vsock(7) — Linux manual page


vsock(7)            Miscellaneous Information 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 */
               unsigned char  svm_zero[sizeof(struct sockaddr) -
                                       sizeof(sa_family_t) -
                                       sizeof(unsigned short) -
                                       sizeof(unsigned int) -
                                       sizeof(unsigned int)];

       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 numbers.  svm_zero must be zero-filled.

       There are several special addresses: VMADDR_CID_ANY (-1U) means
       any address for binding; VMADDR_CID_HYPERVISOR (0) is reserved
       for services built into the hypervisor; VMADDR_CID_LOCAL (1) is
       the well-known address for local communication (loopback);
       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.
       Connected 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.

       The following ioctls are available on the /dev/vsock device.

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

                  ioctl(fd, 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.

   Local communication
       VMADDR_CID_LOCAL (1) directs packets to the same host that
       generated them.  This is useful for testing applications on a
       single host and for debugging.

       The local CID obtained with IOCTL_VM_SOCKETS_GET_LOCAL_CID can be
       used for the same purpose, but it is preferable to use

ERRORS         top

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

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

              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.

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

              Unable to perform operation on an unconnected socket.

              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.

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

              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.

       VMADDR_CID_LOCAL is supported since Linux 5.6.  Local
       communication in the guest and on the host is available since
       Linux 5.6.  Previous versions supported only local communication
       within a guest (not on the host), and with only some transports
       (VMCI and virtio).

SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                       vsock(7)

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