nbd: Split nbd.c

We have NBD server code and client code, all mixed in a file. Now split
them into separate files under nbd/, and update MAINTAINERS.

filter_nbd for iotest 083 is updated to keep the log filtered out.

Signed-off-by: Fam Zheng <famz@redhat.com>
Message-Id: <1452760863-25350-3-git-send-email-famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

5 files changed, 1591 insertions, 0 deletions

diff --git a/nbd/Makefile.objs b/nbd/Makefile.objs
new file mode 100644
index 0000000000..eb3dd4461d
--- /dev/null
+++ b/nbd/Makefile.objs
@@ -0,0 +1 @@
+block-obj-y += server.o client.o common.o
diff --git a/nbd/client.c b/nbd/client.c
new file mode 100644
index 0000000000..83df7ba378
--- /dev/null
+++ b/nbd/client.c
@@ -0,0 +1,361 @@
+/*
+ *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
+ *
+ *  Network Block Device Client Side
+ *
+ *  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-internal.h"
+
+static int nbd_errno_to_system_errno(int err)
+{
+    switch (err) {
+    case NBD_SUCCESS:
+        return 0;
+    case NBD_EPERM:
+        return EPERM;
+    case NBD_EIO:
+        return EIO;
+    case NBD_ENOMEM:
+        return ENOMEM;
+    case NBD_ENOSPC:
+        return ENOSPC;
+    case NBD_EINVAL:
+    default:
+        return EINVAL;
+    }
+}
+
+/* Definitions for opaque data types */
+
+static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
+
+/* That's all folks */
+
+/* Basic flow for negotiation
+
+   Server         Client
+   Negotiate
+
+   or
+
+   Server         Client
+   Negotiate #1
+                  Option
+   Negotiate #2
+
+   ----
+
+   followed by
+
+   Server         Client
+                  Request
+   Response
+                  Request
+   Response
+                  ...
+   ...
+                  Request (type == 2)
+
+*/
+
+int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
+                          off_t *size, Error **errp)
+{
+    char buf[256];
+    uint64_t magic, s;
+    uint16_t tmp;
+    int rc;
+
+    TRACE("Receiving negotiation.");
+
+    rc = -EINVAL;
+
+    if (read_sync(csock, buf, 8) != 8) {
+        error_setg(errp, "Failed to read data");
+        goto fail;
+    }
+
+    buf[8] = '\0';
+    if (strlen(buf) == 0) {
+        error_setg(errp, "Server connection closed unexpectedly");
+        goto fail;
+    }
+
+    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) {
+        error_setg(errp, "Invalid magic received");
+        goto fail;
+    }
+
+    if (read_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+        error_setg(errp, "Failed to read magic");
+        goto fail;
+    }
+    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 != NBD_OPTS_MAGIC) {
+            if (magic == NBD_CLIENT_MAGIC) {
+                error_setg(errp, "Server does not support export names");
+            } else {
+                error_setg(errp, "Bad magic received");
+            }
+            goto fail;
+        }
+        if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+            error_setg(errp, "Failed to read server flags");
+            goto fail;
+        }
+        *flags = be16_to_cpu(tmp) << 16;
+        /* reserved for future use */
+        if (write_sync(csock, &reserved, sizeof(reserved)) !=
+            sizeof(reserved)) {
+            error_setg(errp, "Failed to read reserved field");
+            goto fail;
+        }
+        /* write the export name */
+        magic = cpu_to_be64(magic);
+        if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+            error_setg(errp, "Failed to send export name magic");
+            goto fail;
+        }
+        opt = cpu_to_be32(NBD_OPT_EXPORT_NAME);
+        if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {
+            error_setg(errp, "Failed to send export name option number");
+            goto fail;
+        }
+        namesize = cpu_to_be32(strlen(name));
+        if (write_sync(csock, &namesize, sizeof(namesize)) !=
+            sizeof(namesize)) {
+            error_setg(errp, "Failed to send export name length");
+            goto fail;
+        }
+        if (write_sync(csock, (char*)name, strlen(name)) != strlen(name)) {
+            error_setg(errp, "Failed to send export name");
+            goto fail;
+        }
+    } else {
+        TRACE("Checking magic (cli_magic)");
+
+        if (magic != NBD_CLIENT_MAGIC) {
+            if (magic == NBD_OPTS_MAGIC) {
+                error_setg(errp, "Server requires an export name");
+            } else {
+                error_setg(errp, "Bad magic received");
+            }
+            goto fail;
+        }
+    }
+
+    if (read_sync(csock, &s, sizeof(s)) != sizeof(s)) {
+        error_setg(errp, "Failed to read export length");
+        goto fail;
+    }
+    *size = be64_to_cpu(s);
