nbd_connect_vsock - connect to NBD server over AF_VSOCK protocol


 #include <libnbd.h>

 int nbd_connect_vsock (
       struct nbd_handle *h, uint32_t cid, uint32_t port


Connect (synchronously) over the AF_VSOCK protocol from a virtual machine to an NBD server, usually running on the host. The cid and port parameters specify the server address. Usually cid should be 2 (to connect to the host), and port might be 10809 or another port number assigned to you by the host administrator.

Not all systems support AF_VSOCK; to determine if libnbd was built on a system with vsock support, see nbd_supports_vsock(3).

This call returns when the connection has been made. By default, this proceeds all the way to transmission phase, but nbd_set_opt_mode(3) can be used for manual control over option negotiation performed before transmission phase.


If the call is successful the function returns 0.


On error -1 is returned.

Refer to "ERROR HANDLING" in libnbd(3) for how to get further details of the error.

The following parameters must not be NULL: h. For more information see "Non-NULL parameters" in libnbd(3).


nbd_connect_vsock can be called when the handle is in the following state:

 │ Handle created, before connecting   │ ✅ allowed              │
 │ Connecting                          │ ❌ error                │
 │ Connecting & handshaking (opt_mode) │ ❌ error                │
 │ Connected to the server             │ ❌ error                │
 │ Connection shut down                │ ❌ error                │
 │ Handle dead                         │ ❌ error                │


This function first appeared in libnbd 1.2.

If you need to test if this function is available at compile time check if the following macro is defined:



nbd_aio_connect_vsock(3), nbd_create(3), nbd_set_opt_mode(3), nbd_supports_vsock(3), libnbd(3).


Eric Blake

Richard W.M. Jones


Copyright Red Hat


This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library 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 Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA