diff --git a/nbd/client.c b/nbd/client.c
index a58fb02cb4..6b74a628f1 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -86,9 +86,9 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
 
 */
 
-/* Discard length bytes from channel.  Return -errno on failure, or
- * the amount of bytes consumed. */
-static ssize_t drop_sync(QIOChannel *ioc, size_t size)
+/* Discard length bytes from channel.  Return -errno on failure and 0 on
+ * success*/
+static int drop_sync(QIOChannel *ioc, size_t size)
 {
     ssize_t ret = 0;
     char small[1024];
@@ -96,14 +96,13 @@ static ssize_t drop_sync(QIOChannel *ioc, size_t size)
 
     buffer = sizeof(small) >= size ? small : g_malloc(MIN(65536, size));
     while (size > 0) {
-        ssize_t count = read_sync(ioc, buffer, MIN(65536, size));
+        ssize_t count = MIN(65536, size);
+        ret = read_sync(ioc, buffer, MIN(65536, size));
 
-        if (count <= 0) {
+        if (ret < 0) {
             goto cleanup;
         }
-        assert(count <= size);
         size -= count;
-        ret += count;
     }
 
  cleanup:
@@ -136,12 +135,12 @@ static int nbd_send_option_request(QIOChannel *ioc, uint32_t opt,
     stl_be_p(&req.option, opt);
     stl_be_p(&req.length, len);
 
-    if (write_sync(ioc, &req, sizeof(req)) != sizeof(req)) {
+    if (write_sync(ioc, &req, sizeof(req)) < 0) {
         error_setg(errp, "Failed to send option request header");
         return -1;
     }
 
-    if (len && write_sync(ioc, (char *) data, len) != len) {
+    if (len && write_sync(ioc, (char *) data, len) < 0) {
         error_setg(errp, "Failed to send option request data");
         return -1;
     }
@@ -170,7 +169,7 @@ static int nbd_receive_option_reply(QIOChannel *ioc, uint32_t opt,
                                     nbd_opt_reply *reply, Error **errp)
 {
     QEMU_BUILD_BUG_ON(sizeof(*reply) != 20);
-    if (read_sync(ioc, reply, sizeof(*reply)) != sizeof(*reply)) {
+    if (read_sync(ioc, reply, sizeof(*reply)) < 0) {
         error_setg(errp, "failed to read option reply");
         nbd_send_opt_abort(ioc);
         return -1;
@@ -219,7 +218,7 @@ static int nbd_handle_reply_err(QIOChannel *ioc, nbd_opt_reply *reply,
             goto cleanup;
         }
         msg = g_malloc(reply->length + 1);
-        if (read_sync(ioc, msg, reply->length) != reply->length) {
+        if (read_sync(ioc, msg, reply->length) < 0) {
             error_setg(errp, "failed to read option error message");
             goto cleanup;
         }
@@ -321,7 +320,7 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, bool *match,
         nbd_send_opt_abort(ioc);
         return -1;
     }
-    if (read_sync(ioc, &namelen, sizeof(namelen)) != sizeof(namelen)) {
+    if (read_sync(ioc, &namelen, sizeof(namelen)) < 0) {
         error_setg(errp, "failed to read option name length");
         nbd_send_opt_abort(ioc);
         return -1;
@@ -334,7 +333,7 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, bool *match,
         return -1;
     }
     if (namelen != strlen(want)) {
-        if (drop_sync(ioc, len) != len) {
+        if (drop_sync(ioc, len) < 0) {
             error_setg(errp, "failed to skip export name with wrong length");
             nbd_send_opt_abort(ioc);
             return -1;
@@ -343,14 +342,14 @@ static int nbd_receive_list(QIOChannel *ioc, const char *want, bool *match,
     }
 
     assert(namelen < sizeof(name));
-    if (read_sync(ioc, name, namelen) != namelen) {
+    if (read_sync(ioc, name, namelen) < 0) {
         error_setg(errp, "failed to read export name");
         nbd_send_opt_abort(ioc);
         return -1;
     }
     name[namelen] = '\0';
     len -= namelen;
-    if (drop_sync(ioc, len) != len) {
+    if (drop_sync(ioc, len) < 0) {
         error_setg(errp, "failed to read export description");
         nbd_send_opt_abort(ioc);
         return -1;
@@ -477,7 +476,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         goto fail;
     }
 
-    if (read_sync(ioc, buf, 8) != 8) {
+    if (read_sync(ioc, buf, 8) < 0) {
         error_setg(errp, "Failed to read data");
         goto fail;
     }
@@ -503,7 +502,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         goto fail;
     }
 
-    if (read_sync(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
+    if (read_sync(ioc, &magic, sizeof(magic)) < 0) {
         error_setg(errp, "Failed to read magic");
         goto fail;
     }
@@ -515,8 +514,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         uint16_t globalflags;
         bool fixedNewStyle = false;
 
-        if (read_sync(ioc, &globalflags, sizeof(globalflags)) !=
-            sizeof(globalflags)) {
+        if (read_sync(ioc, &globalflags, sizeof(globalflags)) < 0) {
             error_setg(errp, "Failed to read server flags");
             goto fail;
         }
@@ -534,8 +532,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         }
         /* client requested flags */
         clientflags = cpu_to_be32(clientflags);
-        if (write_sync(ioc, &clientflags, sizeof(clientflags)) !=
-            sizeof(clientflags)) {
+        if (write_sync(ioc, &clientflags, sizeof(clientflags)) < 0) {
             error_setg(errp, "Failed to send clientflags field");
             goto fail;
         }
@@ -573,13 +570,13 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
         }
 
         /* Read the response */
-        if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) {
+        if (read_sync(ioc, &s, sizeof(s)) < 0) {
             error_setg(errp, "Failed to read export length");
             goto fail;
         }
         *size = be64_to_cpu(s);
 
-        if (read_sync(ioc, flags, sizeof(*flags)) != sizeof(*flags)) {
+        if (read_sync(ioc, flags, sizeof(*flags)) < 0) {
             error_setg(errp, "Failed to read export flags");
             goto fail;
         }
@@ -596,14 +593,14 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
             goto fail;
         }
 
-        if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) {
+        if (read_sync(ioc, &s, sizeof(s)) < 0) {
             error_setg(errp, "Failed to read export length");
             goto fail;
         }
         *size = be64_to_cpu(s);
         TRACE("Size is %" PRIu64, *size);
 
-        if (read_sync(ioc, &oldflags, sizeof(oldflags)) != sizeof(oldflags)) {
+        if (read_sync(ioc, &oldflags, sizeof(oldflags)) < 0) {
             error_setg(errp, "Failed to read export flags");
             goto fail;
         }
@@ -619,7 +616,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
     }
 
     TRACE("Size is %" PRIu64 ", export flags %" PRIx16, *size, *flags);
-    if (zeroes && drop_sync(ioc, 124) != 124) {
+    if (zeroes && drop_sync(ioc, 124) < 0) {
         error_setg(errp, "Failed to read reserved block");
         goto fail;
     }
@@ -744,7 +741,6 @@ int nbd_disconnect(int fd)
 ssize_t nbd_send_request(QIOChannel *ioc, NBDRequest *request)
 {
     uint8_t buf[NBD_REQUEST_SIZE];
-    ssize_t ret;
 
     TRACE("Sending request to server: "
           "{ .from = %" PRIu64", .len = %" PRIu32 ", .handle = %" PRIu64
@@ -759,16 +755,7 @@ ssize_t nbd_send_request(QIOChannel *ioc, NBDRequest *request)
     stq_be_p(buf + 16, request->from);
     stl_be_p(buf + 24, request->len);
 
-    ret = write_sync(ioc, buf, sizeof(buf));
-    if (ret < 0) {
-        return ret;
-    }
-
-    if (ret != sizeof(buf)) {
-        LOG("writing to socket failed");
-        return -EINVAL;
-    }
-    return 0;
+    return write_sync(ioc, buf, sizeof(buf));
 }
 
 ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply *reply)
@@ -777,7 +764,7 @@ ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply *reply)
     uint32_t magic;
     ssize_t ret;
 
-    ret = read_sync(ioc, buf, sizeof(buf));
+    ret = read_sync_eof(ioc, buf, sizeof(buf));
     if (ret <= 0) {
         return ret;
     }
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index f43d990a05..e6bbc7c4b4 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -94,7 +94,13 @@
 #define NBD_ENOSPC     28
 #define NBD_ESHUTDOWN  108
 
-static inline ssize_t read_sync(QIOChannel *ioc, void *buffer, size_t size)
+/* read_sync_eof
+ * Tries to read @size bytes from @ioc. Returns number of bytes actually read.
+ * May return a value >= 0 and < size only on EOF, i.e. when iteratively called
+ * qio_channel_readv() returns 0. So, there are no needs to call read_sync_eof
+ * iteratively.
+ */
+static inline ssize_t read_sync_eof(QIOChannel *ioc, void *buffer, size_t size)
 {
     struct iovec iov = { .iov_base = buffer, .iov_len = size };
     /* Sockets are kept in blocking mode in the negotiation phase.  After
@@ -105,12 +111,32 @@ static inline ssize_t read_sync(QIOChannel *ioc, void *buffer, size_t size)
     return nbd_wr_syncv(ioc, &iov, 1, size, true);
 }
 
-static inline ssize_t write_sync(QIOChannel *ioc, const void *buffer,
-                                 size_t size)
+/* read_sync
+ * Reads @size bytes from @ioc. Returns 0 on success.
+ */
+static inline int read_sync(QIOChannel *ioc, void *buffer, size_t size)
+{
+    ssize_t ret = read_sync_eof(ioc, buffer, size);
+
+    if (ret >= 0 && ret != size) {
+        ret = -EINVAL;
+    }
+
+    return ret < 0 ? ret : 0;
+}
+
+/* write_sync
+ * Writes @size bytes to @ioc. Returns 0 on success.
+ */
+static inline int write_sync(QIOChannel *ioc, const void *buffer, size_t size)
 {
     struct iovec iov = { .iov_base = (void *) buffer, .iov_len = size };
 
-    return nbd_wr_syncv(ioc, &iov, 1, size, false);
+    ssize_t ret = nbd_wr_syncv(ioc, &iov, 1, size, false);
+
+    assert(ret < 0 || ret == size);
+
+    return ret < 0 ? ret : 0;
 }
 
 struct NBDTLSHandshakeData {
diff --git a/nbd/server.c b/nbd/server.c
index 924a1fe2db..1e1096c762 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -112,7 +112,7 @@ static gboolean nbd_negotiate_continue(QIOChannel *ioc,
     return TRUE;
 }
 
-static ssize_t nbd_negotiate_read(QIOChannel *ioc, void *buffer, size_t size)
+static int nbd_negotiate_read(QIOChannel *ioc, void *buffer, size_t size)
 {
     ssize_t ret;
     guint watch;
@@ -130,8 +130,7 @@ static ssize_t nbd_negotiate_read(QIOChannel *ioc, void *buffer, size_t size)
 
 }
 
-static ssize_t nbd_negotiate_write(QIOChannel *ioc, const void *buffer,
-                                   size_t size)
+static int nbd_negotiate_write(QIOChannel *ioc, const void *buffer, size_t size)
 {
     ssize_t ret;
     guint watch;
@@ -148,24 +147,24 @@ static ssize_t nbd_negotiate_write(QIOChannel *ioc, const void *buffer,
     return ret;
 }
 
-static ssize_t nbd_negotiate_drop_sync(QIOChannel *ioc, size_t size)
+static int nbd_negotiate_drop_sync(QIOChannel *ioc, size_t size)
 {
-    ssize_t ret, dropped = size;
+    ssize_t ret;
     uint8_t *buffer = g_malloc(MIN(65536, size));
 
     while (size > 0) {
-        ret = nbd_negotiate_read(ioc, buffer, MIN(65536, size));
+        size_t count = MIN(65536, size);
+        ret = nbd_negotiate_read(ioc, buffer, count);
         if (ret < 0) {
             g_free(buffer);
             return ret;
         }
 
-        assert(ret <= size);
-        size -= ret;
+        size -= count;
     }
 
     g_free(buffer);
-    return dropped;
+    return 0;
 }
 
 /* Basic flow for negotiation
@@ -206,22 +205,22 @@ static int nbd_negotiate_send_rep_len(QIOChannel *ioc, uint32_t type,
           type, opt, len);
 
