Merge remote-tracking branch 'bonzini/nbd-for-anthony' into staging

* bonzini/nbd-for-anthony: (26 commits)
  nbd: add myself as maintainer
  qemu-nbd: throttle requests
  qemu-nbd: asynchronous operation
  qemu-nbd: add client pointer to NBDRequest
  qemu-nbd: move client handling to nbd.c
  qemu-nbd: use common main loop
  link the main loop and its dependencies into the tools
  qemu-nbd: introduce NBDRequest
  qemu-nbd: introduce NBDExport
  qemu-nbd: introduce nbd_do_receive_request
  qemu-nbd: more robust handling of invalid requests
  qemu-nbd: introduce nbd_do_send_reply
  qemu-nbd: simplify nbd_trip
  move corking functions to osdep.c
  qemu-nbd: remove data_size argument to nbd_trip
  qemu-nbd: remove offset argument to nbd_trip
  Update ioctl order in nbd_init() to detect EBUSY
  nbd: add support for NBD_CMD_TRIM
  nbd: add support for NBD_CMD_FLUSH
  nbd: add support for NBD_CMD_FLAG_FUA
  ...

19 files changed, 1087 insertions, 530 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index e22bfa1a30..764c92dab6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -473,6 +473,13 @@ M: Mark McLoughlin <markmc@redhat.com>
 S: Maintained
 F: net/
 
+Network Block Device (NBD)
+M: Paolo Bonzini <pbonzini@redhat.com>
+S: Odd Fixes
+F: block/nbd.c
+F: nbd.*
+F: qemu-nbd.c
+
 SLIRP
 M: Jan Kiszka <jan.kiszka@siemens.com>
 S: Maintained
diff --git a/Makefile b/Makefile
index 2c030552a1..368eeae9b0 100644
--- a/Makefile
+++ b/Makefile
@@ -147,8 +147,9 @@ endif
 qemu-img.o: qemu-img-cmds.h
 qemu-img.o qemu-tool.o qemu-nbd.o qemu-io.o cmd.o qemu-ga.o: $(GENERATED_HEADERS)
 
-tools-obj-y = qemu-tool.o $(oslib-obj-y) $(trace-obj-y) \
-	qemu-timer-common.o cutils.o
+tools-obj-y = $(oslib-obj-y) $(trace-obj-y) qemu-tool.o qemu-timer.o \
+	qemu-timer-common.o main-loop.o notify.o iohandler.o cutils.o async.o
+tools-obj-$(CONFIG_POSIX) += compatfd.o
 
 qemu-img$(EXESUF): qemu-img.o $(tools-obj-y) $(block-obj-y)
 qemu-nbd$(EXESUF): qemu-nbd.o $(tools-obj-y) $(block-obj-y)
diff --git a/Makefile.objs b/Makefile.objs
index f753d838ff..8813673584 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -12,7 +12,7 @@ oslib-obj-$(CONFIG_POSIX) += oslib-posix.o qemu-thread-posix.o
 
 #######################################################################
 # coroutines
-coroutine-obj-y = qemu-coroutine.o qemu-coroutine-lock.o
+coroutine-obj-y = qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o
 ifeq ($(CONFIG_UCONTEXT_COROUTINE),y)
 coroutine-obj-$(CONFIG_POSIX) += coroutine-ucontext.o
 else
diff --git a/block/nbd.c b/block/nbd.c
index 95212dac64..161b299855 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -46,14 +46,25 @@
 #define logout(fmt, ...) ((void)0)
 #endif
 
+#define MAX_NBD_REQUESTS	16
+#define HANDLE_TO_INDEX(bs, handle) ((handle) ^ ((uint64_t)(intptr_t)bs))
+#define INDEX_TO_HANDLE(bs, index)  ((index)  ^ ((uint64_t)(intptr_t)bs))
+
 typedef struct BDRVNBDState {
-    CoMutex lock;
     int sock;
     uint32_t nbdflags;
     off_t size;
     size_t blocksize;
     char *export_name; /* An NBD server may export several devices */
 
+    CoMutex send_mutex;
+    CoMutex free_sema;
+    Coroutine *send_coroutine;
+    int in_flight;
+
+    Coroutine *recv_coroutine[MAX_NBD_REQUESTS];
+    struct nbd_reply reply;
+
     /* If it begins with  '/', this is a UNIX domain socket. Otherwise,
      * it's a string of the form <hostname|ip4|\[ip6\]>:port
      */
@@ -106,6 +117,130 @@ out:
     return err;
 }
 
+static void nbd_coroutine_start(BDRVNBDState *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 int nbd_have_request(void *opaque)
+{
+    BDRVNBDState *s = opaque;
+
+    return s->in_flight > 0;
+}
+
+static void nbd_reply_ready(void *opaque)
+{
+    BDRVNBDState *s = opaque;
+    int i;
+
+    if (s->reply.handle == 0) {
+        /* No reply already in flight.  Fetch a header.  */
+        if (nbd_receive_reply(s->sock, &s->reply) < 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 (s->recv_coroutine[i]) {
+        qemu_coroutine_enter(s->recv_coroutine[i], NULL);
+        return;
+    }
+
+fail:
+    for (i = 0; i < MAX_NBD_REQUESTS; i++) {
+        if (s->recv_coroutine[i]) {
+            qemu_coroutine_enter(s->recv_coroutine[i], NULL);
+        }
+    }
+}
+
+static void nbd_restart_write(void *opaque)
+{
+    BDRVNBDState *s = opaque;
+    qemu_coroutine_enter(s->send_coroutine, NULL);
+}
+
+static int nbd_co_send_request(BDRVNBDState *s, struct nbd_request *request,
+                               struct iovec *iov, int offset)
+{
+    int rc, ret;
+
+    qemu_co_mutex_lock(&s->send_mutex);
+    s->send_coroutine = qemu_coroutine_self();
+    qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, nbd_restart_write,
+                            nbd_have_request, NULL, s);
+    rc = nbd_send_request(s->sock, request);
+    if (rc != -1 && iov) {
+        ret = qemu_co_sendv(s->sock, iov, request->len, offset);
+        if (ret != request->len) {
+            errno = -EIO;
+            rc = -1;
+        }
+    }
+    qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, NULL,
+                            nbd_have_request, NULL, s);
+    s->send_coroutine = NULL;
+    qemu_co_mutex_unlock(&s->send_mutex);
+    return rc;
+}
+
+static void nbd_co_receive_reply(BDRVNBDState *s, struct nbd_request *request,
+                                 struct nbd_reply *reply,
+                                 struct iovec *iov, 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 (iov && reply->error == 0) {
+            ret = qemu_co_recvv(s->sock, iov, request->len, offset);
+            if (ret != request->len) {
+                reply->error = EIO;
+            }
+        }
+
+        /* Tell the read handler to read another header.  */
+        s->reply.handle = 0;
+    }
+}
+
+static void nbd_coroutine_end(BDRVNBDState *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_establish_connection(BlockDriverState *bs)
 {
     BDRVNBDState *s = bs->opaque;
@@ -135,8 +270,11 @@ static int nbd_establish_connection(BlockDriverState *bs)
         return -errno;
     }
 
-    /* Now that we're connected, set the socket to be non-blocking */
+    /* Now that we're connected, set the socket to be non-blocking and
+     * kick the reply mechanism.  */
     socket_set_nonblock(sock);
+    qemu_aio_set_fd_handler(s->sock, nbd_reply_ready, NULL,
+                            nbd_have_request, NULL, s);
 
     s->sock = sock;
     s->size = size;
@@ -152,11 +290,11 @@ static void nbd_teardown_connection(BlockDriverState *bs)
     struct nbd_request request;
 
     request.type = NBD_CMD_DISC;
-    request.handle = (uint64_t)(intptr_t)bs;
     request.from = 0;
     request.len = 0;
     nbd_send_request(s->sock, &request);
 
