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

 /*
  * Sharing QEMU block devices via vhost-user protocal
  *
  * 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 "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 "sysemu/block-backend.h"
 #include "util/block-helpers.h"

 enum {
     VHOST_USER_BLK_NUM_QUEUES_DEFAULT = 1,
 };
 struct virtio_blk_inhdr {
     unsigned char status;
 };

 typedef struct VuBlkReq {
     VuVirtqElement elem;
     int64_t sector_num;
     size_t size;
     struct virtio_blk_inhdr *in;
     struct virtio_blk_outhdr out;
     VuServer *server;
     struct VuVirtq *vq;
 } VuBlkReq;

 /* vhost user block device */
 typedef struct {
     BlockExport export;
     VuServer vu_server;
     uint32_t blk_size;
     QIOChannelSocket *sioc;
     struct virtio_blk_config blkcfg;
     bool writable;
 } VuBlkExport;

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

     /* IO size with 1 extra status byte */
     vu_queue_push(vu_dev, req->vq, &req->elem, req->size + 1);
     vu_queue_notify(vu_dev, req->vq);

     free(req);
 }

 static int coroutine_fn
 vu_blk_discard_write_zeroes(BlockBackend *blk, struct iovec *iov,
                             uint32_t iovcnt, uint32_t type)
 {
     struct virtio_blk_discard_write_zeroes desc;
     ssize_t size = iov_to_buf(iov, iovcnt, 0, &desc, sizeof(desc));
     if (unlikely(size != sizeof(desc))) {
         error_report("Invalid size %zd, expect %zu", size, sizeof(desc));
         return -EINVAL;
     }

     uint64_t range[2] = { le64_to_cpu(desc.sector) << 9,
                           le32_to_cpu(desc.num_sectors) << 9 };
     if (type == VIRTIO_BLK_T_DISCARD) {
         if (blk_co_pdiscard(blk, range[0], range[1]) == 0) {
             return 0;
         }
     } else if (type == VIRTIO_BLK_T_WRITE_ZEROES) {
         if (blk_co_pwrite_zeroes(blk, range[0], range[1], 0) == 0) {
             return 0;
         }
     }

     return -EINVAL;
 }

 static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
 {
     VuBlkReq *req = opaque;
     VuServer *server = req->server;
     VuVirtqElement *elem = &req->elem;
     uint32_t type;

     VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
     BlockBackend *blk = vexp->export.blk;

     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;

     /* refer to hw/block/virtio_blk.c */
     if (elem->out_num < 1 || elem->in_num < 1) {
         error_report("virtio-blk request missing headers");
         goto err;
     }

     if (unlikely(iov_to_buf(out_iov, out_num, 0, &req->out,
                             sizeof(req->out)) != sizeof(req->out))) {
         error_report("virtio-blk request outhdr too short");
         goto err;
     }

     iov_discard_front(&out_iov, &out_num, sizeof(req->out));

     if (in_iov[in_num - 1].iov_len < sizeof(struct virtio_blk_inhdr)) {
         error_report("virtio-blk request inhdr too short");
         goto err;
     }

     /* We always touch the last byte, so just see how big in_iov is.  */
     req->in = (void *)in_iov[in_num - 1].iov_base
               + in_iov[in_num - 1].iov_len
               - sizeof(struct virtio_blk_inhdr);
     iov_discard_back(in_iov, &in_num, sizeof(struct virtio_blk_inhdr));

     type = le32_to_cpu(req->out.type);
     switch (type & ~VIRTIO_BLK_T_BARRIER) {
     case VIRTIO_BLK_T_IN:
     case VIRTIO_BLK_T_OUT: {
         ssize_t ret = 0;
         bool is_write = type & VIRTIO_BLK_T_OUT;
         req->sector_num = le64_to_cpu(req->out.sector);

         if (is_write && !vexp->writable) {
             req->in->status = VIRTIO_BLK_S_IOERR;
             break;
         }

