util/vhost-user-server.c - qemu - Git at Google

 /*
  * Sharing QEMU devices via vhost-user protocol
  *
  * Copyright (c) Coiby Xu <coiby.xu@gmail.com>.
  * Copyright (c) 2020 Red Hat, Inc.
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or
  * later.  See the COPYING file in the top-level directory.
  */
 #include "qemu/osdep.h"
 #include "qemu/main-loop.h"
 #include "qemu/vhost-user-server.h"
 #include "block/aio-wait.h"

 /*
  * Theory of operation:
  *
  * VuServer is started and stopped by vhost_user_server_start() and
  * vhost_user_server_stop() from the main loop thread. Starting the server
  * opens a vhost-user UNIX domain socket and listens for incoming connections.
  * Only one connection is allowed at a time.
  *
  * The connection is handled by the vu_client_trip() coroutine in the
  * VuServer->ctx AioContext. The coroutine consists of a vu_dispatch() loop
  * where libvhost-user calls vu_message_read() to receive the next vhost-user
  * protocol messages over the UNIX domain socket.
  *
  * When virtqueues are set up libvhost-user calls set_watch() to monitor kick
  * fds. These fds are also handled in the VuServer->ctx AioContext.
  *
  * Both vu_client_trip() and kick fd monitoring can be stopped by shutting down
  * the socket connection. Shutting down the socket connection causes
  * vu_message_read() to fail since no more data can be received from the socket.
  * After vu_dispatch() fails, vu_client_trip() calls vu_deinit() to stop
  * libvhost-user before terminating the coroutine. vu_deinit() calls
  * remove_watch() to stop monitoring kick fds and this stops virtqueue
  * processing.
  *
  * When vu_client_trip() has finished cleaning up it schedules a BH in the main
  * loop thread to accept the next client connection.
  *
  * When libvhost-user detects an error it calls panic_cb() and sets the
  * dev->broken flag. Both vu_client_trip() and kick fd processing stop when
  * the dev->broken flag is set.
  *
  * It is possible to switch AioContexts using
  * vhost_user_server_detach_aio_context() and
  * vhost_user_server_attach_aio_context(). They stop monitoring fds in the old
  * AioContext and resume monitoring in the new AioContext. The vu_client_trip()
  * coroutine remains in a yielded state during the switch. This is made
  * possible by QIOChannel's support for spurious coroutine re-entry in
  * qio_channel_yield(). The coroutine will restart I/O when re-entered from the
  * new AioContext.
  */

 static void vmsg_close_fds(VhostUserMsg *vmsg)
 {
     int i;
     for (i = 0; i < vmsg->fd_num; i++) {
         close(vmsg->fds[i]);
     }
 }

 static void vmsg_unblock_fds(VhostUserMsg *vmsg)
 {
     int i;
     for (i = 0; i < vmsg->fd_num; i++) {
         qemu_set_nonblock(vmsg->fds[i]);
     }
 }

 static void panic_cb(VuDev *vu_dev, const char *buf)
 {
     error_report("vu_panic: %s", buf);
 }

 static bool coroutine_fn
 vu_message_read(VuDev *vu_dev, int conn_fd, VhostUserMsg *vmsg)
 {
     struct iovec iov = {
         .iov_base = (char *)vmsg,
         .iov_len = VHOST_USER_HDR_SIZE,
     };
     int rc, read_bytes = 0;
     Error *local_err = NULL;
     const size_t max_fds = G_N_ELEMENTS(vmsg->fds);
     VuServer *server = container_of(vu_dev, VuServer, vu_dev);
     QIOChannel *ioc = server->ioc;

     vmsg->fd_num = 0;
     if (!ioc) {
         error_report_err(local_err);
         goto fail;
     }

     assert(qemu_in_coroutine());
     do {
         size_t nfds = 0;
         int *fds = NULL;

         /*
          * qio_channel_readv_full may have short reads, keeping calling it
          * until getting VHOST_USER_HDR_SIZE or 0 bytes in total
          */
         rc = qio_channel_readv_full(ioc, &iov, 1, &fds, &nfds, &local_err);
         if (rc < 0) {
             if (rc == QIO_CHANNEL_ERR_BLOCK) {
                 assert(local_err == NULL);
                 qio_channel_yield(ioc, G_IO_IN);
                 continue;
             } else {
                 error_report_err(local_err);
                 goto fail;
             }
         }

         if (nfds > 0) {
             if (vmsg->fd_num + nfds > max_fds) {
                 error_report("A maximum of %zu fds are allowed, "
                              "however got %zu fds now",
                              max_fds, vmsg->fd_num + nfds);
                 g_free(fds);
                 goto fail;
             }
             memcpy(vmsg->fds + vmsg->fd_num, fds, nfds * sizeof(vmsg->fds[0]));
             vmsg->fd_num += nfds;
             g_free(fds);
         }

         if (rc == 0) { /* socket closed */
             goto fail;
         }

         iov.iov_base += rc;
         iov.iov_len -= rc;
         read_bytes += rc;
     } while (read_bytes != VHOST_USER_HDR_SIZE);

     /* qio_channel_readv_full will make socket fds blocking, unblock them */
     vmsg_unblock_fds(vmsg);
     if (vmsg->size > sizeof(vmsg->payload)) {
         error_report("Error: too big message request: %d, "
                      "size: vmsg->size: %u, "
                      "while sizeof(vmsg->payload) = %zu",
                      vmsg->request, vmsg->size, sizeof(vmsg->payload));
         goto fail;
     }

     struct iovec iov_payload = {
         .iov_base = (char *)&vmsg->payload,
         .iov_len = vmsg->size,
     };
     if (vmsg->size) {
         rc = qio_channel_readv_all_eof(ioc, &iov_payload, 1, &local_err);
         if (rc != 1) {
             if (local_err) {
                 error_report_err(local_err);
             }
             goto fail;
         }
     }

     return true;

 fail:
     vmsg_close_fds(vmsg);

     return false;
 }

 static coroutine_fn void vu_client_trip(void *opaque)
 {
     VuServer *server = opaque;
     VuDev *vu_dev = &server->vu_dev;

     while (!vu_dev->broken && vu_dispatch(vu_dev)) {
         /* Keep running */
     }

     vu_deinit(vu_dev);

     /* vu_deinit() should have called remove_watch() */
     assert(QTAILQ_EMPTY(&server->vu_fd_watches));

     object_unref(OBJECT(server->sioc));
     server->sioc = NULL;

     object_unref(OBJECT(server->ioc));
     server->ioc = NULL;

     server->co_trip = NULL;
     if (server->restart_listener_bh) {
         qemu_bh_schedule(server->restart_listener_bh);
     }
     aio_wait_kick();
 }

 /*
  * a wrapper for vu_kick_cb
  *
  * since aio_dispatch can only pass one user data pointer to the
  * callback function, pack VuDev and pvt into a struct. Then unpack it
  * and pass them to vu_kick_cb
  */
 static void kick_handler(void *opaque)
 {
     VuFdWatch *vu_fd_watch = opaque;
     VuDev *vu_dev = vu_fd_watch->vu_dev;

     vu_fd_watch->cb(vu_dev, 0, vu_fd_watch->pvt);

     /* Stop vu_client_trip() if an error occurred in vu_fd_watch->cb() */
     if (vu_dev->broken) {
         VuServer *server = container_of(vu_dev, VuServer, vu_dev);

         qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
     }
 }

 static VuFdWatch *find_vu_fd_watch(VuServer *server, int fd)
 {

     VuFdWatch *vu_fd_watch, *next;
     QTAILQ_FOREACH_SAFE(vu_fd_watch, &server->vu_fd_watches, next, next) {
         if (vu_fd_watch->fd == fd) {
             return vu_fd_watch;
         }
     }
     return NULL;
 }

 static void
 set_watch(VuDev *vu_dev, int fd, int vu_evt,
           vu_watch_cb cb, void *pvt)
 {

     VuServer *server = container_of(vu_dev, VuServer, vu_dev);
     g_assert(vu_dev);
     g_assert(fd >= 0);
     g_assert(cb);

     VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);

     if (!vu_fd_watch) {
         VuFdWatch *vu_fd_watch = g_new0(VuFdWatch, 1);

         QTAILQ_INSERT_TAIL(&server->vu_fd_watches, vu_fd_watch, next);

         vu_fd_watch->fd = fd;
         vu_fd_watch->cb = cb;
         qemu_set_nonblock(fd);
         aio_set_fd_handler(server->ioc->ctx, fd, true, kick_handler,
                            NULL, NULL, vu_fd_watch);
         vu_fd_watch->vu_dev = vu_dev;
         vu_fd_watch->pvt = pvt;
     }
 }


 static void remove_watch(VuDev *vu_dev, int fd)
 {
     VuServer *server;
     g_assert(vu_dev);
     g_assert(fd >= 0);

     server = container_of(vu_dev, VuServer, vu_dev);

     VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);

     if (!vu_fd_watch) {
         return;
     }
     aio_set_fd_handler(server->ioc->ctx, fd, true, NULL, NULL, NULL, NULL);

     QTAILQ_REMOVE(&server->vu_fd_watches, vu_fd_watch, next);
     g_free(vu_fd_watch);
 }


 static void vu_accept(QIONetListener *listener, QIOChannelSocket *sioc,
                       gpointer opaque)
 {
     VuServer *server = opaque;

     if (server->sioc) {
         warn_report("Only one vhost-user client is allowed to "
                     "connect the server one time");
         return;
     }

     if (!vu_init(&server->vu_dev, server->max_queues, sioc->fd, panic_cb,
                  vu_message_read, set_watch, remove_watch, server->vu_iface)) {
         error_report("Failed to initialize libvhost-user");
         return;
     }

     /*
      * Unset the callback function for network listener to make another
      * vhost-user client keeping waiting until this client disconnects
      */
     qio_net_listener_set_client_func(server->listener,
                                      NULL,
                                      NULL,
                                      NULL);
     server->sioc = sioc;
     /*
      * Increase the object reference, so sioc will not freed by
      * qio_net_listener_channel_func which will call object_unref(OBJECT(sioc))
      */
     object_ref(OBJECT(server->sioc));
     qio_channel_set_name(QIO_CHANNEL(sioc), "vhost-user client");
     server->ioc = QIO_CHANNEL(sioc);
     object_ref(OBJECT(server->ioc));

     /* TODO vu_message_write() spins if non-blocking! */
     qio_channel_set_blocking(server->ioc, false, NULL);

     server->co_trip = qemu_coroutine_create(vu_client_trip, server);

     aio_context_acquire(server->ctx);
     vhost_user_server_attach_aio_context(server, server->ctx);
     aio_context_release(server->ctx);
 }

 void vhost_user_server_stop(VuServer *server)
 {
     aio_context_acquire(server->ctx);

     qemu_bh_delete(server->restart_listener_bh);
     server->restart_listener_bh = NULL;

     if (server->sioc) {
         VuFdWatch *vu_fd_watch;

         QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
             aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
                                NULL, NULL, NULL, vu_fd_watch);
         }

         qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);

         AIO_WAIT_WHILE(server->ctx, server->co_trip);
     }

     aio_context_release(server->ctx);

     if (server->listener) {
         qio_net_listener_disconnect(server->listener);
         object_unref(OBJECT(server->listener));
     }
 }

 /*
  * Allow the next client to connect to the server. Called from a BH in the main
  * loop.
  */
 static void restart_listener_bh(void *opaque)
 {
     VuServer *server = opaque;

     qio_net_listener_set_client_func(server->listener, vu_accept, server,
                                      NULL);
 }

 /* Called with ctx acquired */
 void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx)
 {
     VuFdWatch *vu_fd_watch;

     server->ctx = ctx;

     if (!server->sioc) {
         return;
     }

     qio_channel_attach_aio_context(server->ioc, ctx);

     QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
         aio_set_fd_handler(ctx, vu_fd_watch->fd, true, kick_handler, NULL,
                            NULL, vu_fd_watch);
     }

     aio_co_schedule(ctx, server->co_trip);
 }

 /* Called with server->ctx acquired */
 void vhost_user_server_detach_aio_context(VuServer *server)
 {
     if (server->sioc) {
         VuFdWatch *vu_fd_watch;

         QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
             aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
                                NULL, NULL, NULL, vu_fd_watch);
         }

         qio_channel_detach_aio_context(server->ioc);
     }

     server->ctx = NULL;
 }

 bool vhost_user_server_start(VuServer *server,
                              SocketAddress *socket_addr,
                              AioContext *ctx,
                              uint16_t max_queues,
                              const VuDevIface *vu_iface,
                              Error **errp)
 {
     QEMUBH *bh;
     QIONetListener *listener;

     if (socket_addr->type != SOCKET_ADDRESS_TYPE_UNIX &&
         socket_addr->type != SOCKET_ADDRESS_TYPE_FD) {
         error_setg(errp, "Only socket address types 'unix' and 'fd' are supported");
         return false;
     }

     listener = qio_net_listener_new();
     if (qio_net_listener_open_sync(listener, socket_addr, 1,
                                    errp) < 0) {
         object_unref(OBJECT(listener));
         return false;
     }

     bh = qemu_bh_new(restart_listener_bh, server);

     /* zero out unspecified fields */
     *server = (VuServer) {
         .listener              = listener,
         .restart_listener_bh   = bh,
         .vu_iface              = vu_iface,
         .max_queues            = max_queues,
         .ctx                   = ctx,
     };

     qio_net_listener_set_name(server->listener, "vhost-user-backend-listener");

     qio_net_listener_set_client_func(server->listener,
                                      vu_accept,
                                      server,
                                      NULL);

     QTAILQ_INIT(&server->vu_fd_watches);
     return true;
 }
	/*
	* Sharing QEMU devices via vhost-user protocol
	*
	* Copyright (c) Coiby Xu <coiby.xu@gmail.com>.
	* Copyright (c) 2020 Red Hat, Inc.
	*
	* This work is licensed under the terms of the GNU GPL, version 2 or
	* later. See the COPYING file in the top-level directory.
	*/
	#include "qemu/osdep.h"
	#include "qemu/main-loop.h"
	#include "qemu/vhost-user-server.h"
	#include "block/aio-wait.h"

	/*
	* Theory of operation:
	*
	* VuServer is started and stopped by vhost_user_server_start() and
	* vhost_user_server_stop() from the main loop thread. Starting the server
	* opens a vhost-user UNIX domain socket and listens for incoming connections.
	* Only one connection is allowed at a time.
	*
	* The connection is handled by the vu_client_trip() coroutine in the
	* VuServer->ctx AioContext. The coroutine consists of a vu_dispatch() loop
	* where libvhost-user calls vu_message_read() to receive the next vhost-user
	* protocol messages over the UNIX domain socket.
	*
	* When virtqueues are set up libvhost-user calls set_watch() to monitor kick
	* fds. These fds are also handled in the VuServer->ctx AioContext.
	*
	* Both vu_client_trip() and kick fd monitoring can be stopped by shutting down
	* the socket connection. Shutting down the socket connection causes
	* vu_message_read() to fail since no more data can be received from the socket.
	* After vu_dispatch() fails, vu_client_trip() calls vu_deinit() to stop
	* libvhost-user before terminating the coroutine. vu_deinit() calls
	* remove_watch() to stop monitoring kick fds and this stops virtqueue
	* processing.
	*
	* When vu_client_trip() has finished cleaning up it schedules a BH in the main
	* loop thread to accept the next client connection.
	*
	* When libvhost-user detects an error it calls panic_cb() and sets the
	* dev->broken flag. Both vu_client_trip() and kick fd processing stop when
	* the dev->broken flag is set.
	*
	* It is possible to switch AioContexts using
	* vhost_user_server_detach_aio_context() and
	* vhost_user_server_attach_aio_context(). They stop monitoring fds in the old
	* AioContext and resume monitoring in the new AioContext. The vu_client_trip()
	* coroutine remains in a yielded state during the switch. This is made
	* possible by QIOChannel's support for spurious coroutine re-entry in
	* qio_channel_yield(). The coroutine will restart I/O when re-entered from the
	* new AioContext.
	*/