+    qemu_aio_set_fd_handler(s->sock, NULL, NULL, NULL, NULL, NULL);
     closesocket(s->sock);
 }
 
@@ -165,6 +303,9 @@ static int nbd_open(BlockDriverState *bs, const char* filename, int flags)
     BDRVNBDState *s = bs->opaque;
     int result;
 
+    qemu_co_mutex_init(&s->send_mutex);
+    qemu_co_mutex_init(&s->free_sema);
+
     /* Pop the config into our state object. Exit if invalid. */
     result = nbd_config(s, filename, flags);
     if (result != 0) {
@@ -176,90 +317,146 @@ static int nbd_open(BlockDriverState *bs, const char* filename, int flags)
      */
     result = nbd_establish_connection(bs);
 
-    qemu_co_mutex_init(&s->lock);
     return result;
 }
 
-static int nbd_read(BlockDriverState *bs, int64_t sector_num,
-                    uint8_t *buf, int nb_sectors)
+static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num,
+                          int nb_sectors, QEMUIOVector *qiov,
+                          int offset)
 {
     BDRVNBDState *s = bs->opaque;
     struct nbd_request request;
     struct nbd_reply reply;
 
     request.type = NBD_CMD_READ;
-    request.handle = (uint64_t)(intptr_t)bs;
     request.from = sector_num * 512;
     request.len = nb_sectors * 512;
 
-    if (nbd_send_request(s->sock, &request) == -1)
-        return -errno;
-
-    if (nbd_receive_reply(s->sock, &reply) == -1)
-        return -errno;
-
-    if (reply.error !=0)
-        return -reply.error;
-
-    if (reply.handle != request.handle)
-        return -EIO;
-
-    if (nbd_wr_sync(s->sock, buf, request.len, 1) != request.len)
-        return -EIO;
+    nbd_coroutine_start(s, &request);
+    if (nbd_co_send_request(s, &request, NULL, 0) == -1) {
+        reply.error = errno;
+    } else {
+        nbd_co_receive_reply(s, &request, &reply, qiov->iov, offset);
+    }
+    nbd_coroutine_end(s, &request);
+    return -reply.error;
 
-    return 0;
 }
 
-static int nbd_write(BlockDriverState *bs, int64_t sector_num,
-                     const uint8_t *buf, int nb_sectors)
+static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,
+                           int nb_sectors, QEMUIOVector *qiov,
+                           int offset)
 {
     BDRVNBDState *s = bs->opaque;
     struct nbd_request request;
     struct nbd_reply reply;
 
     request.type = NBD_CMD_WRITE;
-    request.handle = (uint64_t)(intptr_t)bs;
+    if (!bdrv_enable_write_cache(bs) && (s->nbdflags & NBD_FLAG_SEND_FUA)) {
+        request.type |= NBD_CMD_FLAG_FUA;
+    }
+
     request.from = sector_num * 512;
     request.len = nb_sectors * 512;
 
-    if (nbd_send_request(s->sock, &request) == -1)
-        return -errno;
-
-    if (nbd_wr_sync(s->sock, (uint8_t*)buf, request.len, 0) != request.len)
-        return -EIO;
-
-    if (nbd_receive_reply(s->sock, &reply) == -1)
-        return -errno;
-
-    if (reply.error !=0)
-        return -reply.error;
+    nbd_coroutine_start(s, &request);
+    if (nbd_co_send_request(s, &request, qiov->iov, offset) == -1) {
+        reply.error = errno;
+    } else {
+        nbd_co_receive_reply(s, &request, &reply, NULL, 0);
+    }
+    nbd_coroutine_end(s, &request);
+    return -reply.error;
+}
 
-    if (reply.handle != request.handle)
-        return -EIO;
+/* qemu-nbd has a limit of slightly less than 1M per request.  Try to
+ * remain aligned to 4K. */
+#define NBD_MAX_SECTORS 2040
 
-    return 0;
+static int nbd_co_readv(BlockDriverState *bs, 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(bs, 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(bs, sector_num, nb_sectors, qiov, offset);
 }
 
-static coroutine_fn int nbd_co_read(BlockDriverState *bs, int64_t sector_num,
-                                    uint8_t *buf, int nb_sectors)
+static int nbd_co_writev(BlockDriverState *bs, 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(bs, 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(bs, sector_num, nb_sectors, qiov, offset);
+}
+
+static int nbd_co_flush(BlockDriverState *bs)
+{
     BDRVNBDState *s = bs->opaque;
-    qemu_co_mutex_lock(&s->lock);
-    ret = nbd_read(bs, sector_num, buf, nb_sectors);
-    qemu_co_mutex_unlock(&s->lock);
-    return ret;
+    struct nbd_request request;
+    struct nbd_reply reply;
+
+    if (!(s->nbdflags & NBD_FLAG_SEND_FLUSH)) {
+        return 0;
+    }
+
+    request.type = NBD_CMD_FLUSH;
+    if (s->nbdflags & NBD_FLAG_SEND_FUA) {
+        request.type |= NBD_CMD_FLAG_FUA;
+    }
+
+    request.from = 0;
+    request.len = 0;
+
+    nbd_coroutine_start(s, &request);
+    if (nbd_co_send_request(s, &request, NULL, 0) == -1) {
+        reply.error = errno;
+    } else {
+        nbd_co_receive_reply(s, &request, &reply, NULL, 0);
+    }
+    nbd_coroutine_end(s, &request);
+    return -reply.error;
 }
 
-static coroutine_fn int nbd_co_write(BlockDriverState *bs, int64_t sector_num,
-                                     const uint8_t *buf, int nb_sectors)
+static int nbd_co_discard(BlockDriverState *bs, int64_t sector_num,
+                          int nb_sectors)
 {
-    int ret;
     BDRVNBDState *s = bs->opaque;
-    qemu_co_mutex_lock(&s->lock);
-    ret = nbd_write(bs, sector_num, buf, nb_sectors);
-    qemu_co_mutex_unlock(&s->lock);
-    return ret;
+    struct nbd_request request;
+    struct nbd_reply reply;
+
+    if (!(s->nbdflags & NBD_FLAG_SEND_TRIM)) {
+        return 0;
+    }
+    request.type = NBD_CMD_TRIM;
+    request.from = sector_num * 512;;
+    request.len = nb_sectors * 512;
+
+    nbd_coroutine_start(s, &request);
+    if (nbd_co_send_request(s, &request, NULL, 0) == -1) {
+        reply.error = errno;
+    } else {
+        nbd_co_receive_reply(s, &request, &reply, NULL, 0);
+    }
+    nbd_coroutine_end(s, &request);
+    return -reply.error;
 }
 
 static void nbd_close(BlockDriverState *bs)
@@ -279,14 +476,16 @@ static int64_t nbd_getlength(BlockDriverState *bs)
 }
 
 static BlockDriver bdrv_nbd = {
-    .format_name	= "nbd",
-    .instance_size	= sizeof(BDRVNBDState),
-    .bdrv_file_open	= nbd_open,
-    .bdrv_read          = nbd_co_read,
-    .bdrv_write         = nbd_co_write,
-    .bdrv_close		= nbd_close,
-    .bdrv_getlength	= nbd_getlength,
-    .protocol_name	= "nbd",
+    .format_name         = "nbd",
+    .instance_size       = sizeof(BDRVNBDState),
+    .bdrv_file_open      = nbd_open,
+    .bdrv_co_readv       = nbd_co_readv,
+    .bdrv_co_writev      = nbd_co_writev,
+    .bdrv_close          = nbd_close,
+    .bdrv_co_flush_to_os = nbd_co_flush,
+    .bdrv_co_discard     = nbd_co_discard,
+    .bdrv_getlength      = nbd_getlength,
+    .protocol_name       = "nbd",
 };
 
 static void bdrv_nbd_init(void)
diff --git a/block/sheepdog.c b/block/sheepdog.c
index aa9707f2ae..17a79beb24 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -443,129 +443,6 @@ static SheepdogAIOCB *sd_aio_setup(BlockDriverState *bs, QEMUIOVector *qiov,
     return acb;
 }
 
