block/export/vhost-user-blk-server.c - qemu - Git at Google

 /*
  * Sharing QEMU block devices via vhost-user protocol
  *
  * Parts of the code based on nbd/server.c.
  *
  * 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/error-report.h"
 #include "block/block.h"
 #include "subprojects/libvhost-user/libvhost-user.h" /* only for the type definitions */
 #include "standard-headers/linux/virtio_blk.h"
 #include "qemu/vhost-user-server.h"
 #include "vhost-user-blk-server.h"
 #include "qapi/error.h"
 #include "qom/object_interfaces.h"
 #include "util/block-helpers.h"
 #include "virtio-blk-handler.h"

 enum {
     VHOST_USER_BLK_NUM_QUEUES_DEFAULT = 1,
 };

 typedef struct VuBlkReq {
     VuVirtqElement elem;
     VuServer *server;
     struct VuVirtq *vq;
 } VuBlkReq;

 /* vhost user block device */
 typedef struct {
     BlockExport export;
     VuServer vu_server;
     VirtioBlkHandler handler;
     QIOChannelSocket *sioc;
     struct virtio_blk_config blkcfg;
 } VuBlkExport;

 static void vu_blk_req_complete(VuBlkReq *req, size_t in_len)
 {
     VuDev *vu_dev = &req->server->vu_dev;

     vu_queue_push(vu_dev, req->vq, &req->elem, in_len);
     vu_queue_notify(vu_dev, req->vq);

     free(req);
 }

 /*
  * Called with server in_flight counter increased, must decrease before
  * returning.
  */
 static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
 {
     VuBlkReq *req = opaque;
     VuServer *server = req->server;
     VuVirtqElement *elem = &req->elem;
     VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
     VirtioBlkHandler *handler = &vexp->handler;
     struct iovec *in_iov = elem->in_sg;
     struct iovec *out_iov = elem->out_sg;
     unsigned in_num = elem->in_num;
     unsigned out_num = elem->out_num;
     int in_len;

     in_len = virtio_blk_process_req(handler, in_iov, out_iov,
                                     in_num, out_num);
     if (in_len < 0) {
         free(req);
         vhost_user_server_dec_in_flight(server);
         return;
     }

     vu_blk_req_complete(req, in_len);
     vhost_user_server_dec_in_flight(server);
 }

 static void vu_blk_process_vq(VuDev *vu_dev, int idx)
 {
     VuServer *server = container_of(vu_dev, VuServer, vu_dev);
     VuVirtq *vq = vu_get_queue(vu_dev, idx);

     while (1) {
         VuBlkReq *req;

         req = vu_queue_pop(vu_dev, vq, sizeof(VuBlkReq));
         if (!req) {
             break;
         }

         req->server = server;
         req->vq = vq;

         Coroutine *co =
             qemu_coroutine_create(vu_blk_virtio_process_req, req);

         vhost_user_server_inc_in_flight(server);
         qemu_coroutine_enter(co);
     }
 }

 static void vu_blk_queue_set_started(VuDev *vu_dev, int idx, bool started)
 {
     VuVirtq *vq;

     assert(vu_dev);

     vq = vu_get_queue(vu_dev, idx);
     vu_set_queue_handler(vu_dev, vq, started ? vu_blk_process_vq : NULL);
 }

 static uint64_t vu_blk_get_features(VuDev *dev)
 {
     uint64_t features;
     VuServer *server = container_of(dev, VuServer, vu_dev);
     VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
     features = 1ull << VIRTIO_BLK_F_SIZE_MAX |
                1ull << VIRTIO_BLK_F_SEG_MAX |
                1ull << VIRTIO_BLK_F_TOPOLOGY |
                1ull << VIRTIO_BLK_F_BLK_SIZE |
                1ull << VIRTIO_BLK_F_FLUSH |
                1ull << VIRTIO_BLK_F_DISCARD |
                1ull << VIRTIO_BLK_F_WRITE_ZEROES |
                1ull << VIRTIO_BLK_F_CONFIG_WCE |
                1ull << VIRTIO_BLK_F_MQ |
                1ull << VIRTIO_F_VERSION_1 |
                1ull << VIRTIO_RING_F_INDIRECT_DESC |
                1ull << VIRTIO_RING_F_EVENT_IDX |
                1ull << VHOST_USER_F_PROTOCOL_FEATURES;

