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

 /*
  * QEMU Block driver for  NBD
  *
  * Copyright (C) 2008 Bull S.A.S.
  *     Author: Laurent Vivier <Laurent.Vivier@bull.net>
  *
  * Some parts:
  *    Copyright (C) 2007 Anthony Liguori <anthony@codemonkey.ws>
  *
  * 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 "nbd-client.h"
 #include "qemu/sockets.h"

 #define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
 #define INDEX_TO_HANDLE(bs, index)  ((index)  ^ ((uint64_t)(intptr_t)bs))

 static void nbd_recv_coroutines_enter_all(NbdClientSession *s)
 {
     int i;

     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
         if (s->recv_coroutine[i]) {
             qemu_coroutine_enter(s->recv_coroutine[i], NULL);
         }
     }
 }

 static void nbd_teardown_connection(NbdClientSession *client)
 {
     /* finish any pending coroutines */
     shutdown(client->sock, 2);
     nbd_recv_coroutines_enter_all(client);

     nbd_client_session_detach_aio_context(client);
     closesocket(client->sock);
     client->sock = -1;
 }

 static void nbd_reply_ready(void *opaque)
 {
     NbdClientSession *s = opaque;
     uint64_t i;
     int ret;

     if (s->reply.handle == 0) {
         /* No reply already in flight.  Fetch a header.  It is possible
          * that another thread has done the same thing in parallel, so
          * the socket is not readable anymore.
          */
         ret = nbd_receive_reply(s->sock, &s->reply);
         if (ret == -EAGAIN) {
             return;
         }
         if (ret < 0) {
             s->reply.handle = 0;
             goto fail;
         }
     }

     /* There's no need for a mutex on the receive side, because the
      * handler acts as a synchronization point and ensures that only
      * one coroutine is called until the reply finishes.  */
     i = HANDLE_TO_INDEX(s, s->reply.handle);
     if (i >= MAX_NBD_REQUESTS) {
         goto fail;
     }

     if (s->recv_coroutine[i]) {
         qemu_coroutine_enter(s->recv_coroutine[i], NULL);
         return;
     }

 fail:
     nbd_teardown_connection(s);
 }

 static void nbd_restart_write(void *opaque)
 {
     NbdClientSession *s = opaque;

     qemu_coroutine_enter(s->send_coroutine, NULL);
 }

 static int nbd_co_send_request(NbdClientSession *s,
     struct nbd_request *request,
     QEMUIOVector *qiov, int offset)
 {
     AioContext *aio_context;
     int rc, ret;

     qemu_co_mutex_lock(&s->send_mutex);
     s->send_coroutine = qemu_coroutine_self();
     aio_context = bdrv_get_aio_context(s->bs);
     aio_set_fd_handler(aio_context, s->sock,
                        nbd_reply_ready, nbd_restart_write, s);
     if (qiov) {
         if (!s->is_unix) {
             socket_set_cork(s->sock, 1);
         }
         rc = nbd_send_request(s->sock, request);
         if (rc >= 0) {
             ret = qemu_co_sendv(s->sock, qiov->iov, qiov->niov,
                                 offset, request->len);
             if (ret != request->len) {
                 rc = -EIO;
             }
         }
         if (!s->is_unix) {
             socket_set_cork(s->sock, 0);
         }
     } else {
         rc = nbd_send_request(s->sock, request);
     }
     aio_set_fd_handler(aio_context, s->sock, nbd_reply_ready, NULL, s);
     s->send_coroutine = NULL;
     qemu_co_mutex_unlock(&s->send_mutex);
     return rc;
 }

 static void nbd_co_receive_reply(NbdClientSession *s,
     struct nbd_request *request, struct nbd_reply *reply,
     QEMUIOVector *qiov, int offset)
 {
     int ret;

     /* Wait until we're woken up by the read handler.  TODO: perhaps
      * peek at the next reply and avoid yielding if it's ours?  */
     qemu_coroutine_yield();
     *reply = s->reply;
     if (reply->handle != request->handle) {
         reply->error = EIO;
     } else {
         if (qiov && reply->error == 0) {
             ret = qemu_co_recvv(s->sock, qiov->iov, qiov->niov,
                                 offset, request->len);
             if (ret != request->len) {
                 reply->error = EIO;
             }
         }