	static void vmsg_close_fds(VhostUserMsg *vmsg)
	{
	int i;
	for (i = 0; i < vmsg->fd_num; i++) {
	close(vmsg->fds[i]);
	}
	}

	static void vmsg_unblock_fds(VhostUserMsg *vmsg)
	{
	int i;
	for (i = 0; i < vmsg->fd_num; i++) {
	qemu_set_nonblock(vmsg->fds[i]);
	}
	}

	static void panic_cb(VuDev vu_dev, const char buf)
	{
	error_report("vu_panic: %s", buf);
	}

	static bool coroutine_fn
	vu_message_read(VuDev vu_dev, int conn_fd, VhostUserMsg vmsg)
	{
	struct iovec iov = {
	.iov_base = (char *)vmsg,
	.iov_len = VHOST_USER_HDR_SIZE,
	};
	int rc, read_bytes = 0;
	Error *local_err = NULL;
	const size_t max_fds = G_N_ELEMENTS(vmsg->fds);
	VuServer *server = container_of(vu_dev, VuServer, vu_dev);
	QIOChannel *ioc = server->ioc;

	vmsg->fd_num = 0;
	if (!ioc) {
	error_report_err(local_err);
	goto fail;
	}

	assert(qemu_in_coroutine());
	do {
	size_t nfds = 0;
	int *fds = NULL;

	/*
	* qio_channel_readv_full may have short reads, keeping calling it
	* until getting VHOST_USER_HDR_SIZE or 0 bytes in total
	*/
	rc = qio_channel_readv_full(ioc, &iov, 1, &fds, &nfds, &local_err);
	if (rc < 0) {
	if (rc == QIO_CHANNEL_ERR_BLOCK) {
	assert(local_err == NULL);
	qio_channel_yield(ioc, G_IO_IN);
	continue;
	} else {
	error_report_err(local_err);
	goto fail;
	}
	}

	if (nfds > 0) {
	if (vmsg->fd_num + nfds > max_fds) {
	error_report("A maximum of %zu fds are allowed, "
	"however got %zu fds now",
	max_fds, vmsg->fd_num + nfds);
	g_free(fds);
	goto fail;
	}
	memcpy(vmsg->fds + vmsg->fd_num, fds, nfds * sizeof(vmsg->fds[0]));
	vmsg->fd_num += nfds;
	g_free(fds);
	}

	if (rc == 0) { /* socket closed */
	goto fail;
	}

	iov.iov_base += rc;
	iov.iov_len -= rc;
	read_bytes += rc;
	} while (read_bytes != VHOST_USER_HDR_SIZE);

	/* qio_channel_readv_full will make socket fds blocking, unblock them */
	vmsg_unblock_fds(vmsg);
	if (vmsg->size > sizeof(vmsg->payload)) {
	error_report("Error: too big message request: %d, "
	"size: vmsg->size: %u, "
	"while sizeof(vmsg->payload) = %zu",
	vmsg->request, vmsg->size, sizeof(vmsg->payload));
	goto fail;
	}

	struct iovec iov_payload = {
	.iov_base = (char *)&vmsg->payload,
	.iov_len = vmsg->size,
	};
	if (vmsg->size) {
	rc = qio_channel_readv_all_eof(ioc, &iov_payload, 1, &local_err);
	if (rc != 1) {
	if (local_err) {
	error_report_err(local_err);
	}
	goto fail;
	}
	}

	return true;

	fail:
	vmsg_close_fds(vmsg);

	return false;
	}

	static coroutine_fn void vu_client_trip(void *opaque)
	{
	VuServer *server = opaque;
	VuDev *vu_dev = &server->vu_dev;

	while (!vu_dev->broken && vu_dispatch(vu_dev)) {
	/* Keep running */
	}

	vu_deinit(vu_dev);

	/* vu_deinit() should have called remove_watch() */
	assert(QTAILQ_EMPTY(&server->vu_fd_watches));

	object_unref(OBJECT(server->sioc));
	server->sioc = NULL;

	object_unref(OBJECT(server->ioc));
	server->ioc = NULL;

	server->co_trip = NULL;
	if (server->restart_listener_bh) {
	qemu_bh_schedule(server->restart_listener_bh);
	}
	aio_wait_kick();
	}

	/*
	* a wrapper for vu_kick_cb
	*
	* since aio_dispatch can only pass one user data pointer to the
	* callback function, pack VuDev and pvt into a struct. Then unpack it
	* and pass them to vu_kick_cb
	*/
	static void kick_handler(void *opaque)
	{
	VuFdWatch *vu_fd_watch = opaque;
	VuDev *vu_dev = vu_fd_watch->vu_dev;

	vu_fd_watch->cb(vu_dev, 0, vu_fd_watch->pvt);

	/* Stop vu_client_trip() if an error occurred in vu_fd_watch->cb() */
	if (vu_dev->broken) {
	VuServer *server = container_of(vu_dev, VuServer, vu_dev);

	qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
	}
	}

	static VuFdWatch find_vu_fd_watch(VuServer server, int fd)
	{

	VuFdWatch vu_fd_watch, next;
	QTAILQ_FOREACH_SAFE(vu_fd_watch, &server->vu_fd_watches, next, next) {
	if (vu_fd_watch->fd == fd) {
	return vu_fd_watch;
	}
	}
	return NULL;
	}

	static void
	set_watch(VuDev *vu_dev, int fd, int vu_evt,
	vu_watch_cb cb, void *pvt)
	{

	VuServer *server = container_of(vu_dev, VuServer, vu_dev);
	g_assert(vu_dev);
	g_assert(fd >= 0);
	g_assert(cb);

	VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);

	if (!vu_fd_watch) {
	VuFdWatch *vu_fd_watch = g_new0(VuFdWatch, 1);

	QTAILQ_INSERT_TAIL(&server->vu_fd_watches, vu_fd_watch, next);

	vu_fd_watch->fd = fd;
	vu_fd_watch->cb = cb;
	qemu_set_nonblock(fd);
	aio_set_fd_handler(server->ioc->ctx, fd, true, kick_handler,
	NULL, NULL, vu_fd_watch);
	vu_fd_watch->vu_dev = vu_dev;
	vu_fd_watch->pvt = pvt;
	}
	}


	static void remove_watch(VuDev *vu_dev, int fd)
	{
	VuServer *server;
	g_assert(vu_dev);
	g_assert(fd >= 0);

	server = container_of(vu_dev, VuServer, vu_dev);

	VuFdWatch *vu_fd_watch = find_vu_fd_watch(server, fd);

	if (!vu_fd_watch) {
	return;
	}
	aio_set_fd_handler(server->ioc->ctx, fd, true, NULL, NULL, NULL, NULL);

	QTAILQ_REMOVE(&server->vu_fd_watches, vu_fd_watch, next);
	g_free(vu_fd_watch);
	}


	static void vu_accept(QIONetListener listener, QIOChannelSocket sioc,
	gpointer opaque)
	{
	VuServer *server = opaque;

	if (server->sioc) {
	warn_report("Only one vhost-user client is allowed to "
	"connect the server one time");
	return;
	}

	if (!vu_init(&server->vu_dev, server->max_queues, sioc->fd, panic_cb,
	vu_message_read, set_watch, remove_watch, server->vu_iface)) {
	error_report("Failed to initialize libvhost-user");
	return;
	}

	/*
	* Unset the callback function for network listener to make another
	* vhost-user client keeping waiting until this client disconnects
	*/
	qio_net_listener_set_client_func(server->listener,
	NULL,
	NULL,
	NULL);
	server->sioc = sioc;
	/*
	* Increase the object reference, so sioc will not freed by
	* qio_net_listener_channel_func which will call object_unref(OBJECT(sioc))
	*/
	object_ref(OBJECT(server->sioc));
	qio_channel_set_name(QIO_CHANNEL(sioc), "vhost-user client");
	server->ioc = QIO_CHANNEL(sioc);
	object_ref(OBJECT(server->ioc));

	/* TODO vu_message_write() spins if non-blocking! */
	qio_channel_set_blocking(server->ioc, false, NULL);

	server->co_trip = qemu_coroutine_create(vu_client_trip, server);

	aio_context_acquire(server->ctx);
	vhost_user_server_attach_aio_context(server, server->ctx);
	aio_context_release(server->ctx);
	}

	void vhost_user_server_stop(VuServer *server)
	{
	aio_context_acquire(server->ctx);

	qemu_bh_delete(server->restart_listener_bh);
	server->restart_listener_bh = NULL;

	if (server->sioc) {
	VuFdWatch *vu_fd_watch;

	QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
	aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
	NULL, NULL, NULL, vu_fd_watch);
	}

	qio_channel_shutdown(server->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);

	AIO_WAIT_WHILE(server->ctx, server->co_trip);
	}

	aio_context_release(server->ctx);

	if (server->listener) {
	qio_net_listener_disconnect(server->listener);
	object_unref(OBJECT(server->listener));
	}
	}

	/*
	* Allow the next client to connect to the server. Called from a BH in the main
	* loop.
	*/
	static void restart_listener_bh(void *opaque)
	{
	VuServer *server = opaque;

	qio_net_listener_set_client_func(server->listener, vu_accept, server,
	NULL);
	}

	/* Called with ctx acquired */
	void vhost_user_server_attach_aio_context(VuServer server, AioContext ctx)
	{
	VuFdWatch *vu_fd_watch;

	server->ctx = ctx;

	if (!server->sioc) {
	return;
	}

	qio_channel_attach_aio_context(server->ioc, ctx);

	QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
	aio_set_fd_handler(ctx, vu_fd_watch->fd, true, kick_handler, NULL,
	NULL, vu_fd_watch);
	}

	aio_co_schedule(ctx, server->co_trip);
	}

	/* Called with server->ctx acquired */
	void vhost_user_server_detach_aio_context(VuServer *server)
	{
	if (server->sioc) {
	VuFdWatch *vu_fd_watch;

	QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
	aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
	NULL, NULL, NULL, vu_fd_watch);
	}

	qio_channel_detach_aio_context(server->ioc);
	}

	server->ctx = NULL;
	}

	bool vhost_user_server_start(VuServer *server,
	SocketAddress *socket_addr,
	AioContext *ctx,
	uint16_t max_queues,
	const VuDevIface *vu_iface,
	Error **errp)
	{
	QEMUBH *bh;
	QIONetListener *listener;

	if (socket_addr->type != SOCKET_ADDRESS_TYPE_UNIX &&
	socket_addr->type != SOCKET_ADDRESS_TYPE_FD) {
	error_setg(errp, "Only socket address types 'unix' and 'fd' are supported");
	return false;
	}

	listener = qio_net_listener_new();
	if (qio_net_listener_open_sync(listener, socket_addr, 1,
	errp) < 0) {
	object_unref(OBJECT(listener));
	return false;
	}

	bh = qemu_bh_new(restart_listener_bh, server);

	/* zero out unspecified fields */
	*server = (VuServer) {
	.listener = listener,
	.restart_listener_bh = bh,
	.vu_iface = vu_iface,
	.max_queues = max_queues,
	.ctx = ctx,
	};

	qio_net_listener_set_name(server->listener, "vhost-user-backend-listener");

	qio_net_listener_set_client_func(server->listener,
	vu_accept,
	server,
	NULL);

	QTAILQ_INIT(&server->vu_fd_watches);
	return true;
	}