     if (!vexp->handler.writable) {
         features |= 1ull << VIRTIO_BLK_F_RO;
     }

     return features;
 }

 static uint64_t vu_blk_get_protocol_features(VuDev *dev)
 {
     return 1ull << VHOST_USER_PROTOCOL_F_CONFIG;
 }

 static int
 vu_blk_get_config(VuDev *vu_dev, uint8_t *config, uint32_t len)
 {
     VuServer *server = container_of(vu_dev, VuServer, vu_dev);
     VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);

     if (len > sizeof(struct virtio_blk_config)) {
         return -1;
     }

     memcpy(config, &vexp->blkcfg, len);
     return 0;
 }

 static int
 vu_blk_set_config(VuDev *vu_dev, const uint8_t *data,
                     uint32_t offset, uint32_t size, uint32_t flags)
 {
     VuServer *server = container_of(vu_dev, VuServer, vu_dev);
     VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
     uint8_t wce;

     /* don't support live migration */
     if (flags != VHOST_SET_CONFIG_TYPE_FRONTEND) {
         return -EINVAL;
     }

     if (offset != offsetof(struct virtio_blk_config, wce) ||
         size != 1) {
         return -EINVAL;
     }

     wce = *data;
     vexp->blkcfg.wce = wce;
     blk_set_enable_write_cache(vexp->export.blk, wce);
     return 0;
 }

 /*
  * When the client disconnects, it sends a VHOST_USER_NONE request
  * and vu_process_message will simple call exit which cause the VM
  * to exit abruptly.
  * To avoid this issue,  process VHOST_USER_NONE request ahead
  * of vu_process_message.
  *
  */
 static int vu_blk_process_msg(VuDev *dev, VhostUserMsg *vmsg, int *do_reply)
 {
     if (vmsg->request == VHOST_USER_NONE) {
         dev->panic(dev, "disconnect");
         return true;
     }
     return false;
 }

 static const VuDevIface vu_blk_iface = {
     .get_features          = vu_blk_get_features,
     .queue_set_started     = vu_blk_queue_set_started,
     .get_protocol_features = vu_blk_get_protocol_features,
     .get_config            = vu_blk_get_config,
     .set_config            = vu_blk_set_config,
     .process_msg           = vu_blk_process_msg,
 };

 static void blk_aio_attached(AioContext *ctx, void *opaque)
 {
     VuBlkExport *vexp = opaque;

     /*
      * The actual attach will happen in vu_blk_drained_end() and we just
      * restore ctx here.
      */
     vexp->export.ctx = ctx;
 }

 static void blk_aio_detach(void *opaque)
 {
     VuBlkExport *vexp = opaque;

     /*
      * The actual detach already happened in vu_blk_drained_begin() but from
      * this point on we must not access ctx anymore.
      */
     vexp->export.ctx = NULL;
 }

 static void
 vu_blk_initialize_config(BlockDriverState *bs,
                          struct virtio_blk_config *config,
                          uint32_t blk_size,
                          uint16_t num_queues)
 {
     config->capacity =
         cpu_to_le64(bdrv_getlength(bs) >> VIRTIO_BLK_SECTOR_BITS);
     config->blk_size = cpu_to_le32(blk_size);
     config->size_max = cpu_to_le32(0);
     config->seg_max = cpu_to_le32(128 - 2);
     config->min_io_size = cpu_to_le16(1);
     config->opt_io_size = cpu_to_le32(1);
     config->num_queues = cpu_to_le16(num_queues);
     config->max_discard_sectors =
         cpu_to_le32(VIRTIO_BLK_MAX_DISCARD_SECTORS);
     config->max_discard_seg = cpu_to_le32(1);
     config->discard_sector_alignment =
         cpu_to_le32(blk_size >> VIRTIO_BLK_SECTOR_BITS);
     config->max_write_zeroes_sectors
         = cpu_to_le32(VIRTIO_BLK_MAX_WRITE_ZEROES_SECTORS);
     config->max_write_zeroes_seg = cpu_to_le32(1);
 }

 static void vu_blk_exp_request_shutdown(BlockExport *exp)
 {
     VuBlkExport *vexp = container_of(exp, VuBlkExport, export);

     vhost_user_server_stop(&vexp->vu_server);
 }

 static void vu_blk_exp_resize(void *opaque)
 {
     VuBlkExport *vexp = opaque;
     BlockDriverState *bs = blk_bs(vexp->handler.blk);
     int64_t new_size = bdrv_getlength(bs);

     if (new_size < 0) {
         error_printf("Failed to get length of block node '%s'",
                      bdrv_get_node_name(bs));
         return;
     }

     vexp->blkcfg.capacity = cpu_to_le64(new_size >> VIRTIO_BLK_SECTOR_BITS);

     vu_config_change_msg(&vexp->vu_server.vu_dev);
 }

 static void vu_blk_drained_begin(void *opaque)
 {
     VuBlkExport *vexp = opaque;

     vexp->vu_server.quiescing = true;
     vhost_user_server_detach_aio_context(&vexp->vu_server);
 }

 static void vu_blk_drained_end(void *opaque)
 {
     VuBlkExport *vexp = opaque;

     vexp->vu_server.quiescing = false;
     vhost_user_server_attach_aio_context(&vexp->vu_server, vexp->export.ctx);
 }

 /*
  * Ensures that bdrv_drained_begin() waits until in-flight requests complete
  * and the server->co_trip coroutine has terminated. It will be restarted in
  * vhost_user_server_attach_aio_context().
  */
 static bool vu_blk_drained_poll(void *opaque)
 {
     VuBlkExport *vexp = opaque;
     VuServer *server = &vexp->vu_server;

     return server->co_trip || vhost_user_server_has_in_flight(server);
 }

 static const BlockDevOps vu_blk_dev_ops = {
     .drained_begin = vu_blk_drained_begin,
     .drained_end   = vu_blk_drained_end,
     .drained_poll  = vu_blk_drained_poll,
     .resize_cb = vu_blk_exp_resize,
 };

 static int vu_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
                              Error **errp)
 {
     VuBlkExport *vexp = container_of(exp, VuBlkExport, export);
     BlockExportOptionsVhostUserBlk *vu_opts = &opts->u.vhost_user_blk;
     Error *local_err = NULL;
     uint64_t logical_block_size;
     uint16_t num_queues = VHOST_USER_BLK_NUM_QUEUES_DEFAULT;

     vexp->blkcfg.wce = 0;

     if (vu_opts->has_logical_block_size) {
         logical_block_size = vu_opts->logical_block_size;
     } else {
         logical_block_size = VIRTIO_BLK_SECTOR_SIZE;
     }
     check_block_size(exp->id, "logical-block-size", logical_block_size,
                      &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }

     if (vu_opts->has_num_queues) {
         num_queues = vu_opts->num_queues;
     }
     if (num_queues == 0) {
         error_setg(errp, "num-queues must be greater than 0");
         return -EINVAL;
     }
     vexp->handler.blk = exp->blk;
     vexp->handler.serial = g_strdup("vhost_user_blk");
     vexp->handler.logical_block_size = logical_block_size;
     vexp->handler.writable = opts->writable;

     vu_blk_initialize_config(blk_bs(exp->blk), &vexp->blkcfg,
                              logical_block_size, num_queues);

     blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
                                  vexp);

     blk_set_dev_ops(exp->blk, &vu_blk_dev_ops, vexp);

     if (!vhost_user_server_start(&vexp->vu_server, vu_opts->addr, exp->ctx,
                                  num_queues, &vu_blk_iface, errp)) {
         blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
                                         blk_aio_detach, vexp);
         g_free(vexp->handler.serial);
         return -EADDRNOTAVAIL;
     }

     return 0;
 }

 static void vu_blk_exp_delete(BlockExport *exp)
 {
     VuBlkExport *vexp = container_of(exp, VuBlkExport, export);

     blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
                                     vexp);
     g_free(vexp->handler.serial);
 }