         int64_t offset = req->sector_num * vexp->blk_size;
         QEMUIOVector qiov;
         if (is_write) {
             qemu_iovec_init_external(&qiov, out_iov, out_num);
             ret = blk_co_pwritev(blk, offset, qiov.size, &qiov, 0);
         } else {
             qemu_iovec_init_external(&qiov, in_iov, in_num);
             ret = blk_co_preadv(blk, offset, qiov.size, &qiov, 0);
         }
         if (ret >= 0) {
             req->in->status = VIRTIO_BLK_S_OK;
         } else {
             req->in->status = VIRTIO_BLK_S_IOERR;
         }
         break;
     }
     case VIRTIO_BLK_T_FLUSH:
         if (blk_co_flush(blk) == 0) {
             req->in->status = VIRTIO_BLK_S_OK;
         } else {
             req->in->status = VIRTIO_BLK_S_IOERR;
         }
         break;
     case VIRTIO_BLK_T_GET_ID: {
         size_t size = MIN(iov_size(&elem->in_sg[0], in_num),
                           VIRTIO_BLK_ID_BYTES);
         snprintf(elem->in_sg[0].iov_base, size, "%s", "vhost_user_blk");
         req->in->status = VIRTIO_BLK_S_OK;
         req->size = elem->in_sg[0].iov_len;
         break;
     }
     case VIRTIO_BLK_T_DISCARD:
     case VIRTIO_BLK_T_WRITE_ZEROES: {
         int rc;

         if (!vexp->writable) {
             req->in->status = VIRTIO_BLK_S_IOERR;
             break;
         }

         rc = vu_blk_discard_write_zeroes(blk, &elem->out_sg[1], out_num, type);
         if (rc == 0) {
             req->in->status = VIRTIO_BLK_S_OK;
         } else {
             req->in->status = VIRTIO_BLK_S_IOERR;
         }
         break;
     }
     default:
         req->in->status = VIRTIO_BLK_S_UNSUPP;
         break;
     }

     vu_blk_req_complete(req);
     return;

 err:
     free(req);
 }

 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);
         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->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 |
            1ull << VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD;
 }

 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_MASTER) {
         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;

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

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

     vhost_user_server_detach_aio_context(&vexp->vu_server);
     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) >> BDRV_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(32768);
     config->max_discard_seg = cpu_to_le32(1);
     config->discard_sector_alignment = cpu_to_le32(config->blk_size >> 9);
     config->max_write_zeroes_sectors = cpu_to_le32(32768);
     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 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->writable = opts->writable;
     vexp->blkcfg.wce = 0;

     if (vu_opts->has_logical_block_size) {
         logical_block_size = vu_opts->logical_block_size;
     } else {
         logical_block_size = BDRV_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;
     }
     vexp->blk_size = logical_block_size;
     blk_set_guest_block_size(exp->blk, logical_block_size);

     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;
     }

     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);

     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);
         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);
 }

 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 protocal
	*
	* 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 "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 "sysemu/block-backend.h"
	#include "util/block-helpers.h"

	enum {
	VHOST_USER_BLK_NUM_QUEUES_DEFAULT = 1,
	};
	struct virtio_blk_inhdr {
	unsigned char status;
	};

	typedef struct VuBlkReq {
	VuVirtqElement elem;
	int64_t sector_num;
	size_t size;
	struct virtio_blk_inhdr *in;
	struct virtio_blk_outhdr out;
	VuServer *server;
	struct VuVirtq *vq;
	} VuBlkReq;

	/* vhost user block device */
	typedef struct {
	BlockExport export;
	VuServer vu_server;
	uint32_t blk_size;
	QIOChannelSocket *sioc;
	struct virtio_blk_config blkcfg;
	bool writable;
	} VuBlkExport;

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

	/* IO size with 1 extra status byte */
	vu_queue_push(vu_dev, req->vq, &req->elem, req->size + 1);
	vu_queue_notify(vu_dev, req->vq);

	free(req);
	}

	static int coroutine_fn
	vu_blk_discard_write_zeroes(BlockBackend blk, struct iovec iov,
	uint32_t iovcnt, uint32_t type)
	{
	struct virtio_blk_discard_write_zeroes desc;
	ssize_t size = iov_to_buf(iov, iovcnt, 0, &desc, sizeof(desc));
	if (unlikely(size != sizeof(desc))) {
	error_report("Invalid size %zd, expect %zu", size, sizeof(desc));
	return -EINVAL;
	}

	uint64_t range[2] = { le64_to_cpu(desc.sector) << 9,
	le32_to_cpu(desc.num_sectors) << 9 };
	if (type == VIRTIO_BLK_T_DISCARD) {
	if (blk_co_pdiscard(blk, range[0], range[1]) == 0) {
	return 0;
	}
	} else if (type == VIRTIO_BLK_T_WRITE_ZEROES) {
	if (blk_co_pwrite_zeroes(blk, range[0], range[1], 0) == 0) {
	return 0;
	}
	}

	return -EINVAL;
	}

	static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
	{
	VuBlkReq *req = opaque;
	VuServer *server = req->server;
	VuVirtqElement *elem = &req->elem;
	uint32_t type;

	VuBlkExport *vexp = container_of(server, VuBlkExport, vu_server);
	BlockBackend *blk = vexp->export.blk;

	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;

	/* refer to hw/block/virtio_blk.c */
	if (elem->out_num < 1 \|\| elem->in_num < 1) {
	error_report("virtio-blk request missing headers");
	goto err;
	}

	if (unlikely(iov_to_buf(out_iov, out_num, 0, &req->out,
	sizeof(req->out)) != sizeof(req->out))) {
	error_report("virtio-blk request outhdr too short");
	goto err;
	}

	iov_discard_front(&out_iov, &out_num, sizeof(req->out));

	if (in_iov[in_num - 1].iov_len < sizeof(struct virtio_blk_inhdr)) {
	error_report("virtio-blk request inhdr too short");
	goto err;
	}

	/* We always touch the last byte, so just see how big in_iov is. */
	req->in = (void *)in_iov[in_num - 1].iov_base
	+ in_iov[in_num - 1].iov_len
	- sizeof(struct virtio_blk_inhdr);
	iov_discard_back(in_iov, &in_num, sizeof(struct virtio_blk_inhdr));

	type = le32_to_cpu(req->out.type);
	switch (type & ~VIRTIO_BLK_T_BARRIER) {
	case VIRTIO_BLK_T_IN:
	case VIRTIO_BLK_T_OUT: {
	ssize_t ret = 0;
	bool is_write = type & VIRTIO_BLK_T_OUT;
	req->sector_num = le64_to_cpu(req->out.sector);

	if (is_write && !vexp->writable) {
	req->in->status = VIRTIO_BLK_S_IOERR;
	break;
	}

	int64_t offset = req->sector_num * vexp->blk_size;
	QEMUIOVector qiov;
	if (is_write) {
	qemu_iovec_init_external(&qiov, out_iov, out_num);
	ret = blk_co_pwritev(blk, offset, qiov.size, &qiov, 0);
	} else {
	qemu_iovec_init_external(&qiov, in_iov, in_num);
	ret = blk_co_preadv(blk, offset, qiov.size, &qiov, 0);
	}
	if (ret >= 0) {
	req->in->status = VIRTIO_BLK_S_OK;
	} else {
	req->in->status = VIRTIO_BLK_S_IOERR;
	}
	break;
	}
	case VIRTIO_BLK_T_FLUSH:
	if (blk_co_flush(blk) == 0) {
	req->in->status = VIRTIO_BLK_S_OK;
	} else {
	req->in->status = VIRTIO_BLK_S_IOERR;
	}
	break;
	case VIRTIO_BLK_T_GET_ID: {
	size_t size = MIN(iov_size(&elem->in_sg[0], in_num),
	VIRTIO_BLK_ID_BYTES);
	snprintf(elem->in_sg[0].iov_base, size, "%s", "vhost_user_blk");
	req->in->status = VIRTIO_BLK_S_OK;
	req->size = elem->in_sg[0].iov_len;
	break;
	}
	case VIRTIO_BLK_T_DISCARD:
	case VIRTIO_BLK_T_WRITE_ZEROES: {
	int rc;

	if (!vexp->writable) {
	req->in->status = VIRTIO_BLK_S_IOERR;
	break;
	}

	rc = vu_blk_discard_write_zeroes(blk, &elem->out_sg[1], out_num, type);
	if (rc == 0) {
	req->in->status = VIRTIO_BLK_S_OK;
	} else {
	req->in->status = VIRTIO_BLK_S_IOERR;
	}
	break;
	}
	default:
	req->in->status = VIRTIO_BLK_S_UNSUPP;
	break;
	}

	vu_blk_req_complete(req);
	return;

	err:
	free(req);
	}

	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);
	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->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 \|
	1ull << VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD;
	}

	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_MASTER) {
	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;

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

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

	vhost_user_server_detach_aio_context(&vexp->vu_server);
	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) >> BDRV_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(32768);
	config->max_discard_seg = cpu_to_le32(1);
	config->discard_sector_alignment = cpu_to_le32(config->blk_size >> 9);
	config->max_write_zeroes_sectors = cpu_to_le32(32768);
	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 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->writable = opts->writable;
	vexp->blkcfg.wce = 0;

	if (vu_opts->has_logical_block_size) {
	logical_block_size = vu_opts->logical_block_size;
	} else {
	logical_block_size = BDRV_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;
	}
	vexp->blk_size = logical_block_size;
	blk_set_guest_block_size(exp->blk, logical_block_size);

	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;
	}

	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);

	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);
	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);
	}

	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,
	};