     magic = cpu_to_be64(NBD_REP_MAGIC);
-    if (nbd_negotiate_write(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
+    if (nbd_negotiate_write(ioc, &magic, sizeof(magic)) < 0) {
         LOG("write failed (rep magic)");
         return -EINVAL;
     }
     opt = cpu_to_be32(opt);
-    if (nbd_negotiate_write(ioc, &opt, sizeof(opt)) != sizeof(opt)) {
+    if (nbd_negotiate_write(ioc, &opt, sizeof(opt)) < 0) {
         LOG("write failed (rep opt)");
         return -EINVAL;
     }
     type = cpu_to_be32(type);
-    if (nbd_negotiate_write(ioc, &type, sizeof(type)) != sizeof(type)) {
+    if (nbd_negotiate_write(ioc, &type, sizeof(type)) < 0) {
         LOG("write failed (rep type)");
         return -EINVAL;
     }
     len = cpu_to_be32(len);
-    if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
+    if (nbd_negotiate_write(ioc, &len, sizeof(len)) < 0) {
         LOG("write failed (rep data length)");
         return -EINVAL;
     }
@@ -256,7 +255,7 @@ nbd_negotiate_send_rep_err(QIOChannel *ioc, uint32_t type,
     if (ret < 0) {
         goto out;
     }
-    if (nbd_negotiate_write(ioc, msg, len) != len) {
+    if (nbd_negotiate_write(ioc, msg, len) < 0) {
         LOG("write failed (error message)");
         ret = -EIO;
     } else {
@@ -287,15 +286,15 @@ static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
     }
 
     len = cpu_to_be32(name_len);
-    if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
+    if (nbd_negotiate_write(ioc, &len, sizeof(len)) < 0) {
         LOG("write failed (name length)");
         return -EINVAL;
     }
-    if (nbd_negotiate_write(ioc, name, name_len) != name_len) {
+    if (nbd_negotiate_write(ioc, name, name_len) < 0) {
         LOG("write failed (name buffer)");
         return -EINVAL;
     }
-    if (nbd_negotiate_write(ioc, desc, desc_len) != desc_len) {
+    if (nbd_negotiate_write(ioc, desc, desc_len) < 0) {
         LOG("write failed (description buffer)");
         return -EINVAL;
     }
@@ -309,7 +308,7 @@ static int nbd_negotiate_handle_list(NBDClient *client, uint32_t length)
     NBDExport *exp;
 
     if (length) {
-        if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+        if (nbd_negotiate_drop_sync(client->ioc, length) < 0) {
             return -EIO;
         }
         return nbd_negotiate_send_rep_err(client->ioc,
@@ -340,7 +339,7 @@ static int nbd_negotiate_handle_export_name(NBDClient *client, uint32_t length)
         LOG("Bad length received");
         goto fail;
     }
-    if (nbd_negotiate_read(client->ioc, name, length) != length) {
+    if (nbd_negotiate_read(client->ioc, name, length) < 0) {
         LOG("read failed");
         goto fail;
     }
@@ -373,7 +372,7 @@ static QIOChannel *nbd_negotiate_handle_starttls(NBDClient *client,
     TRACE("Setting up TLS");
     ioc = client->ioc;
     if (length) {
-        if (nbd_negotiate_drop_sync(ioc, length) != length) {
+        if (nbd_negotiate_drop_sync(ioc, length) < 0) {
             return NULL;
         }
         nbd_negotiate_send_rep_err(ioc, NBD_REP_ERR_INVALID, NBD_OPT_STARTTLS,
@@ -437,8 +436,7 @@ static int nbd_negotiate_options(NBDClient *client)
         ...           Rest of request
     */
 
-    if (nbd_negotiate_read(client->ioc, &flags, sizeof(flags)) !=
-        sizeof(flags)) {
+    if (nbd_negotiate_read(client->ioc, &flags, sizeof(flags)) < 0) {
         LOG("read failed");
         return -EIO;
     }
@@ -464,8 +462,7 @@ static int nbd_negotiate_options(NBDClient *client)
         uint32_t clientflags, length;
         uint64_t magic;
 
-        if (nbd_negotiate_read(client->ioc, &magic, sizeof(magic)) !=
-            sizeof(magic)) {
+        if (nbd_negotiate_read(client->ioc, &magic, sizeof(magic)) < 0) {
             LOG("read failed");
             return -EINVAL;
         }
@@ -476,14 +473,14 @@ static int nbd_negotiate_options(NBDClient *client)
         }
 
         if (nbd_negotiate_read(client->ioc, &clientflags,
-                               sizeof(clientflags)) != sizeof(clientflags)) {
+                               sizeof(clientflags)) < 0)
+        {
             LOG("read failed");
             return -EINVAL;
         }
         clientflags = be32_to_cpu(clientflags);
 
-        if (nbd_negotiate_read(client->ioc, &length, sizeof(length)) !=
-            sizeof(length)) {
+        if (nbd_negotiate_read(client->ioc, &length, sizeof(length)) < 0) {
             LOG("read failed");
             return -EINVAL;
         }
@@ -513,7 +510,7 @@ static int nbd_negotiate_options(NBDClient *client)
                 return -EINVAL;
 
             default:
-                if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+                if (nbd_negotiate_drop_sync(client->ioc, length) < 0) {
                     return -EIO;
                 }
                 ret = nbd_negotiate_send_rep_err(client->ioc,
@@ -551,7 +548,7 @@ static int nbd_negotiate_options(NBDClient *client)
                 return nbd_negotiate_handle_export_name(client, length);
 
             case NBD_OPT_STARTTLS:
-                if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+                if (nbd_negotiate_drop_sync(client->ioc, length) < 0) {
                     return -EIO;
                 }
                 if (client->tlscreds) {
@@ -570,7 +567,7 @@ static int nbd_negotiate_options(NBDClient *client)
                 }
                 break;
             default:
-                if (nbd_negotiate_drop_sync(client->ioc, length) != length) {
+                if (nbd_negotiate_drop_sync(client->ioc, length) < 0) {
                     return -EIO;
                 }
                 ret = nbd_negotiate_send_rep_err(client->ioc,
@@ -659,12 +656,12 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
             TRACE("TLS cannot be enabled with oldstyle protocol");
             goto fail;
         }
-        if (nbd_negotiate_write(client->ioc, buf, sizeof(buf)) != sizeof(buf)) {
+        if (nbd_negotiate_write(client->ioc, buf, sizeof(buf)) < 0) {
             LOG("write failed");
             goto fail;
         }
     } else {
-        if (nbd_negotiate_write(client->ioc, buf, 18) != 18) {
+        if (nbd_negotiate_write(client->ioc, buf, 18) < 0) {
             LOG("write failed");
             goto fail;
         }
@@ -679,7 +676,7 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
         stq_be_p(buf + 18, client->exp->size);
         stw_be_p(buf + 26, client->exp->nbdflags | myflags);
         len = client->no_zeroes ? 10 : sizeof(buf) - 18;
-        if (nbd_negotiate_write(client->ioc, buf + 18, len) != len) {
+        if (nbd_negotiate_write(client->ioc, buf + 18, len) < 0) {
             LOG("write failed");
             goto fail;
         }
@@ -702,11 +699,6 @@ static ssize_t nbd_receive_request(QIOChannel *ioc, NBDRequest *request)
         return ret;
     }
 
-    if (ret != sizeof(buf)) {
-        LOG("read failed");
-        return -EINVAL;
-    }
-
     /* Request
        [ 0 ..  3]   magic   (NBD_REQUEST_MAGIC)
        [ 4 ..  5]   flags   (NBD_CMD_FLAG_FUA, ...)
@@ -737,7 +729,6 @@ static ssize_t nbd_receive_request(QIOChannel *ioc, NBDRequest *request)
 static ssize_t nbd_send_reply(QIOChannel *ioc, NBDReply *reply)
 {
     uint8_t buf[NBD_REPLY_SIZE];
-    ssize_t ret;
 
     reply->error = system_errno_to_nbd_errno(reply->error);
 
@@ -754,16 +745,7 @@ static ssize_t nbd_send_reply(QIOChannel *ioc, NBDReply *reply)
     stl_be_p(buf + 4, reply->error);
     stq_be_p(buf + 8, reply->handle);
 
-    ret = write_sync(ioc, buf, sizeof(buf));
-    if (ret < 0) {
-        return ret;
-    }
-
-    if (ret != sizeof(buf)) {
-        LOG("writing to socket failed");
-        return -EINVAL;
-    }
-    return 0;
+    return write_sync(ioc, buf, sizeof(buf));
 }
 
 #define MAX_NBD_REQUESTS 16
@@ -1067,7 +1049,7 @@ static ssize_t nbd_co_send_reply(NBDRequestData *req, NBDReply *reply,
         rc = nbd_send_reply(client->ioc, reply);
         if (rc >= 0) {
             ret = write_sync(client->ioc, req->data, len);
-            if (ret != len) {
+            if (ret < 0) {
                 rc = -EIO;
             }
         }
@@ -1141,7 +1123,7 @@ static ssize_t nbd_co_receive_request(NBDRequestData *req,
     if (request->type == NBD_CMD_WRITE) {
         TRACE("Reading %" PRIu32 " byte(s)", request->len);
 
-        if (read_sync(client->ioc, req->data, request->len) != request->len) {
+        if (read_sync(client->ioc, req->data, request->len) < 0) {
             LOG("reading from socket failed");
             rc = -EIO;
             goto out;