-#ifdef _WIN32
-
-struct msghdr {
-    struct iovec *msg_iov;
-    size_t        msg_iovlen;
-};
-
-static ssize_t sendmsg(int s, const struct msghdr *msg, int flags)
-{
-    size_t size = 0;
-    char *buf, *p;
-    int i, ret;
-
-    /* count the msg size */
-    for (i = 0; i < msg->msg_iovlen; i++) {
-        size += msg->msg_iov[i].iov_len;
-    }
-    buf = g_malloc(size);
-
-    p = buf;
-    for (i = 0; i < msg->msg_iovlen; i++) {
-        memcpy(p, msg->msg_iov[i].iov_base, msg->msg_iov[i].iov_len);
-        p += msg->msg_iov[i].iov_len;
-    }
-
-    ret = send(s, buf, size, flags);
-
-    g_free(buf);
-    return ret;
-}
-
-static ssize_t recvmsg(int s, struct msghdr *msg, int flags)
-{
-    size_t size = 0;
-    char *buf, *p;
-    int i, ret;
-
-    /* count the msg size */
-    for (i = 0; i < msg->msg_iovlen; i++) {
-        size += msg->msg_iov[i].iov_len;
-    }
-    buf = g_malloc(size);
-
-    ret = qemu_recv(s, buf, size, flags);
-    if (ret < 0) {
-        goto out;
-    }
-
-    p = buf;
-    for (i = 0; i < msg->msg_iovlen; i++) {
-        memcpy(msg->msg_iov[i].iov_base, p, msg->msg_iov[i].iov_len);
-        p += msg->msg_iov[i].iov_len;
-    }
-out:
-    g_free(buf);
-    return ret;
-}
-
-#endif
-
-/*
- * Send/recv data with iovec buffers
- *
- * This function send/recv data from/to the iovec buffer directly.
- * The first `offset' bytes in the iovec buffer are skipped and next
- * `len' bytes are used.
- *
- * For example,
- *
- *   do_send_recv(sockfd, iov, len, offset, 1);
- *
- * is equals to
- *
- *   char *buf = malloc(size);
- *   iov_to_buf(iov, iovcnt, buf, offset, size);
- *   send(sockfd, buf, size, 0);
- *   free(buf);
- */
-static int do_send_recv(int sockfd, struct iovec *iov, int len, int offset,
-                        int write)
-{
-    struct msghdr msg;
-    int ret, diff;
-
-    memset(&msg, 0, sizeof(msg));
-    msg.msg_iov = iov;
-    msg.msg_iovlen = 1;
-
-    len += offset;
-
-    while (iov->iov_len < len) {
-        len -= iov->iov_len;
-
-        iov++;
-        msg.msg_iovlen++;
-    }
-
-    diff = iov->iov_len - len;
-    iov->iov_len -= diff;
-
-    while (msg.msg_iov->iov_len <= offset) {
-        offset -= msg.msg_iov->iov_len;
-
-        msg.msg_iov++;
-        msg.msg_iovlen--;
-    }
-
-    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base + offset;
-    msg.msg_iov->iov_len -= offset;
-
-    if (write) {
-        ret = sendmsg(sockfd, &msg, 0);
-    } else {
-        ret = recvmsg(sockfd, &msg, 0);
-    }
-
-    msg.msg_iov->iov_base = (char *) msg.msg_iov->iov_base - offset;
-    msg.msg_iov->iov_len += offset;
-
-    iov->iov_len += diff;
-    return ret;
-}
-
 static int connect_to_sdog(const char *addr, const char *port)
 {
     char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
@@ -618,83 +495,19 @@ success:
     return fd;
 }
 
-static int do_readv_writev(int sockfd, struct iovec *iov, int len,
-                           int iov_offset, int write)
-{
-    int ret;
-again:
-    ret = do_send_recv(sockfd, iov, len, iov_offset, write);
-    if (ret < 0) {
-        if (errno == EINTR) {
-            goto again;
-        }
-        if (errno == EAGAIN) {
-            if (qemu_in_coroutine()) {
-                qemu_coroutine_yield();
-            }
-            goto again;
-        }
-        error_report("failed to recv a rsp, %s", strerror(errno));
-        return 1;
-    }
-
-    iov_offset += ret;
-    len -= ret;
-    if (len) {
-        goto again;
-    }
-
-    return 0;
-}
-
-static int do_readv(int sockfd, struct iovec *iov, int len, int iov_offset)
-{
-    return do_readv_writev(sockfd, iov, len, iov_offset, 0);
-}
-
-static int do_writev(int sockfd, struct iovec *iov, int len, int iov_offset)
-{
-    return do_readv_writev(sockfd, iov, len, iov_offset, 1);
-}
-
-static int do_read_write(int sockfd, void *buf, int len, int write)
-{
-    struct iovec iov;
-
-    iov.iov_base = buf;
-    iov.iov_len = len;
-
-    return do_readv_writev(sockfd, &iov, len, 0, write);
-}
-
-static int do_read(int sockfd, void *buf, int len)
-{
-    return do_read_write(sockfd, buf, len, 0);
-}
-
-static int do_write(int sockfd, void *buf, int len)
-{
-    return do_read_write(sockfd, buf, len, 1);
-}
-
 static int send_req(int sockfd, SheepdogReq *hdr, void *data,
                     unsigned int *wlen)
 {
     int ret;
-    struct iovec iov[2];
 
-    iov[0].iov_base = hdr;
-    iov[0].iov_len = sizeof(*hdr);
-
-    if (*wlen) {
-        iov[1].iov_base = data;
-        iov[1].iov_len = *wlen;
+    ret = qemu_send_full(sockfd, hdr, sizeof(*hdr), 0);
+    if (ret < sizeof(*hdr)) {
+        error_report("failed to send a req, %s", strerror(errno));
     }
 
-    ret = do_writev(sockfd, iov, sizeof(*hdr) + *wlen, 0);
-    if (ret) {
+    ret = qemu_send_full(sockfd, data, *wlen, 0);
+    if (ret < *wlen) {
         error_report("failed to send a req, %s", strerror(errno));
-        ret = -1;
     }
 
     return ret;
@@ -705,16 +518,15 @@ static int do_req(int sockfd, SheepdogReq *hdr, void *data,
 {
     int ret;
 
+    socket_set_block(sockfd);
     ret = send_req(sockfd, hdr, data, wlen);
-    if (ret) {
-        ret = -1;
+    if (ret < 0) {
         goto out;
     }
 
-    ret = do_read(sockfd, hdr, sizeof(*hdr));
-    if (ret) {
+    ret = qemu_recv_full(sockfd, hdr, sizeof(*hdr), 0);
+    if (ret < sizeof(*hdr)) {
         error_report("failed to get a rsp, %s", strerror(errno));
-        ret = -1;
         goto out;
     }
 
