man7/vsock.7

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  25 .TH VSOCK 7 2017-11-30 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 vsock \- Linux VSOCK address family
  28 .SH SYNOPSIS
  29 .B #include <sys/socket.h>
  30 .br
  31 .B #include <linux/vm_sockets.h>
  32 .PP
  33 .IB stream_socket " = socket(AF_VSOCK, SOCK_STREAM, 0);"
  34 .br
  35 .IB datagram_socket " = socket(AF_VSOCK, SOCK_DGRAM, 0);"
  36 .SH DESCRIPTION
  37 The VSOCK address family facilitates communication between virtual machines and
  38 the host they are running on.
  39 This address family is used by guest agents and
  40 hypervisor services that need a communications channel that is independent of
  41 virtual machine network configuration.
  42 .PP
  43 Valid socket types are
  44 .B SOCK_STREAM
  45 and
  46 .BR SOCK_DGRAM .
  47 .B SOCK_STREAM
  48 provides connection-oriented byte streams with guaranteed, in-order delivery.
  49 .B SOCK_DGRAM
  50 provides a connectionless datagram packet service with best-effort delivery and
  51 best-effort ordering.
  52 Availability of these socket types is dependent on the
  53 underlying hypervisor.
  54 .PP
  55 A new socket is created with
  56 .PP
  57 .in +4n
  58 .EX
  59 socket(AF_VSOCK, socket_type, 0);
  60 .EE
  61 .in
  62 .PP
  63 When a process wants to establish a connection, it calls
  64 .BR connect (2)
  65 with a given destination socket address.
  66 The socket is automatically bound to a free port if unbound.
  67 .PP
  68 A process can listen for incoming connections by first binding to a socket
  69 address using
  70 .BR bind (2)
  71 and then calling
  72 .BR listen (2).
  73 .PP
  74 Data is transmitted using the
  75 .BR send (2)
  76 or
  77 .BR write (2)
  78 families of system calls and data is received using the
  79 .BR recv (2)
  80 or
  81 .BR read (2)
  82 families of system calls.
  83 .SS Address format
  84 A socket address is defined as a combination of a 32-bit Context Identifier
  85 (CID) and a 32-bit port number.
  86 The CID identifies the source or destination,
  87 which is either a virtual machine or the host.
  88 The port number differentiates between multiple services running on
  89 a single machine.
  90 .PP
  91 .in +4n
  92 .EX
  93 struct sockaddr_vm {
  94     sa_family_t    svm_family;     /* Address family: AF_VSOCK */
  95     unsigned short svm_reserved1;
  96     unsigned int   svm_port;       /* Port # in host byte order */
  97     unsigned int   svm_cid;        /* Address in host byte order */
  98 };
  99 .EE
 100 .in
 101 .PP
 102 .I svm_family
 103 is always set to
 104 .BR AF_VSOCK .
 105 .I svm_reserved1
 106 is always set to 0.
 107 .I svm_port
 108 contains the port number in host byte order.
 109 The port numbers below 1024 are called
 110 .IR "privileged ports" .
 111 Only a process with the
 112 .B CAP_NET_BIND_SERVICE
 113 capability may
 114 .BR bind (2)
 115 to these port numbers.
 116 .PP
 117 There are several special addresses:
 118 .B VMADDR_CID_ANY
 119 (\-1U)
 120 means any address for binding;
 121 .B VMADDR_CID_HYPERVISOR
 122 (0) is reserved for services built into the hypervisor;
 123 .B VMADDR_CID_RESERVED
 124 (1) must not be used;
 125 .B VMADDR_CID_HOST
 126 (2)
 127 is the well-known address of the host.
 128 .PP
 129 The special constant
 130 .B VMADDR_PORT_ANY
 131 (\-1U)
 132 means any port number for binding.
 133 .SS Live migration
 134 Sockets are affected by live migration of virtual machines.
 135 Connected
 136 .B SOCK_STREAM
 137 sockets become disconnected when the virtual machine migrates to a new host.
 138 Applications must reconnect when this happens.
 139 .PP
 140 The local CID may change across live migration if the old CID is
 141 not available on the new host.
 142 Bound sockets are automatically updated to the new CID.
 143 .SS Ioctls
 144 .TP
 145 .B IOCTL_VM_SOCKETS_GET_LOCAL_CID
 146 Get the CID of the local machine.
 147 The argument is a pointer to an
 148 .IR "unsigned int" .
 149 .IP
 150 .in +4n
 151 .EX
 152 ioctl(socket, IOCTL_VM_SOCKETS_GET_LOCAL_CID, &cid);
 153 .EE
 154 .in
 155 .IP
 156 Consider using
 157 .B VMADDR_CID_ANY
 158 when binding instead of getting the local CID with
 159 .BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
 160 .SH ERRORS
 161 .TP
 162 .B EACCES
 163 Unable to bind to a privileged port without the
 164 .B CAP_NET_BIND_SERVICE
 165 capability.
 166 .TP
 167 .B EADDRINUSE
 168 Unable to bind to a port that is already in use.
 169 .TP
 170 .B EADDRNOTAVAIL
 171 Unable to find a free port for binding or unable to bind to a nonlocal CID.
 172 .TP
 173 .B EINVAL
 174 Invalid parameters.
 175 This includes:
 176 attempting to bind a socket that is already bound, providing an invalid struct
 177 .IR sockaddr_vm ,
 178 and other input validation errors.
 179 .TP
 180 .B ENOPROTOOPT
 181 Invalid socket option in
 182 .BR setsockopt (2)
 183 or
 184 .BR getsockopt (2).
 185 .TP
 186 .B ENOTCONN
 187 Unable to perform operation on an unconnected socket.
 188 .TP
 189 .B EOPNOTSUPP
 190 Operation not supported.
 191 This includes:
 192 the
 193 .B MSG_OOB
 194 flag that is not implemented for the
 195 .BR send (2)
 196 family of syscalls and
 197 .B MSG_PEEK
 198 for the
 199 .BR recv (2)
 200 family of syscalls.
 201 .TP
 202 .B EPROTONOSUPPORT
 203 Invalid socket protocol number.
 204 The protocol should always be 0.
 205 .TP
 206 .B ESOCKTNOSUPPORT
 207 Unsupported socket type in
 208 .BR socket (2).
 209 Only
 210 .B SOCK_STREAM
 211 and
 212 .B SOCK_DGRAM
 213 are valid.
 214 .SH VERSIONS
 215 Support for VMware (VMCI) has been available since Linux 3.9.
 216 KVM (virtio) is supported since Linux 4.8.
 217 Hyper-V is supported since Linux 4.14.
 218 .SH SEE ALSO
 219 .BR bind (2),
 220 .BR connect (2),
 221 .BR listen (2),
 222 .BR recv (2),
 223 .BR send (2),
 224 .BR socket (2),
 225 .BR capabilities (7)