 const BlockExportDriver blk_exp_vhost_user_blk = {
     .type               = BLOCK_EXPORT_TYPE_VHOST_USER_BLK,
     .instance_size      = sizeof(VuBlkExport),
     .create             = vu_blk_exp_create,
     .delete             = vu_blk_exp_delete,
     .request_shutdown   = vu_blk_exp_request_shutdown,
 };
	/*
	* Sharing QEMU block devices via vhost-user protocol
	*
	* Parts of the code based on nbd/server.c.
	*
	* 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/error-report.h"
	#include "block/block.h"
	#include "subprojects/libvhost-user/libvhost-user.h" /* only for the type definitions */
	#include "standard-headers/linux/virtio_blk.h"
	#include "qemu/vhost-user-server.h"
	#include "vhost-user-blk-server.h"
	#include "qapi/error.h"
	#include "qom/object_interfaces.h"
	#include "util/block-helpers.h"
	#include "virtio-blk-handler.h"

	enum {
	VHOST_USER_BLK_NUM_QUEUES_DEFAULT = 1,
	};

	typedef struct VuBlkReq {
	VuVirtqElement elem;
	VuServer *server;
	struct VuVirtq *vq;
	} VuBlkReq;

	/* vhost user block device */
	typedef struct {
	BlockExport export;
	VuServer vu_server;
	VirtioBlkHandler handler;
	QIOChannelSocket *sioc;
	struct virtio_blk_config blkcfg;
	} VuBlkExport;

	static void vu_blk_req_complete(VuBlkReq *req, size_t in_len)
	{
	VuDev *vu_dev = &req->server->vu_dev;

	vu_queue_push(vu_dev, req->vq, &req->elem, in_len);
	vu_queue_notify(vu_dev, req->vq);

	free(req);
	}

	/*
	* Called with server in_flight counter increased, must decrease before
	* returning.
	*/
	static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
	{
	VuBlkReq *req = opaque;
	VuServer *server = req->server;
	VuVirtqElement *elem = &req->elem;
	VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
	VirtioBlkHandler *handler = &vexp->handler;
	struct iovec *in_iov = elem->in_sg;
	struct iovec *out_iov = elem->out_sg;
	unsigned in_num = elem->in_num;
	unsigned out_num = elem->out_num;
	int in_len;

	in_len = virtio_blk_process_req(handler, in_iov, out_iov,
	in_num, out_num);
	if (in_len < 0) {
	free(req);
	vhost_user_server_dec_in_flight(server);
	return;
	}

	vu_blk_req_complete(req, in_len);
	vhost_user_server_dec_in_flight(server);
	}

	static void vu_blk_process_vq(VuDev *vu_dev, int idx)
	{
	VuServer *server = container_of(vu_dev, VuServer, vu_dev);
	VuVirtq *vq = vu_get_queue(vu_dev, idx);

	while (1) {
	VuBlkReq *req;

	req = vu_queue_pop(vu_dev, vq, sizeof(VuBlkReq));
	if (!req) {
	break;
	}

	req->server = server;
	req->vq = vq;

	Coroutine *co =
	qemu_coroutine_create(vu_blk_virtio_process_req, req);

	vhost_user_server_inc_in_flight(server);
	qemu_coroutine_enter(co);
	}
	}

	static void vu_blk_queue_set_started(VuDev *vu_dev, int idx, bool started)
	{
	VuVirtq *vq;

	assert(vu_dev);

	vq = vu_get_queue(vu_dev, idx);
	vu_set_queue_handler(vu_dev, vq, started ? vu_blk_process_vq : NULL);
	}

	static uint64_t vu_blk_get_features(VuDev *dev)
	{
	uint64_t features;
	VuServer *server = container_of(dev, VuServer, vu_dev);
	VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
	features = 1ull << VIRTIO_BLK_F_SIZE_MAX \|
	1ull << VIRTIO_BLK_F_SEG_MAX \|
	1ull << VIRTIO_BLK_F_TOPOLOGY \|
	1ull << VIRTIO_BLK_F_BLK_SIZE \|
	1ull << VIRTIO_BLK_F_FLUSH \|
	1ull << VIRTIO_BLK_F_DISCARD \|
	1ull << VIRTIO_BLK_F_WRITE_ZEROES \|
	1ull << VIRTIO_BLK_F_CONFIG_WCE \|
	1ull << VIRTIO_BLK_F_MQ \|
	1ull << VIRTIO_F_VERSION_1 \|
	1ull << VIRTIO_RING_F_INDIRECT_DESC \|
	1ull << VIRTIO_RING_F_EVENT_IDX \|
	1ull << VHOST_USER_F_PROTOCOL_FEATURES;

	if (!vexp->handler.writable) {
	features \|= 1ull << VIRTIO_BLK_F_RO;
	}

	return features;
	}

	static uint64_t vu_blk_get_protocol_features(VuDev *dev)
	{
	return 1ull << VHOST_USER_PROTOCOL_F_CONFIG;
	}

	static int
	vu_blk_get_config(VuDev vu_dev, uint8_t config, uint32_t len)
	{
	VuServer *server = container_of(vu_dev, VuServer, vu_dev);
	VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);

	if (len > sizeof(struct virtio_blk_config)) {
	return -1;
	}

	memcpy(config, &vexp->blkcfg, len);
	return 0;
	}

	static int
	vu_blk_set_config(VuDev vu_dev, const uint8_t data,
	uint32_t offset, uint32_t size, uint32_t flags)
	{
	VuServer *server = container_of(vu_dev, VuServer, vu_dev);
	VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
	uint8_t wce;

	/* don't support live migration */
	if (flags != VHOST_SET_CONFIG_TYPE_FRONTEND) {
	return -EINVAL;
	}

	if (offset != offsetof(struct virtio_blk_config, wce) \|\|
	size != 1) {
	return -EINVAL;
	}

	wce = *data;
	vexp->blkcfg.wce = wce;
	blk_set_enable_write_cache(vexp->export.blk, wce);
	return 0;
	}

	/*
	* When the client disconnects, it sends a VHOST_USER_NONE request
	* and vu_process_message will simple call exit which cause the VM
	* to exit abruptly.
	* To avoid this issue, process VHOST_USER_NONE request ahead
	* of vu_process_message.
	*
	*/
	static int vu_blk_process_msg(VuDev dev, VhostUserMsg vmsg, int *do_reply)
	{
	if (vmsg->request == VHOST_USER_NONE) {
	dev->panic(dev, "disconnect");
	return true;
	}
	return false;
	}

	static const VuDevIface vu_blk_iface = {
	.get_features = vu_blk_get_features,
	.queue_set_started = vu_blk_queue_set_started,
	.get_protocol_features = vu_blk_get_protocol_features,
	.get_config = vu_blk_get_config,
	.set_config = vu_blk_set_config,
	.process_msg = vu_blk_process_msg,
	};

	static void blk_aio_attached(AioContext ctx, void opaque)
	{
	VuBlkExport *vexp = opaque;

	/*
	* The actual attach will happen in vu_blk_drained_end() and we just
	* restore ctx here.
	*/
	vexp->export.ctx = ctx;
	}

	static void blk_aio_detach(void *opaque)
	{
	VuBlkExport *vexp = opaque;

	/*
	* The actual detach already happened in vu_blk_drained_begin() but from
	* this point on we must not access ctx anymore.
	*/
	vexp->export.ctx = NULL;
	}

	static void
	vu_blk_initialize_config(BlockDriverState *bs,
	struct virtio_blk_config *config,
	uint32_t blk_size,
	uint16_t num_queues)
	{
	config->capacity =
	cpu_to_le64(bdrv_getlength(bs) >> VIRTIO_BLK_SECTOR_BITS);
	config->blk_size = cpu_to_le32(blk_size);
	config->size_max = cpu_to_le32(0);
	config->seg_max = cpu_to_le32(128 - 2);
	config->min_io_size = cpu_to_le16(1);
	config->opt_io_size = cpu_to_le32(1);
	config->num_queues = cpu_to_le16(num_queues);
	config->max_discard_sectors =
	cpu_to_le32(VIRTIO_BLK_MAX_DISCARD_SECTORS);
	config->max_discard_seg = cpu_to_le32(1);
	config->discard_sector_alignment =
	cpu_to_le32(blk_size >> VIRTIO_BLK_SECTOR_BITS);
	config->max_write_zeroes_sectors
	= cpu_to_le32(VIRTIO_BLK_MAX_WRITE_ZEROES_SECTORS);
	config->max_write_zeroes_seg = cpu_to_le32(1);
	}

	static void vu_blk_exp_request_shutdown(BlockExport *exp)
	{
	VuBlkExport *vexp = container_of(exp, VuBlkExport, export);

