDClientConnection *conn)
	{
	bool do_free = false;

	if (!conn) {
	return;
	}

	WITH_QEMU_LOCK_GUARD(&conn->mutex) {
	assert(!conn->detached);
	if (conn->running) {
	conn->detached = true;
	} else {
	do_free = true;
	}
	if (conn->sioc) {
	qio_channel_shutdown(QIO_CHANNEL(conn->sioc),
	QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
	}
	}

	if (do_free) {
	nbd_client_connection_do_free(conn);
	}
	}

	/*
	* Get a new connection in context of @conn:
	* if the thread is running, wait for completion
	* if the thread already succeeded in the background, and user didn't get the
	* result, just return it now
	* otherwise the thread is not running, so start a thread and wait for
	* completion
	*
	* If @blocking is false, don't wait for the thread, return immediately.
	*
	* If @info is not NULL, also do nbd-negotiation after successful connection.
	* In this case info is used only as out parameter, and is fully initialized by
	* nbd_co_establish_connection(). "IN" fields of info as well as related only to
	* nbd_receive_export_list() would be zero (see description of NBDExportInfo in
	* include/block/nbd.h).
	*/
	QIOChannel *coroutine_fn
	nbd_co_establish_connection(NBDClientConnection conn, NBDExportInfo info,
	bool blocking, Error **errp)
	{
	QemuThread thread;

	if (conn->do_negotiation) {
	assert(info);
	}

	WITH_QEMU_LOCK_GUARD(&conn->mutex) {
	/*
	* Don't call nbd_co_establish_connection() in several coroutines in
	* parallel. Only one call at once is supported.
	*/
	assert(!conn->wait_co);

	if (!conn->running) {
	if (conn->sioc) {
	/* Previous attempt finally succeeded in background */
	if (conn->do_negotiation) {
	memcpy(info, &conn->updated_info, sizeof(*info));
	if (conn->ioc) {
	/* TLS channel now has own reference to parent */
	object_unref(OBJECT(conn->sioc));
	conn->sioc = NULL;

	return g_steal_pointer(&conn->ioc);
	}
	}

	assert(!conn->ioc);

	return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
	}

	conn->running = true;
	qemu_thread_create(&thread, "nbd-connect",
	connect_thread_func, conn, QEMU_THREAD_DETACHED);
	}

	if (!blocking) {
	if (conn->err) {
	error_propagate(errp, error_copy(conn->err));
	} else {
	error_setg(errp, "No connection at the moment");
	}

	return NULL;
	}

	conn->wait_co = qemu_coroutine_self();
	}

	/*
	* We are going to wait for connect-thread finish, but
	* nbd_co_establish_connection_cancel() can interrupt.
	*/
	qemu_coroutine_yield();

	WITH_QEMU_LOCK_GUARD(&conn->mutex) {
	if (conn->running) {
	/*
	* The connection attempt was canceled and the coroutine resumed
	* before the connection thread finished its job. Report the
	* attempt as failed, but leave the connection thread running,
	* to reuse it for the next connection attempt.
	*/
	if (conn->err) {
	error_propagate(errp, error_copy(conn->err));
	} else {
	/*
	* The only possible case here is cancelling by open_timer
	* during nbd_open(). So, the error message is for that case.
	* If we have more use cases, we can refactor
	* nbd_co_establish_connection_cancel() to take an additional
	* parameter cancel_reason, that would be passed than to the
	* caller of cancelled nbd_co_establish_connection().
	*/
	error_setg(errp, "Connection attempt cancelled by timeout");
	}

	return NULL;
	} else {
	/* Thread finished. There must be either error or sioc */
	assert(!conn->err != !conn->sioc);

	if (conn->err) {
	error_propagate(errp, error_copy(conn->err));
	return NULL;
	}

	if (conn->do_negotiation) {
	memcpy(info, &conn->updated_info, sizeof(*info));
	if (conn->ioc) {
	/* TLS channel now has own reference to parent */
	object_unref(OBJECT(conn->sioc));
	conn->sioc = NULL;

	return g_steal_pointer(&conn->ioc);
	}
	}

	assert(!conn->ioc);

	return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
	}
	}

	abort(); /* unreachable */
	}

	/*
	* nbd_co_establish_connection_cancel
	* Cancel nbd_co_establish_connection() asynchronously.
	*
	* Note that this function neither directly stops the thread nor closes the
	* socket, but rather safely wakes nbd_co_establish_connection() which is
	* sleeping in yield()
	*/
	void nbd_co_establish_connection_cancel(NBDClientConnection *conn)
	{
	Coroutine *wait_co;

	WITH_QEMU_LOCK_GUARD(&conn->mutex) {
	wait_co = g_steal_pointer(&conn->wait_co);
	}

	if (wait_co) {
	aio_co_wake(wait_co);
	}
	}