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VSOCK(7) Linux Programmer's Manual VSOCK(7)
NAME
vsock - Linux VSOCK address family
SYNOPSIS
#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
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 configu-
ration.
Valid socket types are SOCK_STREAM and SOCK_DGRAM. SOCK_STREAM provides connection-ori-
ented byte streams with guaranteed, in-order delivery. SOCK_DGRAM provides a connection-
less datagram packet service with best-effort delivery and best-effort ordering. Avail-
ability 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 destina-
tion 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 re-
ceived 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 vir-
tual machine or the host. The port number differentiates between multiple services run-
ning 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 con-
tains the port number in host byte order. The port numbers below 1024 are called privi-
leged 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_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. 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.
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
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
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
bind(2), connect(2), listen(2), recv(2), send(2), socket(2), capabilities(7)
COLOPHON
This page is part of release 5.05 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 2020-02-09 VSOCK(7)
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