+    TRACE("Size is %" PRIu64, *size);
+
+    if (!name) {
+        if (read_sync(csock, flags, sizeof(*flags)) != sizeof(*flags)) {
+            error_setg(errp, "Failed to read export flags");
+            goto fail;
+        }
+        *flags = be32_to_cpup(flags);
+    } else {
+        if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+            error_setg(errp, "Failed to read export flags");
+            goto fail;
+        }
+        *flags |= be16_to_cpu(tmp);
+    }
+    if (read_sync(csock, &buf, 124) != 124) {
+        error_setg(errp, "Failed to read reserved block");
+        goto fail;
+    }
+    rc = 0;
+
+fail:
+    return rc;
+}
+
+#ifdef __linux__
+int nbd_init(int fd, int csock, uint32_t flags, off_t size)
+{
+    TRACE("Setting NBD socket");
+
+    if (ioctl(fd, NBD_SET_SOCK, csock) < 0) {
+        int serrno = errno;
+        LOG("Failed to set NBD socket");
+        return -serrno;
+    }
+
+    TRACE("Setting block size to %lu", (unsigned long)BDRV_SECTOR_SIZE);
+
+    if (ioctl(fd, NBD_SET_BLKSIZE, (size_t)BDRV_SECTOR_SIZE) < 0) {
+        int serrno = errno;
+        LOG("Failed setting NBD block size");
+        return -serrno;
+    }
+
+    TRACE("Setting size to %zd block(s)", (size_t)(size / BDRV_SECTOR_SIZE));
+
+    if (ioctl(fd, NBD_SET_SIZE_BLOCKS, (size_t)(size / BDRV_SECTOR_SIZE)) < 0) {
+        int serrno = errno;
+        LOG("Failed setting size (in blocks)");
+        return -serrno;
+    }
+
+    if (ioctl(fd, NBD_SET_FLAGS, flags) < 0) {
+        if (errno == ENOTTY) {
+            int read_only = (flags & NBD_FLAG_READ_ONLY) != 0;
+            TRACE("Setting readonly attribute");
+
+            if (ioctl(fd, BLKROSET, (unsigned long) &read_only) < 0) {
+                int serrno = errno;
+                LOG("Failed setting read-only attribute");
+                return -serrno;
+            }
+        } else {
+            int serrno = errno;
+            LOG("Failed setting flags");
+            return -serrno;
+        }
+    }
+
+    TRACE("Negotiation ended");
+
+    return 0;
+}
+
+int nbd_client(int fd)
+{
+    int ret;
+    int serrno;
+
+    TRACE("Doing NBD loop");
+
+    ret = ioctl(fd, NBD_DO_IT);
+    if (ret < 0 && 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)
+{
+    return -ENOTSUP;
+}
+
+int nbd_client(int fd)
+{
+    return -ENOTSUP;
+}
+#endif
+
+ssize_t nbd_send_request(int csock, struct nbd_request *request)
+{
+    uint8_t buf[NBD_REQUEST_SIZE];
+    ssize_t ret;
+
+    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);
+
+    ret = write_sync(csock, buf, sizeof(buf));
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret != sizeof(buf)) {
+        LOG("writing to socket failed");
+        return -EINVAL;
+    }
+    return 0;
+}
+
+ssize_t nbd_receive_reply(int csock, struct nbd_reply *reply)
+{
+    uint8_t buf[NBD_REPLY_SIZE];
+    uint32_t magic;
+    ssize_t ret;
+
+    ret = read_sync(csock, buf, sizeof(buf));
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret != sizeof(buf)) {
+        LOG("read failed");
+        return -EINVAL;
+    }
+
+    /* 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));
+
+    reply->error = nbd_errno_to_system_errno(reply->error);
+
+    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);
+        return -EINVAL;
+    }
+    return 0;
+}
+
diff --git a/nbd/common.c b/nbd/common.c
new file mode 100644
index 0000000000..7b089b0f3b
--- /dev/null
+++ b/nbd/common.c
@@ -0,0 +1,64 @@
+/*
+ *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
+ *
+ *  Network Block Device Common Code
+ *
+ *  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-internal.h"
+
+ssize_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read)
+{
+    size_t offset = 0;
+    int err;
+
+    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 < 0) {
+            err = socket_error();
+
+            /* recoverable error */
+            if (err == EINTR || (offset > 0 && (err == EAGAIN || err == EWOULDBLOCK))) {
+                continue;
+            }
+
+            /* unrecoverable error */
+            return -err;
+        }
+
+        /* eof */
+        if (len == 0) {
+            break;
+        }
+
+        offset += len;
+    }
+
+    return offset;
+}
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
new file mode 100644
index 0000000000..c0a657575b
--- /dev/null
+++ b/nbd/nbd-internal.h
@@ -0,0 +1,113 @@
+/*
+ * NBD Internal Declarations
+ *
+ * Copyright (C) 2016 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.
+ */
+
+#ifndef NBD_INTERNAL_H
+#define NBD_INTERNAL_H
+#include "block/nbd.h"
+#include "sysemu/block-backend.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/sockets.h"
+#include "qemu/queue.h"
+#include "qemu/main-loop.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.
