Archipelago » qemu

/*

 *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>

 *

 *  Network Block Device

 *

 *  This program is free software; you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation; under version 2 of the License.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program; if not, see <http://www.gnu.org/licenses/>.

 */

#include "nbd.h"

#include "block.h"

#include "block_int.h"

#include "qemu-coroutine.h"

#include <errno.h>

#include <string.h>

#ifndef _WIN32

#include <sys/ioctl.h>

#endif

#if defined(__sun__) || defined(__HAIKU__)

#include <sys/ioccom.h>

#endif

#include <ctype.h>

#include <inttypes.h>

#ifdef __linux__

#include <linux/fs.h>

#endif

#include "qemu_socket.h"

#include "qemu-queue.h"

//#define DEBUG_NBD

#ifdef DEBUG_NBD

#define TRACE(msg, ...) do { \

    LOG(msg, ## __VA_ARGS__); \

} while(0)

#else

#define TRACE(msg, ...) \

    do { } while (0)

#endif

#define LOG(msg, ...) do { \

    fprintf(stderr, "%s:%s():L%d: " msg "\n", \

            __FILE__, __FUNCTION__, __LINE__, ## __VA_ARGS__); \

} while(0)

/* This is all part of the "official" NBD API */

#define NBD_REPLY_SIZE          (4 + 4 + 8)

#define NBD_REQUEST_MAGIC       0x25609513

#define NBD_REPLY_MAGIC         0x67446698

#define NBD_SET_SOCK            _IO(0xab, 0)

#define NBD_SET_BLKSIZE         _IO(0xab, 1)

#define NBD_SET_SIZE            _IO(0xab, 2)

#define NBD_DO_IT               _IO(0xab, 3)

#define NBD_CLEAR_SOCK          _IO(0xab, 4)

#define NBD_CLEAR_QUE           _IO(0xab, 5)

#define NBD_PRINT_DEBUG         _IO(0xab, 6)

#define NBD_SET_SIZE_BLOCKS     _IO(0xab, 7)

#define NBD_DISCONNECT          _IO(0xab, 8)

#define NBD_SET_TIMEOUT         _IO(0xab, 9)

#define NBD_SET_FLAGS           _IO(0xab, 10)

#define NBD_OPT_EXPORT_NAME     (1 << 0)

/* That's all folks */

#define read_sync(fd, buffer, size) nbd_wr_sync(fd, buffer, size, true)

#define write_sync(fd, buffer, size) nbd_wr_sync(fd, buffer, size, false)

size_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read)

{

    size_t offset = 0;

    if (qemu_in_coroutine()) {

        if (do_read) {

            return qemu_co_recv(fd, buffer, size);

        } else {

            return qemu_co_send(fd, buffer, size);

        }

    }

    while (offset < size) {

        ssize_t len;

        if (do_read) {

            len = qemu_recv(fd, buffer + offset, size - offset, 0);

        } else {

            len = send(fd, buffer + offset, size - offset, 0);

        }

        if (len == -1)

            errno = socket_error();

        /* recoverable error */

        if (len == -1 && (errno == EAGAIN || errno == EINTR)) {

            continue;

        }

        /* eof */

        if (len == 0) {

            break;

        }

        /* unrecoverable error */

        if (len == -1) {

            return 0;

        }

        offset += len;

    }

    return offset;

}

static void combine_addr(char *buf, size_t len, const char* address,

                         uint16_t port)

{

    /* If the address-part contains a colon, it's an IPv6 IP so needs [] */

    if (strstr(address, ":")) {

        snprintf(buf, len, "[%s]:%u", address, port);

    } else {

        snprintf(buf, len, "%s:%u", address, port);

    }

}

int tcp_socket_outgoing(const char *address, uint16_t port)

{

    char address_and_port[128];

    combine_addr(address_and_port, 128, address, port);

    return tcp_socket_outgoing_spec(address_and_port);

}

int tcp_socket_outgoing_spec(const char *address_and_port)

{

    return inet_connect(address_and_port, SOCK_STREAM);

