NAME¶

iucv, AF_IUCV - Sockets for z/VM IUCV communication

SYNOPSIS¶

#include <sys/socket.h> iucv_stream_socket = socket(AF_IUCV, SOCK_STREAM, 0); iucv_packet_socket = socket(AF_IUCV, SOCK_SEQPACKET, 0);

DESCRIPTION¶

The Inter-User Communication Vehicle (IUCV) is a z/VM communication facility that enables a program running in one z/VM guest virtual machine to communicate with another z/VM guest virtual machine, or with the control program (CP), or even with itself. The AF_IUCV address family provides communication and addressing in the IUCV domain. In the IUCV domain, address spaces or virtual machines can use the socket interface to communicate with other virtual machines or address spaces within the same z/VM guest operating system. AF_IUCV connects socket applications running on different Linux guest operating systems, or it connects a Linux application to another socket application running in another z/VM guest operating system (like z/VM CMS). The AF_IUCV address family supports stream-oriented sockets (SOCK_STREAM) and connection-oriented datagram sockets (SOCK_SEQPACKET). Stream-oriented sockets fragment data over several native IUCV messages, whereas sockets of type SOCK_SEQPACKET map a particular socket write or read operation to a single native IUCV message.

Features¶

The AF_IUCV address family provides:

•

Multiple outgoing socket connections from a Linux guest operating system.

•

Multiple incoming socket connections to a Linux guest operating system.

•

Socket communication with applications utilizing CMS AF_IUCV support.

ADDRESS FORMAT¶

#define AF_IUCV    32

struct sockaddr_iucv {
    sa_family_t    siucv_family;     /* AF_IUCV */
    unsigned short siucv_port;       /* reserved */
    unsigned int   siucv_addr;       /* reserved */
    char           siucv_nodeid[8];  /* reserved */
    char           siucv_userid[8];  /* guest user id */
    char           siucv_name[8];    /* application name */
};

siucv_family

is set to AF_IUCV (= 32)

siucv_port, siucv_addr, siucv_nodeid

are reserved for future use. The siucv_port and siucv_addr fields must be zero. The siucv_nodeid field must be set to exactly eight blank characters.

siucv_userid

is set to the z/VM user ID of the Linux guest virtual machine running the application that owns the address. The field must be eight characters long, padded with blanks on the right.

 

For bind(2), siucv_userid must contain blanks only to allow AF_IUCV to set the z/VM user ID of the Linux guest operating system.

siucv_name

is set to the application name by which the socket is known. Servers advertise application names and clients use these application names to connect to servers. This field must be eight characters long, padded with blanks on the right.

SOCKET OPTIONS¶

Socket options can be set with setsockopt(2) and read with getsockopt(2) by specifying SOL_IUCV as the socket level.

SO_IPRMDATA_MSG

Enables the application to send up to seven bytes of socket data in the parameter list of an IUCV message. Use this option to increase performance when transferring small amounts of data.

 

To send data in the parameter list, specify a non-zero integer value.

 

SO_MSGLIMIT

Modifies the message limit for new IUCV communication paths. The message limit specifies the maximum number of outstanding messages that are allowed for established connections. This setting can be lowered by z/VM when an IUCV connection is established.

 

The message limit is an integer value in range 1 to 65535. The default value is 65535.

 

The message limit must be set before connect(2) or listen(2) is called for sockets.

 

For sockets that are already connected or listening for connections, the message limit cannot be changed.

 

New sockets created by accept(2) inherit the message limit that has been set for the listening socket.

 

getsockopt(2) returns the default message limit or the limit that has been set. For connected sockets, the current message limit is returned. The current message limit is assigned by z/VM for each connection and it depends on the IUCV MSGLIMIT statement specified for the z/VM guest virtual machine. The current message limit is the lower value of the socket option and the value specified for the IUCV MSGLIMIT statement.

 

See the SECURITY section below for setting IUCV MSGLIMIT authorizations.

ANCILLARY DATA¶

Ancillary data is sent and received using the sendmsg(2) and recvmsg(2). To send ancillary data, set the cmsg_level field of struct cmsghdr to SOL_IUCV and the cmsg_type field to the type. For more information see cmsg(3).

SCM_IUCV_TRGCLS

Send or receive IUCV target class information. The IUCV target class can be used to classify and identify an IUCV message at IUCV protocol level. If the target class is not specified as ancillary data, it is set to zero.

 

The target class is a number of type uint32_t.

SECURITY¶

This section provides an overview of the required IUCV statements for your z/VM guest virtual machine. For details and for general IUCV setup information for z/VM guests virtual machines see z/VM CP Programming Services and z/VM CP Planning and Administration.

Granting IUCV authorizations¶

Use the IUCV directory control statement to grant the necessary authorizations.

IUCV ALLOW

allows any other z/VM virtual machine to establish a communication path with this z/VM virtual machine. With this statement, no further authorization is required in the z/VM virtual machine that initiates the communication.

IUCV ANY

allows this z/VM guest virtual machine to establish a communication path with any other z/VM guest virtual machine.

IUCV user_ID

allows this z/VM guest virtual machine to establish a communication path to the z/VM guest virtual machine with the z/VM user ID user_ID.

You can specify multiple IUCV statements. To any of these IUCV statements you can append the MSGLIMIT limit parameter. limit specifies the maximum number of outstanding messages that are allowed for each connection authorized by this statement. If no value is specified for MSGLIMIT, AF_IUCV requests 65535, which is the maximum supported by IUCV.

Setting a connection limit¶

Use the OPTION statement to limit the number of concurrent connections.

OPTION MAXCONN maxno

maxno specifies the maximum number of IUCV connections allowed for this virtual machine. The default is 64. The maximum is 65535.

Example¶

These sample statements allow any z/VM guest virtual machine to connect to your z/VM guest virtual machine with a maximum of 10000 outstanding messages for each incoming connection. Your z/VM guest virtual machine is permitted to connect to all other z/VM guest virtual machines. The total number of connections for your z/VM guest virtual machine cannot exceed 100.

IUCV ALLOW MSGLIMIT 10000
IUCV ANY
OPTION MAXCONN 100

ERRORS¶

Several socket operations return error conditions that have a special meaning in the context of AF_IUCV. Those error conditions, and the respective descriptions are listed below. See the manual page of the respective socket operation for a complete list of errors.

ECONNREFUSED

connect(2) called but the target z/VM guest virtual machine is not listening on the application name.

ENETUNREACH

connect(2) called but the target z/VM guest virtual machine is not logged on. Ensure that the z/VM guest virtual machine to which your application wants to connect is logged on.

EAGAIN

connect(2) called but the maximum number of connections is exceeded for the calling or for the target z/VM guest virtual machine. This error can be temporary and the application may try again after some time. If the error occurs repeatedly, try to increase the maximum number of connections (for one or both z/VM guest virtual machines). See the SECURITY section about the required authorization statement.

 

sendmsg (2) called but the maximum number of outstanding IUCV messages for the socket connection is reached; i.e. there are data available that has not yet been received by the communication partner.

 

If necessary, change the IUCV message limit as explained in section "IUCV AUTHORIZATIONS".

EACCES

connect(2) called but the calling z/VM guest virtual machine is missing IUCV authorization. See the SECURITY section about required IUCV authorizations.

EINVAL

connect(2) or bind(2) called but the AF_IUCV setting in the siucv_family field of the passed address is missing.

 

listen(2) called but the AF_IUCV socket has not yet been bound to an address. Always call bind(2) before listen(2).

 

setsockopt(2) called with option SO_MSGLIMIT for sockets that are already connected.

ENOPROTOOPT

setsockopt(2), or getsockopt(2) called but the socket level has not been set to SOL_IUCV, or the specified socket option is not supported.

EOPNOTSUPP

sendmsg(2) or recvmsg(2) might be called with the MSG_OOB flag set. AF_IUCV does not support sending or receiving out-of-band data on its sockets.

 

For SOCK_SEQPACKET sockets, sendmsg(2) called without the MSG_EOR flag set. AF_IUCV does not support segmentation, and thus, the "end-of-record" ( MSG_EOR) flag must always be set.

EPROTONOSUPPORT

socket(2) called with a protocol that is not supported. The socket protocol parameter must be either zero or PF_IUCV.

EAFNOSUPPORT

socket(2) called with AF_IUCV but the AF_IUCV address family is not supported by the current Linux kernel. Ensure that your Linux kernel has been compiled with support for the AF_IUCV address family.

Other errors can be generated by the generic socket layer. See the respective manual pages for more information.

SEE ALSO¶

connect(2), recvmsg(2), sendmsg(2), socket(2), setsockopt(2), getsockopt(2), cmsg(3), socket(7) Linux on System z - Device Drivers, Features, and Commands z/VM CP Planning and Administration z/VM CP Programming Services

HISTORY¶

AF_IUCV, version 1.0

Initial version.

AF_IUCV, version 1.1