+ *
+ * The most up-to-date documentation is available at:
+ * https://github.com/yoe/nbd/blob/master/doc/proto.txt
+ */
+
+#define NBD_REQUEST_SIZE        (4 + 4 + 8 + 8 + 4)
+#define NBD_REPLY_SIZE          (4 + 4 + 8)
+#define NBD_REQUEST_MAGIC       0x25609513
+#define NBD_REPLY_MAGIC         0x67446698
+#define NBD_OPTS_MAGIC          0x49484156454F5054LL
+#define NBD_CLIENT_MAGIC        0x0000420281861253LL
+#define NBD_REP_MAGIC           0x3e889045565a9LL
+
+#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)
+#define NBD_OPT_ABORT           (2)
+#define NBD_OPT_LIST            (3)
+
+/* NBD errors are based on errno numbers, so there is a 1:1 mapping,
+ * but only a limited set of errno values is specified in the protocol.
+ * Everything else is squashed to EINVAL.
+ */
+#define NBD_SUCCESS    0
+#define NBD_EPERM      1
+#define NBD_EIO        5
+#define NBD_ENOMEM     12
+#define NBD_EINVAL     22
+#define NBD_ENOSPC     28
+
+static inline ssize_t read_sync(int fd, void *buffer, size_t size)
+{
+    /* Sockets are kept in blocking mode in the negotiation phase.  After
+     * that, a non-readable socket simply means that another thread stole
+     * our request/reply.  Synchronization is done with recv_coroutine, so
+     * that this is coroutine-safe.
+     */
+    return nbd_wr_sync(fd, buffer, size, true);
+}
+
+static inline ssize_t write_sync(int fd, void *buffer, size_t size)
+{
+    int ret;
+    do {
+        /* For writes, we do expect the socket to be writable.  */
+        ret = nbd_wr_sync(fd, buffer, size, false);
+    } while (ret == -EAGAIN);
+    return ret;
+}
+
+#endif
diff --git a/nbd/server.c b/nbd/server.c
new file mode 100644
index 0000000000..ba25ce3604
--- /dev/null
+++ b/nbd/server.c
@@ -0,0 +1,1052 @@
+/*
+ *  Copyright (C) 2005  Anthony Liguori <anthony@codemonkey.ws>
+ *
+ *  Network Block Device Server Side
+ *
+ *  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-internal.h"
+
+static int system_errno_to_nbd_errno(int err)
+{
+    switch (err) {
+    case 0:
+        return NBD_SUCCESS;
+    case EPERM:
+        return NBD_EPERM;
+    case EIO:
+        return NBD_EIO;
+    case ENOMEM:
+        return NBD_ENOMEM;
+#ifdef EDQUOT
+    case EDQUOT:
+#endif
+    case EFBIG:
+    case ENOSPC:
+        return NBD_ENOSPC;
+    case EINVAL:
+    default:
+        return NBD_EINVAL;
+    }
+}
+
+/* Definitions for opaque data types */
+
+typedef struct NBDRequest NBDRequest;
+
+struct NBDRequest {
+    QSIMPLEQ_ENTRY(NBDRequest) entry;
+    NBDClient *client;
+    uint8_t *data;
+};
+
+struct NBDExport {
+    int refcount;
+    void (*close)(NBDExport *exp);
+
+    BlockBackend *blk;
+    char *name;
+    off_t dev_offset;
+    off_t size;
+    uint32_t nbdflags;
+    QTAILQ_HEAD(, NBDClient) clients;
+    QTAILQ_ENTRY(NBDExport) next;
+
+    AioContext *ctx;
+};
+
+static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
+
+struct NBDClient {
+    int refcount;
+    void (*close)(NBDClient *client);
+
+    NBDExport *exp;
+    int sock;
+
+    Coroutine *recv_coroutine;
+
+    CoMutex send_lock;
+    Coroutine *send_coroutine;
+
+    bool can_read;
+
+    QTAILQ_ENTRY(NBDClient) next;
+    int nb_requests;
+    bool closing;
+};
+
+/* That's all folks */
+
+static void nbd_set_handlers(NBDClient *client);
+static void nbd_unset_handlers(NBDClient *client);
+static void nbd_update_can_read(NBDClient *client);
+
+static ssize_t drop_sync(int fd, size_t size)
+{
+    ssize_t ret, dropped = size;
+    uint8_t *buffer = g_malloc(MIN(65536, size));
+
+    while (size > 0) {
+        ret = read_sync(fd, buffer, MIN(65536, size));
+        if (ret < 0) {
+            g_free(buffer);
+            return ret;
+        }
+
+        assert(ret <= size);
+        size -= ret;
+    }
+
+    g_free(buffer);
+    return dropped;
+}
+
+/* Basic flow for negotiation
+
+   Server         Client
+   Negotiate
+
+   or
+
+   Server         Client
+   Negotiate #1
+                  Option
+   Negotiate #2
+
+   ----
+
+   followed by
+
+   Server         Client
+                  Request
+   Response
+                  Request
+   Response
+                  ...