@@ -723,15 +535,15 @@ static int do_req(int sockfd, SheepdogReq *hdr, void *data,
     }
 
     if (*rlen) {
-        ret = do_read(sockfd, data, *rlen);
-        if (ret) {
+        ret = qemu_recv_full(sockfd, data, *rlen, 0);
+        if (ret < *rlen) {
             error_report("failed to get the data, %s", strerror(errno));
-            ret = -1;
             goto out;
         }
     }
     ret = 0;
 out:
+    socket_set_nonblock(sockfd);
     return ret;
 }
 
@@ -793,8 +605,8 @@ static void coroutine_fn aio_read_response(void *opaque)
     }
 
     /* read a header */
-    ret = do_read(fd, &rsp, sizeof(rsp));
-    if (ret) {
+    ret = qemu_co_recv(fd, &rsp, sizeof(rsp));
+    if (ret < 0) {
         error_report("failed to get the header, %s", strerror(errno));
         goto out;
     }
@@ -839,9 +651,9 @@ static void coroutine_fn aio_read_response(void *opaque)
         }
         break;
     case AIOCB_READ_UDATA:
-        ret = do_readv(fd, acb->qiov->iov, rsp.data_length,
-                       aio_req->iov_offset);
-        if (ret) {
+        ret = qemu_co_recvv(fd, acb->qiov->iov, rsp.data_length,
+                            aio_req->iov_offset);
+        if (ret < 0) {
             error_report("failed to get the data, %s", strerror(errno));
             goto out;
         }
@@ -890,22 +702,6 @@ static int aio_flush_request(void *opaque)
     return !QLIST_EMPTY(&s->outstanding_aio_head);
 }
 
-#if !defined(SOL_TCP) || !defined(TCP_CORK)
-
-static int set_cork(int fd, int v)
-{
-    return 0;
-}
-
-#else
-
-static int set_cork(int fd, int v)
-{
-    return setsockopt(fd, SOL_TCP, TCP_CORK, &v, sizeof(v));
-}
-
-#endif
-
 static int set_nodelay(int fd)
 {
     int ret, opt;
@@ -1111,26 +907,26 @@ static int coroutine_fn add_aio_request(BDRVSheepdogState *s, AIOReq *aio_req,
     s->co_send = qemu_coroutine_self();
     qemu_aio_set_fd_handler(s->fd, co_read_response, co_write_request,
                             aio_flush_request, NULL, s);
-    set_cork(s->fd, 1);
+    socket_set_cork(s->fd, 1);
 
     /* send a header */
-    ret = do_write(s->fd, &hdr, sizeof(hdr));
-    if (ret) {
+    ret = qemu_co_send(s->fd, &hdr, sizeof(hdr));
+    if (ret < 0) {
         qemu_co_mutex_unlock(&s->lock);
         error_report("failed to send a req, %s", strerror(errno));
         return -EIO;
     }
 
     if (wlen) {
-        ret = do_writev(s->fd, iov, wlen, aio_req->iov_offset);
-        if (ret) {
+        ret = qemu_co_sendv(s->fd, iov, wlen, aio_req->iov_offset);
+        if (ret < 0) {
             qemu_co_mutex_unlock(&s->lock);
             error_report("failed to send a data, %s", strerror(errno));
             return -EIO;
         }
     }
 
-    set_cork(s->fd, 0);
+    socket_set_cork(s->fd, 0);
     qemu_aio_set_fd_handler(s->fd, co_read_response, NULL,
                             aio_flush_request, NULL, s);
     qemu_co_mutex_unlock(&s->lock);
diff --git a/cutils.c b/cutils.c
index 24b3fe355b..a6ffd46445 100644
--- a/cutils.c
+++ b/cutils.c
@@ -25,6 +25,8 @@
 #include "host-utils.h"
 #include <math.h>
 
+#include "qemu_socket.h"
+
 void pstrcpy(char *buf, int buf_size, const char *str)
 {
     int c;
@@ -403,3 +405,112 @@ int qemu_parse_fd(const char *param)
     }
     return fd;
 }
+
+/*
+ * Send/recv data with iovec buffers
+ *
+ * This function send/recv data from/to the iovec buffer directly.
+ * The first `offset' bytes in the iovec buffer are skipped and next
+ * `len' bytes are used.
+ *
+ * For example,
+ *
+ *   do_sendv_recvv(sockfd, iov, len, offset, 1);
+ *
+ * is equal to
+ *
+ *   char *buf = malloc(size);
+ *   iov_to_buf(iov, iovcnt, buf, offset, size);
+ *   send(sockfd, buf, size, 0);
+ *   free(buf);
+ */
+static int do_sendv_recvv(int sockfd, struct iovec *iov, int len, int offset,
+                          int do_sendv)
+{
+    int ret, diff, iovlen;
+    struct iovec *last_iov;
+
+    /* last_iov is inclusive, so count from one.  */
+    iovlen = 1;
+    last_iov = iov;
+    len += offset;
+
+    while (last_iov->iov_len < len) {
+        len -= last_iov->iov_len;
+
+        last_iov++;
+        iovlen++;
+    }
+
+    diff = last_iov->iov_len - len;
+    last_iov->iov_len -= diff;
+
+    while (iov->iov_len <= offset) {
+        offset -= iov->iov_len;
+
+        iov++;
+        iovlen--;
+    }
+
+    iov->iov_base = (char *) iov->iov_base + offset;
+    iov->iov_len -= offset;
+
+    {
+#if defined CONFIG_IOVEC && defined CONFIG_POSIX
+        struct msghdr msg;
+        memset(&msg, 0, sizeof(msg));
+        msg.msg_iov = iov;
+        msg.msg_iovlen = iovlen;
+
+        do {
+            if (do_sendv) {
+                ret = sendmsg(sockfd, &msg, 0);
+            } else {
+                ret = recvmsg(sockfd, &msg, 0);
+            }
+        } while (ret == -1 && errno == EINTR);
+#else
+        struct iovec *p = iov;
+        ret = 0;
+        while (iovlen > 0) {
+            int rc;
+            if (do_sendv) {
+                rc = send(sockfd, p->iov_base, p->iov_len, 0);
+            } else {
+                rc = qemu_recv(sockfd, p->iov_base, p->iov_len, 0);
+            }
+            if (rc == -1) {
+                if (errno == EINTR) {
+                    continue;
+                }
+                if (ret == 0) {
+                    ret = -1;
+                }
+                break;
+            }
+            if (rc == 0) {
+                break;
+            }
+            ret += rc;
+            iovlen--, p++;
+        }
+#endif
+    }
+
+    /* Undo the changes above */
+    iov->iov_base = (char *) iov->iov_base - offset;
+    iov->iov_len += offset;
+    last_iov->iov_len += diff;
+    return ret;
+}
+
+int qemu_recvv(int sockfd, struct iovec *iov, int len, int iov_offset)
+{
+    return do_sendv_recvv(sockfd, iov, len, iov_offset, 0);
+}
+
+int qemu_sendv(int sockfd, struct iovec *iov, int len, int iov_offset)
+{
+    return do_sendv_recvv(sockfd, iov, len, iov_offset, 1);
+}
+
diff --git a/main-loop.h b/main-loop.h
index 876092dd15..f9710136c9 100644
--- a/main-loop.h
+++ b/main-loop.h
@@ -324,6 +324,9 @@ int qemu_add_child_watch(pid_t pid);
  * by threads other than the main loop thread when calling
  * qemu_bh_new(), qemu_set_fd_handler() and basically all other
  * functions documented in this file.
+ *
+ * NOTE: tools currently are single-threaded and qemu_mutex_lock_iothread
+ * is a no-op there.
  */
 void qemu_mutex_lock_iothread(void);
 