}

int tcp_socket_incoming(const char *address, uint16_t port)

{

    char address_and_port[128];

    combine_addr(address_and_port, 128, address, port);

    return tcp_socket_incoming_spec(address_and_port);

}

int tcp_socket_incoming_spec(const char *address_and_port)

{

    char *ostr  = NULL;

    int olen = 0;

    return inet_listen(address_and_port, ostr, olen, SOCK_STREAM, 0);

}

int unix_socket_incoming(const char *path)

{

    char *ostr = NULL;

    int olen = 0;

    return unix_listen(path, ostr, olen);

}

int unix_socket_outgoing(const char *path)

{

    return unix_connect(path);

}

/* Basic flow

   Server         Client

   Negotiate

                  Request

   Response

                  Request

   Response

                  ...

   ...

                  Request (type == 2)

*/

static int nbd_send_negotiate(int csock, off_t size, uint32_t flags)

{

    char buf[8 + 8 + 8 + 128];

    /* Negotiate

        [ 0 ..   7]   passwd   ("NBDMAGIC")

        [ 8 ..  15]   magic    (0x00420281861253)

        [16 ..  23]   size

        [24 ..  27]   flags

        [28 .. 151]   reserved (0)

     */

    TRACE("Beginning negotiation.");

    memcpy(buf, "NBDMAGIC", 8);

    cpu_to_be64w((uint64_t*)(buf + 8), 0x00420281861253LL);

    cpu_to_be64w((uint64_t*)(buf + 16), size);

    cpu_to_be32w((uint32_t*)(buf + 24),

                 flags | NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |

                 NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA);

    memset(buf + 28, 0, 124);

    if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {

        LOG("write failed");

        errno = EINVAL;

        return -1;

    }

    TRACE("Negotiation succeeded.");

    return 0;

}

int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,

                          off_t *size, size_t *blocksize)

{

    char buf[256];

    uint64_t magic, s;

    uint16_t tmp;

    TRACE("Receiving negotiation.");

    if (read_sync(csock, buf, 8) != 8) {

        LOG("read failed");

        errno = EINVAL;

        return -1;

    }

    buf[8] = '\0';

    if (strlen(buf) == 0) {

        LOG("server connection closed");

        errno = EINVAL;

        return -1;

    }

    TRACE("Magic is %c%c%c%c%c%c%c%c",

          qemu_isprint(buf[0]) ? buf[0] : '.',

          qemu_isprint(buf[1]) ? buf[1] : '.',

          qemu_isprint(buf[2]) ? buf[2] : '.',

          qemu_isprint(buf[3]) ? buf[3] : '.',

          qemu_isprint(buf[4]) ? buf[4] : '.',

          qemu_isprint(buf[5]) ? buf[5] : '.',

          qemu_isprint(buf[6]) ? buf[6] : '.',

          qemu_isprint(buf[7]) ? buf[7] : '.');

    if (memcmp(buf, "NBDMAGIC", 8) != 0) {

        LOG("Invalid magic received");

        errno = EINVAL;

        return -1;

    }

    if (read_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {

        LOG("read failed");

        errno = EINVAL;

        return -1;

    }

    magic = be64_to_cpu(magic);

    TRACE("Magic is 0x%" PRIx64, magic);

    if (name) {

        uint32_t reserved = 0;

        uint32_t opt;

        uint32_t namesize;

        TRACE("Checking magic (opts_magic)");

        if (magic != 0x49484156454F5054LL) {

            LOG("Bad magic received");

            errno = EINVAL;

            return -1;

        }

        if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {

            LOG("flags read failed");

            errno = EINVAL;

            return -1;

        }

        *flags = be16_to_cpu(tmp) << 16;

        /* reserved for future use */

        if (write_sync(csock, &reserved, sizeof(reserved)) !=

            sizeof(reserved)) {

            LOG("write failed (reserved)");

            errno = EINVAL;

            return -1;

        }

        /* write the export name */

        magic = cpu_to_be64(magic);

        if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {

            LOG("write failed (magic)");

            errno = EINVAL;

            return -1;

        }

        opt = cpu_to_be32(NBD_OPT_EXPORT_NAME);

        if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {

            LOG("write failed (opt)");

            errno = EINVAL;

            return -1;

        }

        namesize = cpu_to_be32(strlen(name));

        if (write_sync(csock, &namesize, sizeof(namesize)) !=

            sizeof(namesize)) {

            LOG("write failed (namesize)");

            errno = EINVAL;

            return -1;

        }

        if (write_sync(csock, (char*)name, strlen(name)) != strlen(name)) {

            LOG("write failed (name)");

            errno = EINVAL;

            return -1;

        }

    } else {

        TRACE("Checking magic (cli_magic)");

        if (magic != 0x00420281861253LL) {

            LOG("Bad magic received");

            errno = EINVAL;

            return -1;

        }

    }

    if (read_sync(csock, &s, sizeof(s)) != sizeof(s)) {

        LOG("read failed");

        errno = EINVAL;

        return -1;

    }

    *size = be64_to_cpu(s);

    *blocksize = 1024;

    TRACE("Size is %" PRIu64, *size);

    if (!name) {

        if (read_sync(csock, flags, sizeof(*flags)) != sizeof(*flags)) {

            LOG("read failed (flags)");

            errno = EINVAL;

            return -1;

        }

        *flags = be32_to_cpup(flags);

    } else {

        if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {

            LOG("read failed (tmp)");

            errno = EINVAL;

            return -1;

        }

        *flags |= be32_to_cpu(tmp);

    }

    if (read_sync(csock, &buf, 124) != 124) {

        LOG("read failed (buf)");

        errno = EINVAL;

        return -1;

    }

        return 0;

}

#ifdef __linux__

int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize)

{

    TRACE("Setting NBD socket");

    if (ioctl(fd, NBD_SET_SOCK, csock) == -1) {

        int serrno = errno;

        LOG("Failed to set NBD socket");

        errno = serrno;

        return -1;

    }

    TRACE("Setting block size to %lu", (unsigned long)blocksize);

    if (ioctl(fd, NBD_SET_BLKSIZE, blocksize) == -1) {

        int serrno = errno;

        LOG("Failed setting NBD block size");

        errno = serrno;

        return -1;

    }

        TRACE("Setting size to %zd block(s)", (size_t)(size / blocksize));

    if (ioctl(fd, NBD_SET_SIZE_BLOCKS, size / blocksize) == -1) {

        int serrno = errno;

        LOG("Failed setting size (in blocks)");

        errno = serrno;

        return -1;

    }

    if (flags & NBD_FLAG_READ_ONLY) {

        int read_only = 1;

        TRACE("Setting readonly attribute");

        if (ioctl(fd, BLKROSET, (unsigned long) &read_only) < 0) {

            int serrno = errno;

            LOG("Failed setting read-only attribute");

            errno = serrno;

            return -1;

        }

    }

    if (ioctl(fd, NBD_SET_FLAGS, flags) < 0

        && errno != ENOTTY) {

        int serrno = errno;

        LOG("Failed setting flags");

        errno = serrno;

        return -1;

    }

    TRACE("Negotiation ended");

    return 0;

}

int nbd_disconnect(int fd)

{

    ioctl(fd, NBD_CLEAR_QUE);

    ioctl(fd, NBD_DISCONNECT);

    ioctl(fd, NBD_CLEAR_SOCK);

    return 0;

}

int nbd_client(int fd)

{

    int ret;

    int serrno;

    TRACE("Doing NBD loop");

    ret = ioctl(fd, NBD_DO_IT);

    if (ret == -1 && errno == EPIPE) {

        /* NBD_DO_IT normally returns EPIPE when someone has disconnected

         * the socket via NBD_DISCONNECT.  We do not want to return 1 in

         * that case.

         */

        ret = 0;

    }

    serrno = errno;

    TRACE("NBD loop returned %d: %s", ret, strerror(serrno));

    TRACE("Clearing NBD queue");

    ioctl(fd, NBD_CLEAR_QUE);

    TRACE("Clearing NBD socket");

    ioctl(fd, NBD_CLEAR_SOCK);

    errno = serrno;

    return ret;

}

#else

int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize)

{

    errno = ENOTSUP;

    return -1;

}

int nbd_disconnect(int fd)

{

    errno = ENOTSUP;

    return -1;

}

int nbd_client(int fd)

{

    errno = ENOTSUP;

    return -1;

}

#endif

int nbd_send_request(int csock, struct nbd_request *request)

{

    uint8_t buf[4 + 4 + 8 + 8 + 4];

    cpu_to_be32w((uint32_t*)buf, NBD_REQUEST_MAGIC);

    cpu_to_be32w((uint32_t*)(buf + 4), request->type);

    cpu_to_be64w((uint64_t*)(buf + 8), request->handle);

    cpu_to_be64w((uint64_t*)(buf + 16), request->from);

    cpu_to_be32w((uint32_t*)(buf + 24), request->len);

    TRACE("Sending request to client: "

          "{ .from = %" PRIu64", .len = %u, .handle = %" PRIu64", .type=%i}",

          request->from, request->len, request->handle, request->type);

    if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {

        LOG("writing to socket failed");

        errno = EINVAL;

        return -1;

    }

    return 0;

}

static int nbd_receive_request(int csock, struct nbd_request *request)

{

    uint8_t buf[4 + 4 + 8 + 8 + 4];

    uint32_t magic;

    if (read_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {

        LOG("read failed");

        errno = EINVAL;

        return -1;

    }

    /* Request

       [ 0 ..  3]   magic   (NBD_REQUEST_MAGIC)

       [ 4 ..  7]   type    (0 == READ, 1 == WRITE)

       [ 8 .. 15]   handle

       [16 .. 23]   from

       [24 .. 27]   len

     */

    magic = be32_to_cpup((uint32_t*)buf);

    request->type  = be32_to_cpup((uint32_t*)(buf + 4));

    request->handle = be64_to_cpup((uint64_t*)(buf + 8));

    request->from  = be64_to_cpup((uint64_t*)(buf + 16));

    request->len   = be32_to_cpup((uint32_t*)(buf + 24));

    TRACE("Got request: "

          "{ magic = 0x%x, .type = %d, from = %" PRIu64" , len = %u }",

          magic, request->type, request->from, request->len);

    if (magic != NBD_REQUEST_MAGIC) {

        LOG("invalid magic (got 0x%x)", magic);

        errno = EINVAL;

        return -1;

    }

    return 0;

}

int nbd_receive_reply(int csock, struct nbd_reply *reply)

{

    uint8_t buf[NBD_REPLY_SIZE];

    uint32_t magic;

    memset(buf, 0xAA, sizeof(buf));

    if (read_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {

        LOG("read failed");

        errno = EINVAL;

        return -1;

    }

    /* Reply

       [ 0 ..  3]    magic   (NBD_REPLY_MAGIC)

       [ 4 ..  7]    error   (0 == no error)

       [ 7 .. 15]    handle

     */

    magic = be32_to_cpup((uint32_t*)buf);

    reply->error  = be32_to_cpup((uint32_t*)(buf + 4));

    reply->handle = be64_to_cpup((uint64_t*)(buf + 8));

    TRACE("Got reply: "

          "{ magic = 0x%x, .error = %d, handle = %" PRIu64" }",

          magic, reply->error, reply->handle);

    if (magic != NBD_REPLY_MAGIC) {

        LOG("invalid magic (got 0x%x)", magic);

        errno = EINVAL;

        return -1;

    }

    return 0;

}

static int nbd_send_reply(int csock, struct nbd_reply *reply)

{

    uint8_t buf[4 + 4 + 8];

    /* Reply

       [ 0 ..  3]    magic   (NBD_REPLY_MAGIC)

       [ 4 ..  7]    error   (0 == no error)

       [ 7 .. 15]    handle

     */

    cpu_to_be32w((uint32_t*)buf, NBD_REPLY_MAGIC);

    cpu_to_be32w((uint32_t*)(buf + 4), reply->error);

    cpu_to_be64w((uint64_t*)(buf + 8), reply->handle);

    TRACE("Sending response to client");

    if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {

        LOG("writing to socket failed");

        errno = EINVAL;

        return -1;

    }

    return 0;

}

#define MAX_NBD_REQUESTS 16

typedef struct NBDRequest NBDRequest;

struct NBDRequest {

    QSIMPLEQ_ENTRY(NBDRequest) entry;

    NBDClient *client;

    uint8_t *data;

};

struct NBDExport {

    BlockDriverState *bs;

    off_t dev_offset;

    off_t size;

    uint32_t nbdflags;

    QSIMPLEQ_HEAD(, NBDRequest) requests;

};

struct NBDClient {

    int refcount;

    void (*close)(NBDClient *client);

    NBDExport *exp;

    int sock;

    Coroutine *recv_coroutine;

    CoMutex send_lock;

    Coroutine *send_coroutine;

    int nb_requests;

};

static void nbd_client_get(NBDClient *client)

{

    client->refcount++;

}

static void nbd_client_put(NBDClient *client)

{

    if (--client->refcount == 0) {

        g_free(client);

    }

}

static void nbd_client_close(NBDClient *client)

{

    qemu_set_fd_handler2(client->sock, NULL, NULL, NULL, NULL);

    close(client->sock);

    client->sock = -1;

    if (client->close) {

        client->close(client);

    }

    nbd_client_put(client);

}

static NBDRequest *nbd_request_get(NBDClient *client)

{

    NBDRequest *req;

    NBDExport *exp = client->exp;

    assert(client->nb_requests <= MAX_NBD_REQUESTS - 1);

    client->nb_requests++;

    if (QSIMPLEQ_EMPTY(&exp->requests)) {

        req = g_malloc0(sizeof(NBDRequest));

        req->data = qemu_blockalign(exp->bs, NBD_BUFFER_SIZE);

    } else {

        req = QSIMPLEQ_FIRST(&exp->requests);

        QSIMPLEQ_REMOVE_HEAD(&exp->requests, entry);

    }

    nbd_client_get(client);

    req->client = client;

    return req;

}

static void nbd_request_put(NBDRequest *req)

{

    NBDClient *client = req->client;

    QSIMPLEQ_INSERT_HEAD(&client->exp->requests, req, entry);

    if (client->nb_requests-- == MAX_NBD_REQUESTS) {

        qemu_notify_event();

    }

    nbd_client_put(client);

}

NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,

                          off_t size, uint32_t nbdflags)

{

    NBDExport *exp = g_malloc0(sizeof(NBDExport));

    QSIMPLEQ_INIT(&exp->requests);

    exp->bs = bs;

    exp->dev_offset = dev_offset;

    exp->nbdflags = nbdflags;

    exp->size = size == -1 ? exp->bs->total_sectors * 512 : size;

    return exp;

}

void nbd_export_close(NBDExport *exp)

{

    while (!QSIMPLEQ_EMPTY(&exp->requests)) {

        NBDRequest *first = QSIMPLEQ_FIRST(&exp->requests);

        QSIMPLEQ_REMOVE_HEAD(&exp->requests, entry);

        qemu_vfree(first->data);

        g_free(first);

    }

    bdrv_close(exp->bs);

    g_free(exp);

}

static int nbd_can_read(void *opaque);

static void nbd_read(void *opaque);

static void nbd_restart_write(void *opaque);

static int nbd_co_send_reply(NBDRequest *req, struct nbd_reply *reply,

                             int len)

{

    NBDClient *client = req->client;

    int csock = client->sock;

    int rc, ret;

    qemu_co_mutex_lock(&client->send_lock);

    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read,

                         nbd_restart_write, client);

    client->send_coroutine = qemu_coroutine_self();

    if (!len) {

        rc = nbd_send_reply(csock, reply);

        if (rc == -1) {

            rc = -errno;