+   ...
+                  Request (type == 2)
+
+*/
+
+static int nbd_send_rep(int csock, uint32_t type, uint32_t opt)
+{
+    uint64_t magic;
+    uint32_t len;
+
+    magic = cpu_to_be64(NBD_REP_MAGIC);
+    if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+        LOG("write failed (rep magic)");
+        return -EINVAL;
+    }
+    opt = cpu_to_be32(opt);
+    if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {
+        LOG("write failed (rep opt)");
+        return -EINVAL;
+    }
+    type = cpu_to_be32(type);
+    if (write_sync(csock, &type, sizeof(type)) != sizeof(type)) {
+        LOG("write failed (rep type)");
+        return -EINVAL;
+    }
+    len = cpu_to_be32(0);
+    if (write_sync(csock, &len, sizeof(len)) != sizeof(len)) {
+        LOG("write failed (rep data length)");
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static int nbd_send_rep_list(int csock, NBDExport *exp)
+{
+    uint64_t magic, name_len;
+    uint32_t opt, type, len;
+
+    name_len = strlen(exp->name);
+    magic = cpu_to_be64(NBD_REP_MAGIC);
+    if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+        LOG("write failed (magic)");
+        return -EINVAL;
+     }
+    opt = cpu_to_be32(NBD_OPT_LIST);
+    if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {
+        LOG("write failed (opt)");
+        return -EINVAL;
+    }
+    type = cpu_to_be32(NBD_REP_SERVER);
+    if (write_sync(csock, &type, sizeof(type)) != sizeof(type)) {
+        LOG("write failed (reply type)");
+        return -EINVAL;
+    }
+    len = cpu_to_be32(name_len + sizeof(len));
+    if (write_sync(csock, &len, sizeof(len)) != sizeof(len)) {
+        LOG("write failed (length)");
+        return -EINVAL;
+    }
+    len = cpu_to_be32(name_len);
+    if (write_sync(csock, &len, sizeof(len)) != sizeof(len)) {
+        LOG("write failed (length)");
+        return -EINVAL;
+    }
+    if (write_sync(csock, exp->name, name_len) != name_len) {
+        LOG("write failed (buffer)");
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static int nbd_handle_list(NBDClient *client, uint32_t length)
+{
+    int csock;
+    NBDExport *exp;
+
+    csock = client->sock;
+    if (length) {
+        if (drop_sync(csock, length) != length) {
+            return -EIO;
+        }
+        return nbd_send_rep(csock, NBD_REP_ERR_INVALID, NBD_OPT_LIST);
+    }
+
+    /* For each export, send a NBD_REP_SERVER reply. */
+    QTAILQ_FOREACH(exp, &exports, next) {
+        if (nbd_send_rep_list(csock, exp)) {
+            return -EINVAL;
+        }
+    }
+    /* Finish with a NBD_REP_ACK. */
+    return nbd_send_rep(csock, NBD_REP_ACK, NBD_OPT_LIST);
+}
+
+static int nbd_handle_export_name(NBDClient *client, uint32_t length)
+{
+    int rc = -EINVAL, csock = client->sock;
+    char name[256];
+
+    /* Client sends:
+        [20 ..  xx]   export name (length bytes)
+     */
+    TRACE("Checking length");
+    if (length > 255) {
+        LOG("Bad length received");
+        goto fail;
+    }
+    if (read_sync(csock, name, length) != length) {
+        LOG("read failed");
+        goto fail;
+    }
+    name[length] = '\0';
+
+    client->exp = nbd_export_find(name);
+    if (!client->exp) {
+        LOG("export not found");
+        goto fail;
+    }
+
+    QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
+    nbd_export_get(client->exp);
+    rc = 0;
+fail:
+    return rc;
+}
+
+static int nbd_receive_options(NBDClient *client)
+{
+    int csock = client->sock;
+    uint32_t flags;
+
+    /* Client sends:
+        [ 0 ..   3]   client flags
+
+        [ 0 ..   7]   NBD_OPTS_MAGIC
+        [ 8 ..  11]   NBD option
+        [12 ..  15]   Data length
+        ...           Rest of request
+
+        [ 0 ..   7]   NBD_OPTS_MAGIC
+        [ 8 ..  11]   Second NBD option
+        [12 ..  15]   Data length
+        ...           Rest of request
+    */
+
+    if (read_sync(csock, &flags, sizeof(flags)) != sizeof(flags)) {
+        LOG("read failed");
+        return -EIO;
+    }
+    TRACE("Checking client flags");
+    be32_to_cpus(&flags);
+    if (flags != 0 && flags != NBD_FLAG_C_FIXED_NEWSTYLE) {
+        LOG("Bad client flags received");
+        return -EIO;
+    }
+
+    while (1) {
+        int ret;
+        uint32_t tmp, length;
+        uint64_t magic;
+
+        if (read_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+            LOG("read failed");
+            return -EINVAL;
+        }
+        TRACE("Checking opts magic");
+        if (magic != be64_to_cpu(NBD_OPTS_MAGIC)) {
+            LOG("Bad magic received");
+            return -EINVAL;
+        }
+
+        if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+            LOG("read failed");
+            return -EINVAL;
+        }
+
+        if (read_sync(csock, &length, sizeof(length)) != sizeof(length)) {
+            LOG("read failed");
+            return -EINVAL;
+        }
+        length = be32_to_cpu(length);
+
+        TRACE("Checking option");
+        switch (be32_to_cpu(tmp)) {
+        case NBD_OPT_LIST:
+            ret = nbd_handle_list(client, length);
+            if (ret < 0) {
+                return ret;
+            }
+            break;
+
+        case NBD_OPT_ABORT:
+            return -EINVAL;
+
+        case NBD_OPT_EXPORT_NAME:
+            return nbd_handle_export_name(client, length);
+
+        default:
+            tmp = be32_to_cpu(tmp);
+            LOG("Unsupported option 0x%x", tmp);
+            nbd_send_rep(client->sock, NBD_REP_ERR_UNSUP, tmp);
+            return -EINVAL;
+        }
+    }
+}
+
+static int nbd_send_negotiate(NBDClient *client)
+{
+    int csock = client->sock;
+    char buf[8 + 8 + 8 + 128];
+    int rc;
+    const int myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
+                         NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA);
+
+    /* Negotiation header without options:
+        [ 0 ..   7]   passwd       ("NBDMAGIC")
+        [ 8 ..  15]   magic        (NBD_CLIENT_MAGIC)
+        [16 ..  23]   size
+        [24 ..  25]   server flags (0)
+        [26 ..  27]   export flags
+        [28 .. 151]   reserved     (0)
+
+       Negotiation header with options, part 1:
+        [ 0 ..   7]   passwd       ("NBDMAGIC")
+        [ 8 ..  15]   magic        (NBD_OPTS_MAGIC)
+        [16 ..  17]   server flags (0)
+
+       part 2 (after options are sent):
+        [18 ..  25]   size
+        [26 ..  27]   export flags
+        [28 .. 151]   reserved     (0)
+     */
+
+    qemu_set_block(csock);
+    rc = -EINVAL;
+
+    TRACE("Beginning negotiation.");
+    memset(buf, 0, sizeof(buf));
+    memcpy(buf, "NBDMAGIC", 8);
+    if (client->exp) {
+        assert ((client->exp->nbdflags & ~65535) == 0);
+        cpu_to_be64w((uint64_t*)(buf + 8), NBD_CLIENT_MAGIC);
+        cpu_to_be64w((uint64_t*)(buf + 16), client->exp->size);
+        cpu_to_be16w((uint16_t*)(buf + 26), client->exp->nbdflags | myflags);
+    } else {
+        cpu_to_be64w((uint64_t*)(buf + 8), NBD_OPTS_MAGIC);
+        cpu_to_be16w((uint16_t *)(buf + 16), NBD_FLAG_FIXED_NEWSTYLE);
+    }
+
+    if (client->exp) {
+        if (write_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {
+            LOG("write failed");
+            goto fail;
+        }
+    } else {
+        if (write_sync(csock, buf, 18) != 18) {
+            LOG("write failed");
+            goto fail;
+        }
+        rc = nbd_receive_options(client);
+        if (rc != 0) {
+            LOG("option negotiation failed");
+            goto fail;
+        }
+
+        assert ((client->exp->nbdflags & ~65535) == 0);
+        cpu_to_be64w((uint64_t*)(buf + 18), client->exp->size);
+        cpu_to_be16w((uint16_t*)(buf + 26), client->exp->nbdflags | myflags);
+        if (write_sync(csock, buf + 18, sizeof(buf) - 18) != sizeof(buf) - 18) {
+            LOG("write failed");
+            goto fail;
+        }
+    }
+
+    TRACE("Negotiation succeeded.");
+    rc = 0;
+fail:
+    qemu_set_nonblock(csock);
+    return rc;
+}
+
+#ifdef __linux__
+
+int nbd_disconnect(int fd)
+{
+    ioctl(fd, NBD_CLEAR_QUE);
+    ioctl(fd, NBD_DISCONNECT);
+    ioctl(fd, NBD_CLEAR_SOCK);
+    return 0;
+}
+
+#else
+
+int nbd_disconnect(int fd)
+{
+    return -ENOTSUP;
+}
+#endif
+
+static ssize_t nbd_receive_request(int csock, struct nbd_request *request)
+{
+    uint8_t buf[NBD_REQUEST_SIZE];
+    uint32_t magic;
+    ssize_t ret;
+
+    ret = read_sync(csock, buf, sizeof(buf));
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret != sizeof(buf)) {
+        LOG("read failed");
+        return -EINVAL;
+    }
+
+    /* 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);
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static ssize_t nbd_send_reply(int csock, struct nbd_reply *reply)
+{
+    uint8_t buf[NBD_REPLY_SIZE];
+    ssize_t ret;
+
+    reply->error = system_errno_to_nbd_errno(reply->error);
+
+    /* 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");
+
+    ret = write_sync(csock, buf, sizeof(buf));
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret != sizeof(buf)) {
+        LOG("writing to socket failed");
+        return -EINVAL;
+    }
+    return 0;
+}
+
+#define MAX_NBD_REQUESTS 16
+
+void nbd_client_get(NBDClient *client)
+{
+    client->refcount++;
+}
+
+void nbd_client_put(NBDClient *client)
+{
+    if (--client->refcount == 0) {
+        /* The last reference should be dropped by client->close,
+         * which is called by client_close.
+         */
+        assert(client->closing);
+
+        nbd_unset_handlers(client);
+        close(client->sock);
+        client->sock = -1;
+        if (client->exp) {
+            QTAILQ_REMOVE(&client->exp->clients, client, next);
+            nbd_export_put(client->exp);
+        }
+        g_free(client);
+    }
+}
+
+static void client_close(NBDClient *client)
+{
+    if (client->closing) {
+        return;
+    }
+
+    client->closing = true;
+
+    /* Force requests to finish.  They will drop their own references,
+     * then we'll close the socket and free the NBDClient.
+     */
+    shutdown(client->sock, 2);
+
+    /* Also tell the client, so that they release their reference.  */
+    if (client->close) {
+        client->close(client);
+    }
+}
+
+static NBDRequest *nbd_request_get(NBDClient *client)
+{
+    NBDRequest *req;
+
+    assert(client->nb_requests <= MAX_NBD_REQUESTS - 1);
+    client->nb_requests++;
+    nbd_update_can_read(client);
+
+    req = g_new0(NBDRequest, 1);
+    nbd_client_get(client);
+    req->client = client;
+    return req;
+}
+
+static void nbd_request_put(NBDRequest *req)
+{
+    NBDClient *client = req->client;
+
+    if (req->data) {
+        qemu_vfree(req->data);
+    }
+    g_free(req);
+
+    client->nb_requests--;
+    nbd_update_can_read(client);
+    nbd_client_put(client);
+}
+
+static void blk_aio_attached(AioContext *ctx, void *opaque)
+{
+    NBDExport *exp = opaque;
+    NBDClient *client;
+
+    TRACE("Export %s: Attaching clients to AIO context %p\n", exp->name, ctx);
+
+    exp->ctx = ctx;
+
+    QTAILQ_FOREACH(client, &exp->clients, next) {
+        nbd_set_handlers(client);
+    }
+}
+
+static void blk_aio_detach(void *opaque)
+{
+    NBDExport *exp = opaque;
+    NBDClient *client;
+
+    TRACE("Export %s: Detaching clients from AIO context %p\n", exp->name, exp->ctx);
+
+    QTAILQ_FOREACH(client, &exp->clients, next) {
+        nbd_unset_handlers(client);
+    }
+
+    exp->ctx = NULL;
+}
+
+NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
+                          uint32_t nbdflags, void (*close)(NBDExport *),
+                          Error **errp)
+{
+    NBDExport *exp = g_malloc0(sizeof(NBDExport));
+    exp->refcount = 1;
+    QTAILQ_INIT(&exp->clients);
+    exp->blk = blk;
+    exp->dev_offset = dev_offset;
+    exp->nbdflags = nbdflags;
+    exp->size = size < 0 ? blk_getlength(blk) : size;
+    if (exp->size < 0) {
+        error_setg_errno(errp, -exp->size,
+                         "Failed to determine the NBD export's length");
+        goto fail;
+    }
+    exp->size -= exp->size % BDRV_SECTOR_SIZE;
+
+    exp->close = close;
+    exp->ctx = blk_get_aio_context(blk);
+    blk_ref(blk);
+    blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
+    /*
+     * NBD exports are used for non-shared storage migration.  Make sure
+     * that BDRV_O_INCOMING is cleared and the image is ready for write
+     * access since the export could be available before migration handover.
+     */
+    blk_invalidate_cache(blk, NULL);
+    return exp;
+
+fail:
+    g_free(exp);
+    return NULL;
+}
+
+NBDExport *nbd_export_find(const char *name)
+{
+    NBDExport *exp;
+    QTAILQ_FOREACH(exp, &exports, next) {
+        if (strcmp(name, exp->name) == 0) {
+            return exp;
+        }
+    }
+
+    return NULL;
+}
+
+void nbd_export_set_name(NBDExport *exp, const char *name)
+{
+    if (exp->name == name) {
+        return;
+    }
+
+    nbd_export_get(exp);
+    if (exp->name != NULL) {
+        g_free(exp->name);
+        exp->name = NULL;
+        QTAILQ_REMOVE(&exports, exp, next);
+        nbd_export_put(exp);
+    }
+    if (name != NULL) {
+        nbd_export_get(exp);
+        exp->name = g_strdup(name);
+        QTAILQ_INSERT_TAIL(&exports, exp, next);
+    }
+    nbd_export_put(exp);
+}
+
+void nbd_export_close(NBDExport *exp)
+{
+    NBDClient *client, *next;
+
+    nbd_export_get(exp);
+    QTAILQ_FOREACH_SAFE(client, &exp->clients, next, next) {
+        client_close(client);
+    }
+    nbd_export_set_name(exp, NULL);
+    nbd_export_put(exp);
+}
+
+void nbd_export_get(NBDExport *exp)
+{
+    assert(exp->refcount > 0);
+    exp->refcount++;
+}
+
+void nbd_export_put(NBDExport *exp)
+{
+    assert(exp->refcount > 0);
+    if (exp->refcount == 1) {
+        nbd_export_close(exp);
+    }
+
+    if (--exp->refcount == 0) {
+        assert(exp->name == NULL);
+
+        if (exp->close) {
+            exp->close(exp);
+        }
+
+        if (exp->blk) {
+            blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
+                                            blk_aio_detach, exp);
+            blk_unref(exp->blk);
+            exp->blk = NULL;
+        }
+
+        g_free(exp);
+    }
+}
+
+BlockBackend *nbd_export_get_blockdev(NBDExport *exp)
+{
+    return exp->blk;
+}
+
+void nbd_export_close_all(void)
+{
+    NBDExport *exp, *next;
+
+    QTAILQ_FOREACH_SAFE(exp, &exports, next, next) {
+        nbd_export_close(exp);
+    }
+}
+
+static ssize_t nbd_co_send_reply(NBDRequest *req, struct nbd_reply *reply,
+                                 int len)
+{
+    NBDClient *client = req->client;
+    int csock = client->sock;
+    ssize_t rc, ret;
+
+    qemu_co_mutex_lock(&client->send_lock);
+    client->send_coroutine = qemu_coroutine_self();
+    nbd_set_handlers(client);
+
+    if (!len) {
+        rc = nbd_send_reply(csock, reply);
+    } else {
+        socket_set_cork(csock, 1);
+        rc = nbd_send_reply(csock, reply);
+        if (rc >= 0) {
+            ret = qemu_co_send(csock, req->data, len);
+            if (ret != len) {
+                rc = -EIO;
+            }
+        }
+        socket_set_cork(csock, 0);
+    }
+
+    client->send_coroutine = NULL;
+    nbd_set_handlers(client);
+    qemu_co_mutex_unlock(&client->send_lock);
+    return rc;
+}
+
+static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *request)
+{
+    NBDClient *client = req->client;
+    int csock = client->sock;
+    uint32_t command;
+    ssize_t rc;
+
+    client->recv_coroutine = qemu_coroutine_self();
+    nbd_update_can_read(client);
+
+    rc = nbd_receive_request(csock, request);
+    if (rc < 0) {
+        if (rc != -EAGAIN) {
+            rc = -EIO;
+        }
+        goto out;
+    }
+
+    if (request->len > NBD_MAX_BUFFER_SIZE) {
+        LOG("len (%u) is larger than max len (%u)",
+            request->len, NBD_MAX_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");
+
+    command = request->type & NBD_CMD_MASK_COMMAND;
+    if (command == NBD_CMD_READ || command == NBD_CMD_WRITE) {
+        req->data = blk_blockalign(client->exp->blk, request->len);
+    }
+    if (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;
+    nbd_update_can_read(client);
+
+    return rc;
+}
+
+static void nbd_trip(void *opaque)
+{
+    NBDClient *client = opaque;
+    NBDExport *exp = client->exp;
+    NBDRequest *req;
+    struct nbd_request request;
+    struct nbd_reply reply;
+    ssize_t ret;
+    uint32_t command;
+
+    TRACE("Reading request.");
+    if (client->closing) {
+        return;
+    }
+
+    req = nbd_request_get(client);
+    ret = nbd_co_receive_request(req, &request);
+    if (ret == -EAGAIN) {
+        goto done;
+    }
+    if (ret == -EIO) {
+        goto out;
+    }
+
+    reply.handle = request.handle;
+    reply.error = 0;
+
+    if (ret < 0) {
+        reply.error = -ret;
+        goto error_reply;
+    }
+    command = request.type & NBD_CMD_MASK_COMMAND;
+    if (command != NBD_CMD_DISC && (request.from + request.len) > exp->size) {
+            LOG("From: %" PRIu64 ", Len: %u, Size: %" PRIu64
+            ", Offset: %" PRIu64 "\n",
+                    request.from, request.len,