@@ -336,6 +339,9 @@ void qemu_mutex_lock_iothread(void);
  * as soon as possible by threads other than the main loop thread,
  * because it prevents the main loop from processing callbacks,
  * including timers and bottom halves.
+ *
+ * NOTE: tools currently are single-threaded and qemu_mutex_unlock_iothread
+ * is a no-op there.
  */
 void qemu_mutex_unlock_iothread(void);
 
diff --git a/nbd.c b/nbd.c
index de880fe3c6..567e94e27a 100644
--- a/nbd.c
+++ b/nbd.c
@@ -18,6 +18,9 @@
 
 #include "nbd.h"
 #include "block.h"
+#include "block_int.h"
+
+#include "qemu-coroutine.h"
 
 #include <errno.h>
 #include <string.h>
@@ -35,6 +38,7 @@
 #endif
 
 #include "qemu_socket.h"
+#include "qemu-queue.h"
 
 //#define DEBUG_NBD
 
@@ -81,6 +85,14 @@ 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;
 
@@ -178,7 +190,7 @@ int unix_socket_outgoing(const char *path)
                   Request (type == 2)
 */
 
-int nbd_negotiate(int csock, off_t size, uint32_t flags)
+static int nbd_send_negotiate(int csock, off_t size, uint32_t flags)
 {
     char buf[8 + 8 + 8 + 128];
 
@@ -194,7 +206,9 @@ int nbd_negotiate(int csock, off_t size, uint32_t flags)
     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);
+    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)) {
@@ -348,6 +362,15 @@ int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
 #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) {
@@ -386,24 +409,6 @@ int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize)
         return -1;
     }
 
-    TRACE("Clearing NBD socket");
-
-    if (ioctl(fd, NBD_CLEAR_SOCK) == -1) {
-        int serrno = errno;
-        LOG("Failed clearing NBD socket");
-        errno = serrno;
-        return -1;
-    }
-
-    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("Negotiation ended");
 
     return 0;
@@ -582,121 +587,369 @@ static int nbd_send_reply(int csock, struct nbd_reply *reply)
     return 0;
 }
 
-int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
-             off_t *offset, uint32_t nbdflags, uint8_t *data, int data_size)
+#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)
 {
-    struct nbd_request request;
-    struct nbd_reply reply;
+    client->refcount++;
+}
 
-    TRACE("Reading request.");
+static void nbd_client_put(NBDClient *client)
+{
+    if (--client->refcount == 0) {
+        g_free(client);
+    }
+}
 
-    if (nbd_receive_request(csock, &request) == -1)
-        return -1;
+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;
 
-    if (request.len + NBD_REPLY_SIZE > data_size) {
+    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_REPLY_SIZE, data_size);
-        errno = EINVAL;
-        return -1;
+            request->len, NBD_BUFFER_SIZE);
+        rc = -EINVAL;
+        goto out;
     }
 
-    if ((request.from + request.len) < request.from) {
+    if ((request->from + request->len) < request->from) {
         LOG("integer overflow detected! "
             "you're probably being attacked");
-        errno = EINVAL;
-        return -1;
+        rc = -EINVAL;
+        goto out;
     }
 
-    if ((request.from + request.len) > size) {
-            LOG("From: %" PRIu64 ", Len: %u, Size: %" PRIu64
-            ", Offset: %" PRIu64 "\n",
-                    request.from, request.len, (uint64_t)size, dev_offset);
-        LOG("requested operation past EOF--bad client?");
-        errno = EINVAL;
-        return -1;
+    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;
 
-    TRACE("Decoding type");
+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;
 
-    switch (request.type) {
+    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");
 
-        if (bdrv_read(bs, (request.from + dev_offset) / 512,
-                  data + NBD_REPLY_SIZE,
-                  request.len / 512) == -1) {
+        ret = bdrv_read(exp->bs, (request.from + exp->dev_offset) / 512,
+                        req->data, request.len / 512);
+        if (ret < 0) {
             LOG("reading from file failed");
-            errno = EINVAL;
-            return -1;
+            reply.error = -ret;
+            goto error_reply;
         }
-        *offset += request.len;
 
         TRACE("Read %u byte(s)", request.len);
-
-        /* Reply
-           [ 0 ..  3]    magic   (NBD_REPLY_MAGIC)
-           [ 4 ..  7]    error   (0 == no error)
-           [ 7 .. 15]    handle
-         */
-
-        cpu_to_be32w((uint32_t*)data, NBD_REPLY_MAGIC);
-        cpu_to_be32w((uint32_t*)(data + 4), reply.error);
-        cpu_to_be64w((uint64_t*)(data + 8), reply.handle);
-
-        TRACE("Sending data to client");
-
-        if (write_sync(csock, data,
-                   request.len + NBD_REPLY_SIZE) !=
-                   request.len + NBD_REPLY_SIZE) {
-            LOG("writing to socket failed");
-            errno = EINVAL;
-            return -1;
-        }
+        if (nbd_co_send_reply(req, &reply, request.len) < 0)
+            goto out;
         break;
     case NBD_CMD_WRITE:
         TRACE("Request type is WRITE");
 
-        TRACE("Reading %u byte(s)", request.len);
-
-        if (read_sync(csock, data, request.len) != request.len) {
-            LOG("reading from socket failed");
-            errno = EINVAL;
-            return -1;
+        if (exp->nbdflags & NBD_FLAG_READ_ONLY) {
+            TRACE("Server is read-only, return error");
+            reply.error = EROFS;
+            goto error_reply;
         }
 
-        if (nbdflags & NBD_FLAG_READ_ONLY) {
-            TRACE("Server is read-only, return error");
-            reply.error = 1;
-        } else {
-            TRACE("Writing to device");
+        TRACE("Writing to device");
 
-            if (bdrv_write(bs, (request.from + dev_offset) / 512,
-                       data, request.len / 512) == -1) {
-                LOG("writing to file failed");
-                errno = EINVAL;
-                return -1;
-            }
+        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;
+        }
 
-            *offset += request.len;
+        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_send_reply(csock, &reply) == -1)
-            return -1;
+        if (nbd_co_send_reply(req, &reply, 0) < 0)
+            goto out;
         break;
     case NBD_CMD_DISC:
         TRACE("Request type is DISCONNECT");
         errno = 0;
-        return 1;
+        goto out;
+    case NBD_CMD_FLUSH:
+        TRACE("Request type is FLUSH");
+
+        ret = bdrv_co_flush(exp->bs);
+        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 = bdrv_co_discard(exp->bs, (request.from + exp->dev_offset) / 512,
+                              request.len / 512);
+        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);
-        errno = EINVAL;
-        return -1;
+    invalid_request:
+        reply.error = -EINVAL;
+    error_reply:
+        if (nbd_co_send_reply(req, &reply, 0) == -1)
+            goto out;
+        break;
     }
 
     TRACE("Request/Reply complete");
 
-    return 0;
+    nbd_request_put(req);
+    return;
+
+out:
+    nbd_request_put(req);
+    nbd_client_close(client);
+}
+
+static int nbd_can_read(void *opaque)
+{
+    NBDClient *client = opaque;
+
+    return client->recv_coroutine || client->nb_requests < MAX_NBD_REQUESTS;
+}
+
+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);
+}
+
+NBDClient *nbd_client_new(NBDExport *exp, int csock,
+                          void (*close)(NBDClient *))
+{
+    NBDClient *client;
+    if (nbd_send_negotiate(csock, exp->size, exp->nbdflags) == -1) {
+        return NULL;
+    }
+    client = g_malloc0(sizeof(NBDClient));
+    client->refcount = 1;
+    client->exp = exp;
+    client->sock = csock;
+    client->close = close;
+    qemu_co_mutex_init(&client->send_lock);
+    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read, NULL, client);
+    return client;
 }
diff --git a/nbd.h b/nbd.h
index 61553f4128..a8382f096c 100644
--- a/nbd.h
+++ b/nbd.h
@@ -57,6 +57,8 @@ enum {
 
 #define NBD_DEFAULT_PORT	10809
 
+#define NBD_BUFFER_SIZE (1024*1024)
+
 size_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read);
 int tcp_socket_outgoing(const char *address, uint16_t port);
 int tcp_socket_incoming(const char *address, uint16_t port);
@@ -65,15 +67,21 @@ int tcp_socket_incoming_spec(const char *address_and_port);
 int unix_socket_outgoing(const char *path);
 int unix_socket_incoming(const char *path);
 
-int nbd_negotiate(int csock, off_t size, uint32_t flags);
 int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
                           off_t *size, size_t *blocksize);
 int nbd_init(int fd, int csock, uint32_t flags, off_t size, size_t blocksize);
 int nbd_send_request(int csock, struct nbd_request *request);
 int nbd_receive_reply(int csock, struct nbd_reply *reply);
-int nbd_trip(BlockDriverState *bs, int csock, off_t size, uint64_t dev_offset,
-             off_t *offset, uint32_t nbdflags, uint8_t *data, int data_size);
 int nbd_client(int fd);
 int nbd_disconnect(int fd);
 
+typedef struct NBDExport NBDExport;
+typedef struct NBDClient NBDClient;
+
+NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,
+                          off_t size, uint32_t nbdflags);
+void nbd_export_close(NBDExport *exp);
+NBDClient *nbd_client_new(NBDExport *exp, int csock,
+                          void (*close)(NBDClient *));
+
 #endif
diff --git a/os-posix.c b/os-posix.c
index dc4a6bb3ff..5c437ca12c 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -42,11 +42,6 @@
 
 #ifdef CONFIG_LINUX
 #include <sys/prctl.h>
-#include <sys/syscall.h>
-#endif
-
-#ifdef CONFIG_EVENTFD
-#include <sys/eventfd.h>
 #endif
 
 static struct passwd *user_pwd;
@@ -333,34 +328,6 @@ void os_set_line_buffering(void)
     setvbuf(stdout, NULL, _IOLBF, 0);
 }
 
-/*
- * Creates an eventfd that looks like a pipe and has EFD_CLOEXEC set.
- */
-int qemu_eventfd(int fds[2])
-{
-#ifdef CONFIG_EVENTFD
-    int ret;
-
-    ret = eventfd(0, 0);
-    if (ret >= 0) {
-        fds[0] = ret;
-        qemu_set_cloexec(ret);
-        if ((fds[1] = dup(ret)) == -1) {
-            close(ret);
-            return -1;
-        }
-        qemu_set_cloexec(fds[1]);
-        return 0;
-    }
-
-    if (errno != ENOSYS) {
-        return -1;
-    }
-#endif
-
-    return qemu_pipe(fds);
-}
-
 int qemu_create_pidfile(const char *filename)
 {
     char buffer[128];
@@ -384,12 +351,3 @@ int qemu_create_pidfile(const char *filename)
     close(fd);
     return 0;
 }
-
-int qemu_get_thread_id(void)
-{
-#if defined (__linux__)
-    return syscall(SYS_gettid);
-#else
-    return getpid();
-#endif
-}
diff --git a/os-win32.c b/os-win32.c
index 8523d8d0c4..ad76370c7c 100644
--- a/os-win32.c
+++ b/os-win32.c
@@ -151,8 +151,3 @@ int qemu_create_pidfile(const char *filename)
     }
     return 0;
 }
-
-int qemu_get_thread_id(void)
-{
-    return GetCurrentThreadId();
-}
diff --git a/osdep.c b/osdep.c
index 56e6963f15..3e6badac1e 100644
--- a/osdep.c
+++ b/osdep.c
@@ -48,6 +48,15 @@ extern int madvise(caddr_t, size_t, int);
 #include "trace.h"
 #include "qemu_socket.h"
 
+int socket_set_cork(int fd, int v)
+{
+#if defined(SOL_TCP) && defined(TCP_CORK)
+    return setsockopt(fd, SOL_TCP, TCP_CORK, &v, sizeof(v));
+#else
+    return 0;
+#endif
+}
+
 int qemu_madvise(void *addr, size_t len, int advice)
 {
     if (advice == QEMU_MADV_INVALID) {
@@ -166,3 +175,70 @@ int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen)
 
     return ret;
 }
+
+/*
+ * A variant of send(2) which handles partial write.
+ *
+ * Return the number of bytes transferred, which is only
+ * smaller than `count' if there is an error.
+ *
+ * This function won't work with non-blocking fd's.
+ * Any of the possibilities with non-bloking fd's is bad:
+ *   - return a short write (then name is wrong)
+ *   - busy wait adding (errno == EAGAIN) to the loop
+ */
+ssize_t qemu_send_full(int fd, const void *buf, size_t count, int flags)
+{
+    ssize_t ret = 0;
+    ssize_t total = 0;
+
+    while (count) {
+        ret = send(fd, buf, count, flags);
+        if (ret < 0) {
+            if (errno == EINTR) {
+                continue;
+            }
+            break;
+        }
+
+        count -= ret;
+        buf += ret;
+        total += ret;
+    }
+
+    return total;
+}
+
+/*
+ * A variant of recv(2) which handles partial write.
+ *
+ * Return the number of bytes transferred, which is only
+ * smaller than `count' if there is an error.
+ *
+ * This function won't work with non-blocking fd's.
+ * Any of the possibilities with non-bloking fd's is bad:
+ *   - return a short write (then name is wrong)
+ *   - busy wait adding (errno == EAGAIN) to the loop
+ */
+ssize_t qemu_recv_full(int fd, void *buf, size_t count, int flags)
+{
+    ssize_t ret = 0;
+    ssize_t total = 0;
+
+    while (count) {
+        ret = qemu_recv(fd, buf, count, flags);
+        if (ret <= 0) {
+            if (ret < 0 && errno == EINTR) {
+                continue;
+            }
+            break;
+        }
+
+        count -= ret;
+        buf += ret;
+        total += ret;
+    }
+
+    return total;
+}
+
diff --git a/oslib-posix.c b/oslib-posix.c
index ce755496b5..b6a3c7fc55 100644
--- a/oslib-posix.c
+++ b/oslib-posix.c
@@ -55,6 +55,21 @@ static int running_on_valgrind = -1;
 #else
 #  define running_on_valgrind 0
 #endif
+#ifdef CONFIG_LINUX
+#include <sys/syscall.h>
+#endif
+#ifdef CONFIG_EVENTFD
+#include <sys/eventfd.h>
+#endif
+
+int qemu_get_thread_id(void)
+{
+#if defined(__linux__)
+    return syscall(SYS_gettid);
+#else
+    return getpid();
+#endif
+}
 
 int qemu_daemon(int nochdir, int noclose)
 {
@@ -162,6 +177,34 @@ int qemu_pipe(int pipefd[2])
     return ret;
 }
 
+/*
+ * Creates an eventfd that looks like a pipe and has EFD_CLOEXEC set.
+ */
+int qemu_eventfd(int fds[2])
+{
+#ifdef CONFIG_EVENTFD
+    int ret;
+
+    ret = eventfd(0, 0);
+    if (ret >= 0) {
+        fds[0] = ret;
+        fds[1] = dup(ret);
+        if (fds[1] == -1) {
+            close(ret);
+            return -1;
+        }
+        qemu_set_cloexec(ret);
+        qemu_set_cloexec(fds[1]);
+        return 0;
+    }
+    if (errno != ENOSYS) {
+        return -1;
+    }
+#endif
+
+    return qemu_pipe(fds);
+}
+
 int qemu_utimens(const char *path, const struct timespec *times)
 {
     struct timeval tv[2], tv_now;
diff --git a/oslib-win32.c b/oslib-win32.c
index 5e3de7dc8a..ce3021e6c7 100644
--- a/oslib-win32.c
+++ b/oslib-win32.c
@@ -118,3 +118,8 @@ int qemu_gettimeofday(qemu_timeval *tp)
      Do not set errno on error.  */
   return 0;
 }
+
+int qemu_get_thread_id(void)
+{
+    return GetCurrentThreadId();
+}
diff --git a/qemu-common.h b/qemu-common.h
index b2de015629..6ab7dfb1b9 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -173,6 +173,10 @@ void *qemu_oom_check(void *ptr);
 int qemu_open(const char *name, int flags, ...);
 ssize_t qemu_write_full(int fd, const void *buf, size_t count)
     QEMU_WARN_UNUSED_RESULT;
+ssize_t qemu_send_full(int fd, const void *buf, size_t count, int flags)
+    QEMU_WARN_UNUSED_RESULT;
+ssize_t qemu_recv_full(int fd, void *buf, size_t count, int flags)
+    QEMU_WARN_UNUSED_RESULT;
 void qemu_set_cloexec(int fd);
 
 #ifndef _WIN32
@@ -186,6 +190,9 @@ int qemu_pipe(int pipefd[2]);
 #define qemu_recv(sockfd, buf, len, flags) recv(sockfd, buf, len, flags)
 #endif
 
+int qemu_recvv(int sockfd, struct iovec *iov, int len, int iov_offset);
+int qemu_sendv(int sockfd, struct iovec *iov, int len, int iov_offset);
+
 /* Error handling.  */
 
 void QEMU_NORETURN hw_error(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
@@ -272,6 +279,33 @@ struct qemu_work_item {
 void qemu_init_vcpu(void *env);
 #endif
 
+/**
+ * Sends an iovec (or optionally a part of it) down a socket, yielding
+ * when the socket is full.
+ */
+int qemu_co_sendv(int sockfd, struct iovec *iov,
+                  int len, int iov_offset);
+
+/**
+ * Receives data into an iovec (or optionally into a part of it) from
+ * a socket, yielding when there is no data in the socket.
+ */
+int qemu_co_recvv(int sockfd, struct iovec *iov,
+                  int len, int iov_offset);
+
+
+/**
+ * Sends a buffer down a socket, yielding when the socket is full.
+ */
+int qemu_co_send(int sockfd, void *buf, int len);
+
+/**
+ * Receives data into a buffer from a socket, yielding when there
+ * is no data in the socket.
+ */
+int qemu_co_recv(int sockfd, void *buf, int len);
+
+
 typedef struct QEMUIOVector {
     struct iovec *iov;
     int niov;
diff --git a/qemu-coroutine-io.c b/qemu-coroutine-io.c
new file mode 100644
index 0000000000..40fd514395
--- /dev/null
+++ b/qemu-coroutine-io.c
@@ -0,0 +1,96 @@
+/*
+ * Coroutine-aware I/O functions
+ *
+ * Copyright (C) 2009-2010 Nippon Telegraph and Telephone Corporation.
+ * Copyright (c) 2011, Red Hat, Inc.
+ *
+ * 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 "qemu-common.h"
+#include "qemu_socket.h"
+#include "qemu-coroutine.h"
+
+int coroutine_fn qemu_co_recvv(int sockfd, struct iovec *iov,
+                               int len, int iov_offset)
+{
+    int total = 0;
+    int ret;
+    while (len) {
+        ret = qemu_recvv(sockfd, iov, len, iov_offset + total);
+        if (ret < 0) {
+            if (errno == EAGAIN) {
+                qemu_coroutine_yield();
+                continue;
+            }
+            if (total == 0) {
+                total = -1;
+            }
+            break;
+        }
+        if (ret == 0) {
+            break;
+        }
+        total += ret, len -= ret;
+    }
+
+    return total;
+}
+
+int coroutine_fn qemu_co_sendv(int sockfd, struct iovec *iov,
+                               int len, int iov_offset)
+{
+    int total = 0;
+    int ret;
+    while (len) {
+        ret = qemu_sendv(sockfd, iov, len, iov_offset + total);
+        if (ret < 0) {
+            if (errno == EAGAIN) {
+                qemu_coroutine_yield();
+                continue;
+            }
+            if (total == 0) {
+                total = -1;
+            }
+            break;
+        }
+        total += ret, len -= ret;
+    }
+
+    return total;
+}
+
+int coroutine_fn qemu_co_recv(int sockfd, void *buf, int len)
+{
+    struct iovec iov;
+
+    iov.iov_base = buf;
+    iov.iov_len = len;
+
+    return qemu_co_recvv(sockfd, &iov, len, 0);
+}
+
+int coroutine_fn qemu_co_send(int sockfd, void *buf, int len)
+{
+    struct iovec iov;
+
+    iov.iov_base = buf;
+    iov.iov_len = len;
+
+    return qemu_co_sendv(sockfd, &iov, len, 0);
+}
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 291cba2eaa..155b05840b 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -35,13 +35,15 @@
 
 #define SOCKET_PATH    "/var/lock/qemu-nbd-%s"
 
-#define NBD_BUFFER_SIZE (1024*1024)
-
-static int sigterm_wfd;
+static NBDExport *exp;
 static int verbose;
 static char *device;
 static char *srcpath;
 static char *sockpath;
+static bool sigterm_reported;
+static bool nbd_started;
+static int shared = 1;
+static int nb_fds;
 
 static void usage(const char *name)
 {
@@ -170,10 +172,8 @@ static int find_partition(BlockDriverState *bs, int partition,
 
 static void termsig_handler(int signum)
 {
-    static int sigterm_reported;
-    if (!sigterm_reported) {
-        sigterm_reported = (write(sigterm_wfd, "", 1) == 1);
-    }
+    sigterm_reported = true;
+    qemu_notify_event();
 }
 
 static void *show_parts(void *arg)
@@ -244,17 +244,38 @@ out:
     return (void *) EXIT_FAILURE;
 }
 
+static int nbd_can_accept(void *opaque)
+{
+    return nb_fds < shared;
+}
+
+static void nbd_client_closed(NBDClient *client)
+{
+    nb_fds--;
+    qemu_notify_event();
+}
+
+static void nbd_accept(void *opaque)
+{
+    int server_fd = (uintptr_t) opaque;
+    struct sockaddr_in addr;
+    socklen_t addr_len = sizeof(addr);
+
+    int fd = accept(server_fd, (struct sockaddr *)&addr, &addr_len);
+    nbd_started = true;
+    if (fd != -1 && nbd_client_new(exp, fd, nbd_client_closed)) {
+        nb_fds++;
+    }
+}
+
 int main(int argc, char **argv)
 {
     BlockDriverState *bs;
     off_t dev_offset = 0;
-    off_t offset = 0;
     uint32_t nbdflags = 0;
     bool disconnect = false;
     const char *bindto = "0.0.0.0";
     int port = NBD_DEFAULT_PORT;
-    struct sockaddr_in addr;
-    socklen_t addr_len = sizeof(addr);
     off_t fd_size;
     const char *sopt = "hVb:o:p:rsnP:c:dvk:e:t";
     struct option lopt[] = {
@@ -282,14 +303,7 @@ int main(int argc, char **argv)
     int flags = BDRV_O_RDWR;
     int partition = -1;
     int ret;
-    int shared = 1;
-    uint8_t *data;
-    fd_set fds;
-    int *sharing_fds;
     int fd;
-    int i;
-    int nb_fds = 0;
-    int max_fd;
     int persistent = 0;
     pthread_t client_thread;
 