        }

    } else {

        socket_set_cork(csock, 1);

        rc = nbd_send_reply(csock, reply);

        if (rc != -1) {

            ret = qemu_co_send(csock, req->data, len);

            if (ret != len) {

                errno = EIO;

                rc = -1;

            }

        }

        if (rc == -1) {

            rc = -errno;

        }

        socket_set_cork(csock, 0);

    }

    client->send_coroutine = NULL;

    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read, NULL, client);

    qemu_co_mutex_unlock(&client->send_lock);

    return rc;

}

static int nbd_co_receive_request(NBDRequest *req, struct nbd_request *request)

{

    NBDClient *client = req->client;

    int csock = client->sock;

    int rc;

    client->recv_coroutine = qemu_coroutine_self();

    if (nbd_receive_request(csock, request) == -1) {

        rc = -EIO;

        goto out;

    }

    if (request->len > NBD_BUFFER_SIZE) {

        LOG("len (%u) is larger than max len (%u)",

            request->len, NBD_BUFFER_SIZE);

        rc = -EINVAL;

        goto out;

    }

    if ((request->from + request->len) < request->from) {

        LOG("integer overflow detected! "

            "you're probably being attacked");

        rc = -EINVAL;

        goto out;

    }

    TRACE("Decoding type");

    if ((request->type & NBD_CMD_MASK_COMMAND) == NBD_CMD_WRITE) {

        TRACE("Reading %u byte(s)", request->len);

        if (qemu_co_recv(csock, req->data, request->len) != request->len) {

            LOG("reading from socket failed");

            rc = -EIO;

            goto out;

        }

    }

    rc = 0;

out:

    client->recv_coroutine = NULL;

    return rc;

}

static void nbd_trip(void *opaque)

{

    NBDClient *client = opaque;

    NBDRequest *req = nbd_request_get(client);

    NBDExport *exp = client->exp;

    struct nbd_request request;

    struct nbd_reply reply;

    int ret;

    TRACE("Reading request.");

    ret = nbd_co_receive_request(req, &request);

    if (ret == -EIO) {

        goto out;

    }

    reply.handle = request.handle;

    reply.error = 0;

    if (ret < 0) {

        reply.error = -ret;

        goto error_reply;

    }

    if ((request.from + request.len) > exp->size) {

            LOG("From: %" PRIu64 ", Len: %u, Size: %" PRIu64

            ", Offset: %" PRIu64 "\n",

                    request.from, request.len,

                    (uint64_t)exp->size, exp->dev_offset);

        LOG("requested operation past EOF--bad client?");

        goto invalid_request;

    }

    switch (request.type & NBD_CMD_MASK_COMMAND) {

    case NBD_CMD_READ:

        TRACE("Request type is READ");

        ret = bdrv_read(exp->bs, (request.from + exp->dev_offset) / 512,

                        req->data, request.len / 512);

        if (ret < 0) {

            LOG("reading from file failed");

            reply.error = -ret;

            goto error_reply;

        }

        TRACE("Read %u byte(s)", request.len);

        if (nbd_co_send_reply(req, &reply, request.len) < 0)

            goto out;

        break;

    case NBD_CMD_WRITE:

        TRACE("Request type is WRITE");

        if (exp->nbdflags & NBD_FLAG_READ_ONLY) {

            TRACE("Server is read-only, return error");

            reply.error = EROFS;

            goto error_reply;

        }

        TRACE("Writing to device");

        ret = bdrv_write(exp->bs, (request.from + exp->dev_offset) / 512,

                         req->data, request.len / 512);

        if (ret < 0) {

            LOG("writing to file failed");

            reply.error = -ret;

            goto error_reply;

        }

        if (request.type & NBD_CMD_FLAG_FUA) {

            ret = bdrv_co_flush(exp->bs);

            if (ret < 0) {

                LOG("flush failed");

                reply.error = -ret;

                goto error_reply;

            }

        }

        if (nbd_co_send_reply(req, &reply, 0) < 0)

            goto out;

        break;

    case NBD_CMD_DISC: