AF_IUCV(7)

NAME
AF_IUCV - Sockets for z/VM IUCV and HiperSockets communication

SYNOPSIS
#include <sys/socket.h>
#include <netiucv/iucv.h>

iucv_stream_socket = socket(AF_IUCV, SOCK_STREAM, 0);
iucv_packet_socket = socket(AF_IUCV, SOCK_SEQPACKET, 0);

DESCRIPTION
The AF_IUCV address family provides an addressing mode for communications between applications that run on System z mainframes. This addressing mode can be used for connections through real HiperSockets and through the z/VM Inter-User Communication Vehicle (IUCV).

HiperSockets facilitate connections between applications across LPARs within a System z mainframe. In particular, an application running on an instance of Linux on System z can communicate with:

    •   Itself

    •   Other applications running on the same Linux instance

    •   An application on an instance of Linux on System z in another LPAR

IUCV facilitates connections between applications across z/VM guest virtual machines within a z/VM system. In particular, an application running on Linux on z/VM can communicate with:

    •   Itself

    •   Other applications running on the same Linux instance

    •   Applications running on other instances of Linux on z/VM within the same z/VM system

    •   Applications running on a z/VM guest other than Linux within the same z/VM system

    •   The z/VM control program (CP)

The AF_IUCV address family supports stream-oriented sockets (SOCK_STREAM) and connection-oriented datagram sockets (SOCK_SEQPACKET). Stream-oriented sockets can fragment data over several packets. Sockets of type SOCK_SEQPACKET always map a particular socket write or read operation to a single packet.

  Features
For all instances of Linux on System z, the AF_IUCV address family provides:

    •   Multiple outgoing socket connections for real HiperSockets in layer3 mode

    •   Multiple incoming socket connections for real HiperSockets in layer3 mode

For instances of Linux on z/VM, the AF_IUCV address family also provides:

    •   Multiple outgoing socket connections for IUCV

    •   Multiple incoming socket connections for IUCV

    •   Socket communication with applications utilizing CMS AF_IUCV support

ADDRESS FORMAT
An AF_IUCV socket is represented by the following 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_user_id[8]; /* 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 blanks.

siucv_user_id
    specifies a HiperSockets device or a z/VM guest virtual machine. This specification implicitly sets the connection type for the socket to a HiperSockets connection or to a z/VM IUCV connection. This field must be eight characters long and, if necessary, padded with blanks on the right. For HiperSockets connections, the siucv_user_id field specifies the identifier that is set with the hsuid sysfs attribute of the HiperSockets device. For bind(2) this is the identifier of a local device, and for connect(2) this is the identifier of the HiperSockets device of the communication peer. For IUCV connections, the siucv_user_id field specifies a z/VM user ID. For bind(2) this is the identifier of the local z/VM guest virtual machine, and for connect(2) this is the identifier of the z/VM guest virtual machine for the communication peer.

    Tip:
        For bind(2) you can also specify eight blanks. The AF_IUCV address family support then automatically substitutes the local z/VM user ID for you.

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, and if necessary, padded with blanks on the right. Similar to TCP or UDP ports, application names distinguish distinct applications on the same operating system instance. Do not call bind(2) for names beginning with lnxhvc. These names are reserved for the z/VM IUCV HVC device driver (see also hvc_iucv(9)).

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 for IUCV connections to increase performance when transferring small amounts of data. For HiperSockets connections, this option has no effect. To send data in the parameter list, specify a non-zero integer value.

    Note:
        Use this option with care, older AF_IUCV versions do not support receiving socket data in the parameter list and shut down the socket on which a parameter list message has been received.

SO_MSGLIMIT
    Modifies the message limit for communication paths. The message limit specifies the maximum number of outstanding messages that are allowed for established connections. For IUCV connections this setting can be lowered by z/VM when a connection is established. The message limit is an integer value in range 1 to 65535. The default value is 65535 for IUCV connections and 128 for HiperSockets connections. 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. For IUCV connections, there are two parameters that specify the message limit: getsockopt(2) and the z/VM IUCV MSGLIMIT parameter. If the two parameters specify different values for the message limit, the lower value is used. See the "SETUP FOR IUCV CONNECTIONS" section for setting IUCV MSGLIMIT authorizations.

