NAME | SYNOPSIS | DESCRIPTION | ERRORS | VERSIONS | SEE ALSO | COLOPHON

VSOCK(7)                  Linux Programmer's Manual                 VSOCK(7)

NAME         top

       vsock - Linux VSOCK address family

SYNOPSIS         top

       #include <sys/socket.h>
       #include <linux/vm_sockets.h>

       stream_socket = socket(AF_VSOCK, SOCK_STREAM, 0);
       datagram_socket = socket(AF_VSOCK, SOCK_DGRAM, 0);

DESCRIPTION         top

       The VSOCK address family facilitates communication between virtual
       machines and the host they are running on.  This address family is
       used by guest agents and hypervisor services that need a
       communications channel that is independent of virtual machine network
       configuration.

       Valid socket types are SOCK_STREAM and SOCK_DGRAM.  SOCK_STREAM
       provides connection-oriented byte streams with guaranteed, in-order
       delivery.  SOCK_DGRAM provides a connectionless datagram packet
       service with best-effort delivery and best-effort ordering.
       Availability of these socket types is dependent on the underlying
       hypervisor.

       A new socket is created with

           socket(AF_VSOCK, socket_type, 0);

       When a process wants to establish a connection, it calls connect(2)
       with a given destination socket address.  The socket is automatically
       bound to a free port if unbound.

       A process can listen for incoming connections by first binding to a
       socket address using bind(2) and then calling listen(2).

       Data is transmitted using the send(2) or write(2) families of system
       calls and data is received using the recv(2) or read(2) families of
       system calls.

   Address format
       A socket address is defined as a combination of a 32-bit Context
       Identifier (CID) and a 32-bit port number.  The CID identifies the
       source or destination, which is either a virtual machine or the host.
       The port number differentiates between multiple services running on a
       single machine.

           struct sockaddr_vm {
               sa_family_t    svm_family;     /* Address family: AF_VSOCK */
               unsigned short svm_reserved1;
               unsigned int   svm_port;       /* Port # in host byte order */
               unsigned int   svm_cid;        /* Address in host byte order */
           };

       svm_family is always set to AF_VSOCK.  svm_reserved1 is always set to
       0.  svm_port contains the port number in host byte order.  The port
       numbers below 1024 are called privileged ports.  Only a process with
       the CAP_NET_BIND_SERVICE capability may bind(2) to these port num‐
       bers.

       There are several special addresses: VMADDR_CID_ANY (-1U) means any
       address for binding; VMADDR_CID_HYPERVISOR (0) is reserved for ser‐
       vices built into the hypervisor; VMADDR_CID_RESERVED (1) must not be
       used; VMADDR_CID_HOST (2) is the well-known address of the host.

       The special constant VMADDR_PORT_ANY (-1U) means any port number for
       binding.

   Live migration
       Sockets are affected by live migration of virtual machines.  Con‐
       nected SOCK_STREAM sockets become disconnected when the virtual
       machine migrates to a new host.  Applications must reconnect when
       this happens.

       The local CID may change across live migration if the old CID is not
       available on the new host.  Bound sockets are automatically updated
       to the new CID.

   Ioctls
       IOCTL_VM_SOCKETS_GET_LOCAL_CID
              Get the CID of the local machine.  The argument is a pointer
              to an unsigned int.

                  ioctl(socket, IOCTL_VM_SOCKETS_GET_LOCAL_CID, &cid);

              Consider using VMADDR_CID_ANY when binding instead of getting
              the local CID with IOCTL_VM_SOCKETS_GET_LOCAL_CID.

ERRORS         top

       EACCES Unable to bind to a privileged port without the
              CAP_NET_BIND_SERVICE capability.

       EADDRINUSE
              Unable to bind to a port that is already in use.

       EADDRNOTAVAIL
              Unable to find a free port for binding or unable to bind to a
              nonlocal CID.

       EINVAL Invalid parameters.  This includes: attempting to bind a
              socket that is already bound, providing an invalid struct
              sockaddr_vm, and other input validation errors.

       ENOPROTOOPT
              Invalid socket option in setsockopt(2) or getsockopt(2).

       ENOTCONN
              Unable to perform operation on an unconnected socket.

       EOPNOTSUPP
              Operation not supported.  This includes: the MSG_OOB flag that
              is not implemented for the send(2) family of syscalls and
              MSG_PEEK for the recv(2) family of syscalls.

       EPROTONOSUPPORT
              Invalid socket protocol number.  The protocol should always be
              0.

       ESOCKTNOSUPPORT
              Unsupported socket type in socket(2).  Only SOCK_STREAM and
              SOCK_DGRAM are valid.

VERSIONS         top

       Support for VMware (VMCI) has been available since Linux 3.9.  KVM
       (virtio) is supported since Linux 4.8.  Hyper-V is supported since
       Linux 4.14.

SEE ALSO         top

       bind(2), connect(2), listen(2), recv(2), send(2), socket(2),
       capabilities(7)

COLOPHON         top

       This page is part of release 4.16 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                            2017-11-30                         VSOCK(7)