vsock(7) - Linux manual page (original) (raw)
vsock(7) Miscellaneous Information Manual vsock(7)
NAME top
vsock - Linux VSOCK address familySYNOPSIS top
**#include <sys/socket.h>**
**#include <linux/vm_sockets.h>**
_streamsocket_ **= socket(AF_VSOCK, SOCK_STREAM, 0);**
_datagramsocket_ **= 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)](../man2/connect.2.html) 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)](../man2/bind.2.html) and then calling [listen(2)](../man2/listen.2.html).
Data is transmitted using the [send(2)](../man2/send.2.html) or [write(2)](../man2/write.2.html) families of
system calls and data is received using the [recv(2)](../man2/recv.2.html) or [read(2)](../man2/read.2.html)
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)];
};
_svmfamily_ is always set to **AF_VSOCK**. _svmreserved1_ is always set
to 0. _svmport_ 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)](../man2/bind.2.html) to
these port numbers. _svmzero_ 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.Ioctls The following ioctls are available on the /dev/vsock device.
**IOCTL_VM_SOCKETS_GET_LOCAL_CID**
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
**VMADDR_CID_LOCAL**.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
_sockaddrvm_, and other input validation errors.
**ENOPROTOOPT**
Invalid socket option in [setsockopt(2)](../man2/setsockopt.2.html) or [getsockopt(2)](../man2/getsockopt.2.html).
**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)](../man2/send.2.html) family of syscalls
and **MSG_PEEK** for the [recv(2)](../man2/recv.2.html) family of syscalls.
**EPROTONOSUPPORT**
Invalid socket protocol number. The protocol should always
be 0.
**ESOCKTNOSUPPORT**
Unsupported socket type in [socket(2)](../man2/socket.2.html). 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)](../man2/bind.2.html), [connect(2)](../man2/connect.2.html), [listen(2)](../man2/listen.2.html), [recv(2)](../man2/recv.2.html), [send(2)](../man2/send.2.html), [socket(2)](../man2/socket.2.html),
[capabilities(7)](../man7/capabilities.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-05-02 vsock(7)
Pages that refer to this page:lsfd(1), systemd-ssh-proxy(1), trace-cmd-agent(1), socket(2), org.freedesktop.hostname1(5), address_families(7), systemd-ssh-generator(8)