SO_MSGSIZE
    getsockopt(2) returns the maximum message size a bound AF_IUCV socket can handle. The maximum message size for connections through HiperSockets depends on the MTU size of the underlying HiperSockets connection.
    For sockets that are not yet bound the maximum message size cannot be determined.

ANCILLARY DATA
Ancillary data is sent and received using 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 a type of ancillary data that is supported by the AF_IUCV address family.
For more information see cmsg(3). Currently, the only supported type is:

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 the 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.

SETUP FOR HIPERSOCKETS CONNECTIONS
This section applies to HiperSockets connections and explains the configuration of a HiperSockets device used for AF_IUCV address family support.

To run an AF_IUCV socket application using HiperSockets connections, the socket must be bound to a particular HiperSockets device configured with layer3 mode. Use the hsuid attribute of a HiperSockets device to identify it to the AF_IUCV address family support.

The identifier must adhere to these rules:

    •   It must be 1 to 8 characters.

    •   It must be unique across your environment.

    •   It must not match any z/VM user ID in your environment.

To set an identifier, issue a command like this:

    echo identifier > /sys/devices/qeth/<bus-ID>/hsuid

You can then address this device by specifying the hsuid as the value for the siucv_user_id field in the sockaddr_iucv addressing structure.

For example, to use "MYHOST01" to bind AF_IUCV sockets to the HiperSockets device with bus-ID 0.0.8000, run:

    echo "MYHOST01" > /sys/devices/qeth/0.0.8000/hsuid

SETUP FOR IUCV CONNECTIONS
This section applies to z/VM IUCV connections and provides an overview of the required IUCV statements for your z/VM guest virtual machines. For details and for general IUCV setup information for z/VM guest 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 guest virtual machine to establish a communication path with this z/VM guest virtual machine. With this statement, no further authorization is required for the z/VM guest 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, the maximum, 65535, is used.

  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 system 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 IUCV connections is exceeded for the calling or for the target z/VM guest virtual machine. This error can be temporary and the application might try again after some time. If the error occurs repeatedly, increase the maximum number of connections (for one or both z/VM guest virtual machines). See the "SETUP FOR IUCV CONNECTIONS" section about the required authorization statement. sendmsg (2) called but the maximum number of outstanding messages for the socket connection is reached, for example, if data is available that has not yet been received by the communication peer. If necessary, increase the message limit using the setsockopt(2) function for HiperSockets and IUCV connections. In addition, increase the IUCV message limit as as explained in section "Granting IUCV authorizations".

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

ENODEV
    connect(2) or sendmsg(2) called but the HiperSockets device bound to the AF_IUCV socket does not exist.

ENETDOWN
    connect(2) or sendmsg(2) called but the HiperSockets device bound to the AF_IUCV socket is not activated.

EBADFD
    connect(2) called but for HiperSockets connections the AF_IUCV socket is not bound or, for IUCV connections, the socket is neither in open nor in bound state. bind(2) called but the AF_IUCV socket is no longer in open state. accept(2) called but the AF_IUCV socket is not listening. getsockopt(2) called but the AF_IUCV socket is not bound.

EINVAL
    connect(2) or bind(2) called but the siucv_family field of the specified sockaddr_iucv structure is not set to AF_IUCV. 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 have been 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 latest version of the AF_IUCV address family.

EADDRINUSE
    bind(2) called with an siucv_name already used for another AF_IUCV socket.

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

    •   Support for sending socket data in the parameter list of an IUCV message (SO_IPRMDATA_MSG).

    •   Access the target class of an IUCV message as ancillary data using sendmsg(2) and recvmsg(2).

    •   Support for SOCK_SEQPACKET sockets to facilitate development of native IUCV applications that interact with AF_IUCV.

AF_IUCV, version 1.2

    •   Support for HiperSockets connections.