         /* Tell the read handler to read another header.  */
         s->reply.handle = 0;
     }
 }

 static void nbd_coroutine_start(NbdClientSession *s,
    struct nbd_request *request)
 {
     int i;

     /* Poor man semaphore.  The free_sema is locked when no other request
      * can be accepted, and unlocked after receiving one reply.  */
     if (s->in_flight >= MAX_NBD_REQUESTS - 1) {
         qemu_co_mutex_lock(&s->free_sema);
         assert(s->in_flight < MAX_NBD_REQUESTS);
     }
     s->in_flight++;

     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
         if (s->recv_coroutine[i] == NULL) {
             s->recv_coroutine[i] = qemu_coroutine_self();
             break;
         }
     }

     assert(i < MAX_NBD_REQUESTS);
     request->handle = INDEX_TO_HANDLE(s, i);
 }

 static void nbd_coroutine_end(NbdClientSession *s,
     struct nbd_request *request)
 {
     int i = HANDLE_TO_INDEX(s, request->handle);
     s->recv_coroutine[i] = NULL;
     if (s->in_flight-- == MAX_NBD_REQUESTS) {
         qemu_co_mutex_unlock(&s->free_sema);
     }
 }

 static int nbd_co_readv_1(NbdClientSession *client, int64_t sector_num,
                           int nb_sectors, QEMUIOVector *qiov,
                           int offset)
 {
     struct nbd_request request = { .type = NBD_CMD_READ };
     struct nbd_reply reply;
     ssize_t ret;

     request.from = sector_num * 512;
     request.len = nb_sectors * 512;

     nbd_coroutine_start(client, &request);
     ret = nbd_co_send_request(client, &request, NULL, 0);
     if (ret < 0) {
         reply.error = -ret;
     } else {
         nbd_co_receive_reply(client, &request, &reply, qiov, offset);
     }
     nbd_coroutine_end(client, &request);
     return -reply.error;

 }

 static int nbd_co_writev_1(NbdClientSession *client, int64_t sector_num,
                            int nb_sectors, QEMUIOVector *qiov,
                            int offset)
 {
     struct nbd_request request = { .type = NBD_CMD_WRITE };
     struct nbd_reply reply;
     ssize_t ret;

     if (!bdrv_enable_write_cache(client->bs) &&
         (client->nbdflags & NBD_FLAG_SEND_FUA)) {
         request.type |= NBD_CMD_FLAG_FUA;
     }

     request.from = sector_num * 512;
     request.len = nb_sectors * 512;

     nbd_coroutine_start(client, &request);
     ret = nbd_co_send_request(client, &request, qiov, offset);
     if (ret < 0) {
         reply.error = -ret;
     } else {
         nbd_co_receive_reply(client, &request, &reply, NULL, 0);
     }
     nbd_coroutine_end(client, &request);
     return -reply.error;
 }

 /* qemu-nbd has a limit of slightly less than 1M per request.  Try to
  * remain aligned to 4K. */
 #define NBD_MAX_SECTORS 2040

 int nbd_client_session_co_readv(NbdClientSession *client, int64_t sector_num,
     int nb_sectors, QEMUIOVector *qiov)
 {
     int offset = 0;
     int ret;
     while (nb_sectors > NBD_MAX_SECTORS) {
         ret = nbd_co_readv_1(client, sector_num,
                              NBD_MAX_SECTORS, qiov, offset);
         if (ret < 0) {
             return ret;
         }
         offset += NBD_MAX_SECTORS * 512;
         sector_num += NBD_MAX_SECTORS;
         nb_sectors -= NBD_MAX_SECTORS;
     }
     return nbd_co_readv_1(client, sector_num, nb_sectors, qiov, offset);
 }