@@ -297,12 +311,6 @@ int main(int argc, char **argv)
      * handler ensures that "qemu-nbd -v -c" exits with a nice status code.
      */
     struct sigaction sa_sigterm;
-    int sigterm_fd[2];
-    if (qemu_pipe(sigterm_fd) == -1) {
-        err(EXIT_FAILURE, "Error setting up communication pipe");
-    }
-
-    sigterm_wfd = sigterm_fd[1];
     memset(&sa_sigterm, 0, sizeof(sa_sigterm));
     sa_sigterm.sa_handler = termsig_handler;
     sigaction(SIGTERM, &sa_sigterm, NULL);
@@ -492,16 +500,17 @@ int main(int argc, char **argv)
         err(EXIT_FAILURE, "Could not find partition %d", partition);
     }
 
-    sharing_fds = g_malloc((shared + 1) * sizeof(int));
+    exp = nbd_export_new(bs, dev_offset, fd_size, nbdflags);
 
     if (sockpath) {
-        sharing_fds[0] = unix_socket_incoming(sockpath);
+        fd = unix_socket_incoming(sockpath);
     } else {
-        sharing_fds[0] = tcp_socket_incoming(bindto, port);
+        fd = tcp_socket_incoming(bindto, port);
     }
 
-    if (sharing_fds[0] == -1)
+    if (fd == -1) {
         return 1;
+    }
 
     if (device) {
         int ret;
@@ -516,60 +525,15 @@ int main(int argc, char **argv)
         memset(&client_thread, 0, sizeof(client_thread));
     }
 
-    max_fd = sharing_fds[0];
-    nb_fds++;
-
-    data = qemu_blockalign(bs, NBD_BUFFER_SIZE);
-    if (data == NULL) {
-        errx(EXIT_FAILURE, "Cannot allocate data buffer");
-    }
+    qemu_init_main_loop();
+    qemu_set_fd_handler2(fd, nbd_can_accept, nbd_accept, NULL,
+                         (void *)(uintptr_t)fd);
 
     do {
-        FD_ZERO(&fds);
-        FD_SET(sigterm_fd[0], &fds);
-        for (i = 0; i < nb_fds; i++)
-            FD_SET(sharing_fds[i], &fds);
-
-        do {
-            ret = select(max_fd + 1, &fds, NULL, NULL, NULL);
-        } while (ret == -1 && errno == EINTR);
-        if (ret == -1 || FD_ISSET(sigterm_fd[0], &fds)) {
-            break;
-        }
-
-        if (FD_ISSET(sharing_fds[0], &fds))
-            ret--;
-        for (i = 1; i < nb_fds && ret; i++) {
-            if (FD_ISSET(sharing_fds[i], &fds)) {
-                if (nbd_trip(bs, sharing_fds[i], fd_size, dev_offset,
-                    &offset, nbdflags, data, NBD_BUFFER_SIZE) != 0) {
-                    close(sharing_fds[i]);
-                    nb_fds--;
-                    sharing_fds[i] = sharing_fds[nb_fds];
-                    i--;
-                }
-                ret--;
-            }
-        }
-        /* new connection ? */
-        if (FD_ISSET(sharing_fds[0], &fds)) {
-            if (nb_fds < shared + 1) {
-                sharing_fds[nb_fds] = accept(sharing_fds[0],
-                                             (struct sockaddr *)&addr,
-                                             &addr_len);
-                if (sharing_fds[nb_fds] != -1 &&
-                    nbd_negotiate(sharing_fds[nb_fds], fd_size, nbdflags) != -1) {
-                        if (sharing_fds[nb_fds] > max_fd)
-                            max_fd = sharing_fds[nb_fds];
-                        nb_fds++;
-                }
-            }
-        }
-    } while (persistent || nb_fds > 1);
-    qemu_vfree(data);
+        main_loop_wait(false);
+    } while (!sigterm_reported && (persistent || !nbd_started || nb_fds > 0));
 
-    close(sharing_fds[0]);
-    g_free(sharing_fds);
+    nbd_export_close(exp);
     if (sockpath) {
         unlink(sockpath);
     }
diff --git a/qemu-tool.c b/qemu-tool.c
index 5df7279745..226b6e890e 100644
--- a/qemu-tool.c
+++ b/qemu-tool.c
@@ -16,12 +16,12 @@
 #include "qemu-timer.h"
 #include "qemu-log.h"
 #include "migration.h"
+#include "main-loop.h"
+#include "qemu_socket.h"
+#include "slirp/libslirp.h"
 
 #include <sys/time.h>
 
-QEMUClock *rt_clock;
-QEMUClock *vm_clock;
-
 FILE *logfile;
 
 struct QEMUBH
@@ -57,41 +57,45 @@ void monitor_protocol_event(MonitorEvent event, QObject *data)
 {
 }
 
-int qemu_set_fd_handler2(int fd,
-                         IOCanReadHandler *fd_read_poll,
-                         IOHandler *fd_read,
-                         IOHandler *fd_write,
-                         void *opaque)
+int64 cpu_get_clock(void)
 {
-    return 0;
+    abort();
 }
 
-void qemu_notify_event(void)
+int64 cpu_get_icount(void)
 {
+    abort();
 }
 
-QEMUTimer *qemu_new_timer(QEMUClock *clock, int scale,
-                          QEMUTimerCB *cb, void *opaque)
+void qemu_mutex_lock_iothread(void)
 {
-    return g_malloc(1);
 }
 
-void qemu_free_timer(QEMUTimer *ts)
+void qemu_mutex_unlock_iothread(void)
 {
-    g_free(ts);
 }
 
-void qemu_del_timer(QEMUTimer *ts)
+int use_icount;
+
+void qemu_clock_warp(QEMUClock *clock)
 {
 }
 
-void qemu_mod_timer(QEMUTimer *ts, int64_t expire_time)
+static void __attribute__((constructor)) init_main_loop(void)
 {
+    init_clocks();
+    init_timer_alarm();
+    qemu_clock_enable(vm_clock, false);
 }
 
-int64_t qemu_get_clock_ns(QEMUClock *clock)
+void slirp_select_fill(int *pnfds, fd_set *readfds,
+                       fd_set *writefds, fd_set *xfds)
+{
+}
+
+void slirp_select_poll(fd_set *readfds, fd_set *writefds,
+                       fd_set *xfds, int select_error)
 {
-    return 0;
 }
 
 void migrate_add_blocker(Error *reason)
diff --git a/qemu_socket.h b/qemu_socket.h
index 9e32fac651..fe4cf6ca61 100644
--- a/qemu_socket.h
+++ b/qemu_socket.h
@@ -35,6 +35,7 @@ int inet_aton(const char *cp, struct in_addr *ia);
 /* misc helpers */
 int qemu_socket(int domain, int type, int protocol);
 int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen);
+int socket_set_cork(int fd, int v);
 void socket_set_block(int fd);
 void socket_set_nonblock(int fd);
 int send_all(int fd, const void *buf, int len1);