	vhost_user_server_stop(&vexp->vu_server);
	}

	static void vu_blk_exp_resize(void *opaque)
	{
	VuBlkExport *vexp = opaque;
	BlockDriverState *bs = blk_bs(vexp->handler.blk);
	int64_t new_size = bdrv_getlength(bs);

	if (new_size < 0) {
	error_printf("Failed to get length of block node '%s'",
	bdrv_get_node_name(bs));
	return;
	}

	vexp->blkcfg.capacity = cpu_to_le64(new_size >> VIRTIO_BLK_SECTOR_BITS);

	vu_config_change_msg(&vexp->vu_server.vu_dev);
	}

	static void vu_blk_drained_begin(void *opaque)
	{
	VuBlkExport *vexp = opaque;

	vexp->vu_server.quiescing = true;
	vhost_user_server_detach_aio_context(&vexp->vu_server);
	}

	static void vu_blk_drained_end(void *opaque)
	{
	VuBlkExport *vexp = opaque;

	vexp->vu_server.quiescing = false;
	vhost_user_server_attach_aio_context(&vexp->vu_server, vexp->export.ctx);
	}

	/*
	* Ensures that bdrv_drained_begin() waits until in-flight requests complete
	* and the server->co_trip coroutine has terminated. It will be restarted in
	* vhost_user_server_attach_aio_context().
	*/
	static bool vu_blk_drained_poll(void *opaque)
	{
	VuBlkExport *vexp = opaque;
	VuServer *server = &vexp->vu_server;

	return server->co_trip \|\| vhost_user_server_has_in_flight(server);
	}

	static const BlockDevOps vu_blk_dev_ops = {
	.drained_begin = vu_blk_drained_begin,
	.drained_end = vu_blk_drained_end,
	.drained_poll = vu_blk_drained_poll,
	.resize_cb = vu_blk_exp_resize,
	};

	static int vu_blk_exp_create(BlockExport exp, BlockExportOptions opts,
	Error **errp)
	{
	VuBlkExport *vexp = container_of(exp, VuBlkExport, export);
	BlockExportOptionsVhostUserBlk *vu_opts = &opts->u.vhost_user_blk;
	Error *local_err = NULL;
	uint64_t logical_block_size;
	uint16_t num_queues = VHOST_USER_BLK_NUM_QUEUES_DEFAULT;

	vexp->blkcfg.wce = 0;

	if (vu_opts->has_logical_block_size) {
	logical_block_size = vu_opts->logical_block_size;
	} else {
	logical_block_size = VIRTIO_BLK_SECTOR_SIZE;
	}
	check_block_size(exp->id, "logical-block-size", logical_block_size,
	&local_err);
	if (local_err) {
	error_propagate(errp, local_err);
	return -EINVAL;
	}

	if (vu_opts->has_num_queues) {
	num_queues = vu_opts->num_queues;
	}
	if (num_queues == 0) {
	error_setg(errp, "num-queues must be greater than 0");
	return -EINVAL;
	}
	vexp->handler.blk = exp->blk;
	vexp->handler.serial = g_strdup("vhost_user_blk");
	vexp->handler.logical_block_size = logical_block_size;
	vexp->handler.writable = opts->writable;

	vu_blk_initialize_config(blk_bs(exp->blk), &vexp->blkcfg,
	logical_block_size, num_queues);

	blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
	vexp);

	blk_set_dev_ops(exp->blk, &vu_blk_dev_ops, vexp);

	if (!vhost_user_server_start(&vexp->vu_server, vu_opts->addr, exp->ctx,
	num_queues, &vu_blk_iface, errp)) {
	blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
	blk_aio_detach, vexp);
	g_free(vexp->handler.serial);
	return -EADDRNOTAVAIL;
	}

	return 0;
	}

	static void vu_blk_exp_delete(BlockExport *exp)
	{
	VuBlkExport *vexp = container_of(exp, VuBlkExport, export);

	blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
	vexp);
	g_free(vexp->handler.serial);
	}

	const BlockExportDriver blk_exp_vhost_user_blk = {
	.type = BLOCK_EXPORT_TYPE_VHOST_USER_BLK,
	.instance_size = sizeof(VuBlkExport),
	.create = vu_blk_exp_create,
	.delete = vu_blk_exp_delete,
	.request_shutdown = vu_blk_exp_request_shutdown,
	};