+                    (uint64_t)exp->size, (uint64_t)exp->dev_offset);
+        LOG("requested operation past EOF--bad client?");
+        goto invalid_request;
+    }
+
+    if (client->closing) {
+        /*
+         * The client may be closed when we are blocked in
+         * nbd_co_receive_request()
+         */
+        goto done;
+    }
+
+    switch (command) {
+    case NBD_CMD_READ:
+        TRACE("Request type is READ");
+
+        if (request.type & NBD_CMD_FLAG_FUA) {
+            ret = blk_co_flush(exp->blk);
+            if (ret < 0) {
+                LOG("flush failed");
+                reply.error = -ret;
+                goto error_reply;
+            }
+        }
+
+        ret = blk_read(exp->blk,
+                       (request.from + exp->dev_offset) / BDRV_SECTOR_SIZE,
+                       req->data, request.len / BDRV_SECTOR_SIZE);
+        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 = blk_write(exp->blk,
+                        (request.from + exp->dev_offset) / BDRV_SECTOR_SIZE,
+                        req->data, request.len / BDRV_SECTOR_SIZE);
+        if (ret < 0) {
+            LOG("writing to file failed");
+            reply.error = -ret;
+            goto error_reply;
+        }
+
+        if (request.type & NBD_CMD_FLAG_FUA) {
+            ret = blk_co_flush(exp->blk);
+            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:
+        TRACE("Request type is DISCONNECT");
+        errno = 0;
+        goto out;
+    case NBD_CMD_FLUSH:
+        TRACE("Request type is FLUSH");
+
+        ret = blk_co_flush(exp->blk);
+        if (ret < 0) {
+            LOG("flush failed");
+            reply.error = -ret;
+        }
+        if (nbd_co_send_reply(req, &reply, 0) < 0) {
+            goto out;
+        }
+        break;
+    case NBD_CMD_TRIM:
+        TRACE("Request type is TRIM");
+        ret = blk_co_discard(exp->blk, (request.from + exp->dev_offset)
+                                       / BDRV_SECTOR_SIZE,
+                             request.len / BDRV_SECTOR_SIZE);
+        if (ret < 0) {
+            LOG("discard failed");
+            reply.error = -ret;
+        }
+        if (nbd_co_send_reply(req, &reply, 0) < 0) {
+            goto out;
+        }
+        break;
+    default:
+        LOG("invalid request type (%u) received", request.type);
+    invalid_request:
+        reply.error = EINVAL;
+    error_reply:
+        if (nbd_co_send_reply(req, &reply, 0) < 0) {
+            goto out;
+        }
+        break;
+    }
+
+    TRACE("Request/Reply complete");
+
+done:
+    nbd_request_put(req);
+    return;
+
+out:
+    nbd_request_put(req);
+    client_close(client);
+}
+
+static void nbd_read(void *opaque)
+{
+    NBDClient *client = opaque;
+
+    if (client->recv_coroutine) {
+        qemu_coroutine_enter(client->recv_coroutine, NULL);
+    } else {
+        qemu_coroutine_enter(qemu_coroutine_create(nbd_trip), client);
+    }
+}
+
+static void nbd_restart_write(void *opaque)
+{
+    NBDClient *client = opaque;
+
+    qemu_coroutine_enter(client->send_coroutine, NULL);
+}
+
+static void nbd_set_handlers(NBDClient *client)
+{
+    if (client->exp && client->exp->ctx) {
+        aio_set_fd_handler(client->exp->ctx, client->sock,
+                           true,
+                           client->can_read ? nbd_read : NULL,
+                           client->send_coroutine ? nbd_restart_write : NULL,
+                           client);
+    }
+}
+
+static void nbd_unset_handlers(NBDClient *client)
+{
+    if (client->exp && client->exp->ctx) {
+        aio_set_fd_handler(client->exp->ctx, client->sock,
+                           true, NULL, NULL, NULL);
+    }
+}
+
+static void nbd_update_can_read(NBDClient *client)
+{
+    bool can_read = client->recv_coroutine ||
+                    client->nb_requests < MAX_NBD_REQUESTS;
+
+    if (can_read != client->can_read) {
+        client->can_read = can_read;
+        nbd_set_handlers(client);
+
+        /* There is no need to invoke aio_notify(), since aio_set_fd_handler()
+         * in nbd_set_handlers() will have taken care of that */
+    }
+}
+
+void nbd_client_new(NBDExport *exp, int csock, void (*close_fn)(NBDClient *))
+{
+    NBDClient *client;
+    client = g_malloc0(sizeof(NBDClient));
+    client->refcount = 1;
+    client->exp = exp;
+    client->sock = csock;
+    client->can_read = true;
+    if (nbd_send_negotiate(client)) {
+        shutdown(client->sock, 2);
+        close_fn(client);
+        return;
+    }
+    client->close = close_fn;
+    qemu_co_mutex_init(&client->send_lock);
+    nbd_set_handlers(client);
+
+    if (exp) {
+        QTAILQ_INSERT_TAIL(&exp->clients, client, next);
+        nbd_export_get(exp);
+    }
+}