 int nbd_client_session_co_writev(NbdClientSession *client, int64_t sector_num,
                                  int nb_sectors, QEMUIOVector *qiov)
 {
     int offset = 0;
     int ret;
     while (nb_sectors > NBD_MAX_SECTORS) {
         ret = nbd_co_writev_1(client, sector_num,
                               NBD_MAX_SECTORS, qiov, offset);
         if (ret < 0) {
             return ret;
         }
         offset += NBD_MAX_SECTORS * 512;
         sector_num += NBD_MAX_SECTORS;
         nb_sectors -= NBD_MAX_SECTORS;
     }
     return nbd_co_writev_1(client, sector_num, nb_sectors, qiov, offset);
 }

 int nbd_client_session_co_flush(NbdClientSession *client)
 {
     struct nbd_request request = { .type = NBD_CMD_FLUSH };
     struct nbd_reply reply;
     ssize_t ret;

     if (!(client->nbdflags & NBD_FLAG_SEND_FLUSH)) {
         return 0;
     }

     if (client->nbdflags & NBD_FLAG_SEND_FUA) {
         request.type |= NBD_CMD_FLAG_FUA;
     }

     request.from = 0;
     request.len = 0;

     nbd_coroutine_start(client, &request);
     ret = nbd_co_send_request(client, &request, NULL, 0);
     if (ret < 0) {
         reply.error = -ret;
     } else {
         nbd_co_receive_reply(client, &request, &reply, NULL, 0);
     }
     nbd_coroutine_end(client, &request);
     return -reply.error;
 }

 int nbd_client_session_co_discard(NbdClientSession *client, int64_t sector_num,
     int nb_sectors)
 {
     struct nbd_request request = { .type = NBD_CMD_TRIM };
     struct nbd_reply reply;
     ssize_t ret;

     if (!(client->nbdflags & NBD_FLAG_SEND_TRIM)) {
         return 0;
     }
     request.from = sector_num * 512;
     request.len = nb_sectors * 512;

     nbd_coroutine_start(client, &request);
     ret = nbd_co_send_request(client, &request, NULL, 0);
     if (ret < 0) {
         reply.error = -ret;
     } else {
         nbd_co_receive_reply(client, &request, &reply, NULL, 0);
     }
     nbd_coroutine_end(client, &request);
     return -reply.error;

 }

 void nbd_client_session_detach_aio_context(NbdClientSession *client)
 {
     aio_set_fd_handler(bdrv_get_aio_context(client->bs), client->sock,
                        NULL, NULL, NULL);
 }

 void nbd_client_session_attach_aio_context(NbdClientSession *client,
                                            AioContext *new_context)
 {
     aio_set_fd_handler(new_context, client->sock,
                        nbd_reply_ready, NULL, client);
 }

 void nbd_client_session_close(NbdClientSession *client)
 {
     struct nbd_request request = {
         .type = NBD_CMD_DISC,
         .from = 0,
         .len = 0
     };

     if (!client->bs) {
         return;
     }
     if (client->sock == -1) {
         return;
     }

     nbd_send_request(client->sock, &request);

     nbd_teardown_connection(client);
     client->bs = NULL;
 }

 int nbd_client_session_init(NbdClientSession *client, BlockDriverState *bs,
                             int sock, const char *export, Error **errp)
 {
     int ret;

     /* NBD handshake */
     logout("session init %s\n", export);
     qemu_set_block(sock);
     ret = nbd_receive_negotiate(sock, export,
                                 &client->nbdflags, &client->size,
                                 &client->blocksize, errp);
     if (ret < 0) {
         logout("Failed to negotiate with the NBD server\n");
         closesocket(sock);
         return ret;
     }

     qemu_co_mutex_init(&client->send_mutex);
     qemu_co_mutex_init(&client->free_sema);
     client->bs = bs;
     client->sock = sock;

     /* Now that we're connected, set the socket to be non-blocking and
      * kick the reply mechanism.  */
     qemu_set_nonblock(sock);
     nbd_client_session_attach_aio_context(client, bdrv_get_aio_context(bs));

     logout("Established connection with NBD server\n");
     return 0;
 }
	/*
	* QEMU Block driver for NBD
	*
	* Copyright (C) 2008 Bull S.A.S.
	* Author: Laurent Vivier <Laurent.Vivier@bull.net>
	*
	* Some parts:
	* Copyright (C) 2007 Anthony Liguori <anthony@codemonkey.ws>
	*
	* 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 "nbd-client.h"
	#include "qemu/sockets.h"

	#define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
	#define INDEX_TO_HANDLE(bs, index) ((index) ^ ((uint64_t)(intptr_t)bs))

	static void nbd_recv_coroutines_enter_all(NbdClientSession *s)
	{
	int i;

	for (i = 0; i < MAX_NBD_REQUESTS; i++) {
	if (s->recv_coroutine[i]) {
	qemu_coroutine_enter(s->recv_coroutine[i], NULL);
	}
	}
	}

	static void nbd_teardown_connection(NbdClientSession *client)
	{
	/* finish any pending coroutines */
	shutdown(client->sock, 2);
	nbd_recv_coroutines_enter_all(client);

	nbd_client_session_detach_aio_context(client);
	closesocket(client->sock);
	client->sock = -1;
	}

	static void nbd_reply_ready(void *opaque)
	{
	NbdClientSession *s = opaque;
	uint64_t i;
	int ret;

	if (s->reply.handle == 0) {
	/* No reply already in flight. Fetch a header. It is possible
	* that another thread has done the same thing in parallel, so
	* the socket is not readable anymore.
	*/
	ret = nbd_receive_reply(s->sock, &s->reply);
	if (ret == -EAGAIN) {
	return;
	}
	if (ret < 0) {
	s->reply.handle = 0;
	goto fail;
	}
	}

	/* There's no need for a mutex on the receive side, because the
	* handler acts as a synchronization point and ensures that only
	* one coroutine is called until the reply finishes. */
	i = HANDLE_TO_INDEX(s, s->reply.handle);
	if (i >= MAX_NBD_REQUESTS) {
	goto fail;
	}

	if (s->recv_coroutine[i]) {
	qemu_coroutine_enter(s->recv_coroutine[i], NULL);
	return;
	}

	fail:
	nbd_teardown_connection(s);
	}

	static void nbd_restart_write(void *opaque)
	{
	NbdClientSession *s = opaque;

	qemu_coroutine_enter(s->send_coroutine, NULL);
	}

	static int nbd_co_send_request(NbdClientSession *s,
	struct nbd_request *request,
	QEMUIOVector *qiov, int offset)
	{
	AioContext *aio_context;
	int rc, ret;

	qemu_co_mutex_lock(&s->send_mutex);
	s->send_coroutine = qemu_coroutine_self();
	aio_context = bdrv_get_aio_context(s->bs);
	aio_set_fd_handler(aio_context, s->sock,
	nbd_reply_ready, nbd_restart_write, s);
	if (qiov) {
	if (!s->is_unix) {
	socket_set_cork(s->sock, 1);
	}
	rc = nbd_send_request(s->sock, request);
	if (rc >= 0) {
	ret = qemu_co_sendv(s->sock, qiov->iov, qiov->niov,
	offset, request->len);
	if (ret != request->len) {
	rc = -EIO;
	}
	}
	if (!s->is_unix) {
	socket_set_cork(s->sock, 0);
	}
	} else {
	rc = nbd_send_request(s->sock, request);
	}
	aio_set_fd_handler(aio_context, s->sock, nbd_reply_ready, NULL, s);
	s->send_coroutine = NULL;
	qemu_co_mutex_unlock(&s->send_mutex);
	return rc;
	}

	static void nbd_co_receive_reply(NbdClientSession *s,
	struct nbd_request request, struct nbd_reply reply,
	QEMUIOVector *qiov, int offset)
	{
	int ret;

	/* Wait until we're woken up by the read handler. TODO: perhaps
	* peek at the next reply and avoid yielding if it's ours? */
	qemu_coroutine_yield();
	*reply = s->reply;
	if (reply->handle != request->handle) {
	reply->error = EIO;
	} else {
	if (qiov && reply->error == 0) {
	ret = qemu_co_recvv(s->sock, qiov->iov, qiov->niov,
	offset, request->len);
	if (ret != request->len) {
	reply->error = EIO;
	}
	}

	/* Tell the read handler to read another header. */
	s->reply.handle = 0;
	}
	}

	static void nbd_coroutine_start(NbdClientSession *s,
	struct nbd_request *request)
	{
	int i;

	/* Poor man semaphore. The free_sema is locked when no other request
	* can be accepted, and unlocked after receiving one reply. */
	if (s->in_flight >= MAX_NBD_REQUESTS - 1) {
	qemu_co_mutex_lock(&s->free_sema);
	assert(s->in_flight < MAX_NBD_REQUESTS);
	}
	s->in_flight++;

	for (i = 0; i < MAX_NBD_REQUESTS; i++) {
	if (s->recv_coroutine[i] == NULL) {
	s->recv_coroutine[i] = qemu_coroutine_self();
	break;
	}
	}

	assert(i < MAX_NBD_REQUESTS);
	request->handle = INDEX_TO_HANDLE(s, i);
	}

	static void nbd_coroutine_end(NbdClientSession *s,
	struct nbd_request *request)
	{
	int i = HANDLE_TO_INDEX(s, request->handle);
	s->recv_coroutine[i] = NULL;
	if (s->in_flight-- == MAX_NBD_REQUESTS) {
	qemu_co_mutex_unlock(&s->free_sema);
	}
	}

	static int nbd_co_readv_1(NbdClientSession *client, int64_t sector_num,
	int nb_sectors, QEMUIOVector *qiov,
	int offset)
	{
	struct nbd_request request = { .type = NBD_CMD_READ };
	struct nbd_reply reply;
	ssize_t ret;

	request.from = sector_num * 512;
	request.len = nb_sectors * 512;

	nbd_coroutine_start(client, &request);
	ret = nbd_co_send_request(client, &request, NULL, 0);
	if (ret < 0) {
	reply.error = -ret;
	} else {
	nbd_co_receive_reply(client, &request, &reply, qiov, offset);
	}
	nbd_coroutine_end(client, &request);
	return -reply.error;

	}

	static int nbd_co_writev_1(NbdClientSession *client, int64_t sector_num,
	int nb_sectors, QEMUIOVector *qiov,
	int offset)
	{
	struct nbd_request request = { .type = NBD_CMD_WRITE };
	struct nbd_reply reply;
	ssize_t ret;

	if (!bdrv_enable_write_cache(client->bs) &&
	(client->nbdflags & NBD_FLAG_SEND_FUA)) {
	request.type \|= NBD_CMD_FLAG_FUA;
	}

	request.from = sector_num * 512;
	request.len = nb_sectors * 512;

	nbd_coroutine_start(client, &request);
	ret = nbd_co_send_request(client, &request, qiov, offset);
	if (ret < 0) {
	reply.error = -ret;
	} else {
	nbd_co_receive_reply(client, &request, &reply, NULL, 0);
	}
	nbd_coroutine_end(client, &request);
	return -reply.error;
	}

	/* qemu-nbd has a limit of slightly less than 1M per request. Try to
	* remain aligned to 4K. */
	#define NBD_MAX_SECTORS 2040

	int nbd_client_session_co_readv(NbdClientSession *client, int64_t sector_num,
	int nb_sectors, QEMUIOVector *qiov)
	{
	int offset = 0;
	int ret;
	while (nb_sectors > NBD_MAX_SECTORS) {
	ret = nbd_co_readv_1(client, sector_num,
	NBD_MAX_SECTORS, qiov, offset);
	if (ret < 0) {
	return ret;
	}
	offset += NBD_MAX_SECTORS * 512;
	sector_num += NBD_MAX_SECTORS;
	nb_sectors -= NBD_MAX_SECTORS;
	}
	return nbd_co_readv_1(client, sector_num, nb_sectors, qiov, offset);
	}

	int nbd_client_session_co_writev(NbdClientSession *client, int64_t sector_num,
	int nb_sectors, QEMUIOVector *qiov)
	{
	int offset = 0;
	int ret;
	while (nb_sectors > NBD_MAX_SECTORS) {
	ret = nbd_co_writev_1(client, sector_num,
	NBD_MAX_SECTORS, qiov, offset);
	if (ret < 0) {
	return ret;
	}
	offset += NBD_MAX_SECTORS * 512;
	sector_num += NBD_MAX_SECTORS;
	nb_sectors -= NBD_MAX_SECTORS;
	}
	return nbd_co_writev_1(client, sector_num, nb_sectors, qiov, offset);
	}

	int nbd_client_session_co_flush(NbdClientSession *client)
	{
	struct nbd_request request = { .type = NBD_CMD_FLUSH };
	struct nbd_reply reply;
	ssize_t ret;

	if (!(client->nbdflags & NBD_FLAG_SEND_FLUSH)) {
	return 0;
	}

	if (client->nbdflags & NBD_FLAG_SEND_FUA) {
	request.type \|= NBD_CMD_FLAG_FUA;
	}

	request.from = 0;
	request.len = 0;

	nbd_coroutine_start(client, &request);
	ret = nbd_co_send_request(client, &request, NULL, 0);
	if (ret < 0) {
	reply.error = -ret;
	} else {
	nbd_co_receive_reply(client, &request, &reply, NULL, 0);
	}
	nbd_coroutine_end(client, &request);
	return -reply.error;
	}

	int nbd_client_session_co_discard(NbdClientSession *client, int64_t sector_num,
	int nb_sectors)
	{
	struct nbd_request request = { .type = NBD_CMD_TRIM };
	struct nbd_reply reply;
	ssize_t ret;

	if (!(client->nbdflags & NBD_FLAG_SEND_TRIM)) {
	return 0;
	}
	request.from = sector_num * 512;
	request.len = nb_sectors * 512;

	nbd_coroutine_start(client, &request);
	ret = nbd_co_send_request(client, &request, NULL, 0);
	if (ret < 0) {
	reply.error = -ret;
	} else {
	nbd_co_receive_reply(client, &request, &reply, NULL, 0);
	}
	nbd_coroutine_end(client, &request);
	return -reply.error;

	}

	void nbd_client_session_detach_aio_context(NbdClientSession *client)
	{
	aio_set_fd_handler(bdrv_get_aio_context(client->bs), client->sock,
	NULL, NULL, NULL);
	}

	void nbd_client_session_attach_aio_context(NbdClientSession *client,
	AioContext *new_context)
	{
	aio_set_fd_handler(new_context, client->sock,
	nbd_reply_ready, NULL, client);
	}

	void nbd_client_session_close(NbdClientSession *client)
	{
	struct nbd_request request = {
	.type = NBD_CMD_DISC,
	.from = 0,
	.len = 0
	};

	if (!client->bs) {
	return;
	}
	if (client->sock == -1) {
	return;
	}

	nbd_send_request(client->sock, &request);

	nbd_teardown_connection(client);
	client->bs = NULL;
	}

	int nbd_client_session_init(NbdClientSession client, BlockDriverState bs,
	int sock, const char export, Error *errp)
	{
	int ret;

	/* NBD handshake */
	logout("session init %s\n", export);
	qemu_set_block(sock);
	ret = nbd_receive_negotiate(sock, export,
	&client->nbdflags, &client->size,
	&client->blocksize, errp);
	if (ret < 0) {
	logout("Failed to negotiate with the NBD server\n");
	closesocket(sock);
	return ret;
	}

	qemu_co_mutex_init(&client->send_mutex);
	qemu_co_mutex_init(&client->free_sema);
	client->bs = bs;
	client->sock = sock;

	/* Now that we're connected, set the socket to be non-blocking and
	* kick the reply mechanism. */
	qemu_set_nonblock(sock);
	nbd_client_session_attach_aio_context(client, bdrv_get_aio_context(bs));

	logout("Established connection with NBD server\n");
	return 0;
	}