Ubuntu Manpage: msocket - create an endpoint for communication in a multi-stack environment

NAME

       msocket - create an endpoint for communication in a multi-stack environment

SYNOPSIS

       #include <sys/types.h>          /* See NOTES */
       #include <msocket.h>

       int msocket(char * path, int domain, int type, int protocol);

DESCRIPTION

msocket() creates an endpoint for communication and returns a descriptor in a multi-stack
environment or defines the default stack.

The path parameter selects the stack used for the call. The path must refer to a stack
special file (S_IFSTACK). When path is NULL, the default stack gets used. It is possible
to specify a default network stack for each domain (see SOCK_DEFAULT below).

The domain parameter specifies a communication domain; this selects the protocol family
which will be used for communication. These families are defined in <sys/socket.h>. The
currently understood formats include:

Name Purpose Man page
PF_UNIX, PF_LOCAL Local communication unix(7)
PF_INET IPv4 Internet protocols ip(7)
PF_INET6 IPv6 Internet protocols ipv6(7)
PF_IPX IPX - Novell protocols
PF_NETLINK Kernel user interface device netlink(7)
PF_X25 ITU-T X.25 / ISO-8208 protocol x25(7)
PF_AX25 Amateur radio AX.25 protocol
PF_ATMPVC Access to raw ATM PVCs
PF_APPLETALK Appletalk ddp(7)
PF_PACKET Low level packet interface packet(7)

The socket has the indicated type, which specifies the communication semantics or
SOCK_DEFAULT to define the standard stack for the specified domain(s). Currently defined
types are:

SOCK_STREAM
Provides sequenced, reliable, two-way, connection-based byte streams. An out-of-
band data transmission mechanism may be supported.

SOCK_DGRAM
Supports datagrams (connectionless, unreliable messages of a fixed maximum length).

SOCK_SEQPACKET
Provides a sequenced, reliable, two-way connection-based data transmission path for
datagrams of fixed maximum length; a consumer is required to read an entire packet
with each input system call.

SOCK_RAW
Provides raw network protocol access.

SOCK_RDM
Provides a reliable datagram layer that does not guarantee ordering.

SOCK_PACKET
Obsolete and should not be used in new programs; see packet(7).

Some socket types may not be implemented by all protocol families; for example,
SOCK_SEQPACKET is not implemented for AF_INET.

When type is SOCK_DEFAULT msocket does not define any communication endpoint, instead it
defines the stack that will be used for the following msocket calls with NULL path, or for
the following obsolete socket(2) calls. Default stacks get inherited through process
creation fork(2) and execution execve(2). When type is SOCK_DEFAULT and domain is
PF_UNSPEC the named stack becames the default stack for all the protocols it supports.

The protocol specifies a particular protocol to be used with the socket. Normally only a
single protocol exists to support a particular socket type within a given protocol family,
in which case protocol can be specified as 0. However, it is possible that many protocols
may exist, in which case a particular protocol must be specified in this manner. The
protocol number to use is specific to the “communication domain” in which communication is
to take place; see protocols(5). See getprotoent(3) on how to map protocol name strings
to protocol numbers.

Sockets of type SOCK_STREAM are full-duplex byte streams, similar to pipes. They do not
preserve record boundaries. A stream socket must be in a connected state before any data
may be sent or received on it. A connection to another socket is created with a
connect(2) call. Once connected, data may be transferred using read(2) and write(2) calls
or some variant of the send(2) and recv(2) calls. When a session has been completed a
close(2) may be performed. Out-of-band data may also be transmitted as described in
send(2) and received as described in recv(2).

The communications protocols which implement a SOCK_STREAM ensure that data is not lost or
duplicated. If a piece of data for which the peer protocol has buffer space cannot be
successfully transmitted within a reasonable length of time, then the connection is
considered to be dead. When SO_KEEPALIVE is enabled on the socket the protocol checks in
a protocol-specific manner if the other end is still alive. A SIGPIPE signal is raised if
a process sends or receives on a broken stream; this causes naive processes, which do not
handle the signal, to exit. SOCK_SEQPACKET sockets employ the same system calls as
SOCK_STREAM sockets. The only difference is that read(2) calls will return only the
amount of data requested, and any data remaining in the arriving packet will be discarded.
Also all message boundaries in incoming datagrams are preserved.

SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspondents named in
sendto(2) calls. Datagrams are generally received with recvfrom(2), which returns the
next datagram along with the address of its sender.

SOCK_PACKET is an obsolete socket type to receive raw packets directly from the device
driver. Use packet(7) instead.

An fcntl(2) F_SETOWN operation can be used to specify a process or process group to
receive a SIGURG signal when the out-of-band data arrives or SIGPIPE signal when a
SOCK_STREAM connection breaks unexpectedly. This operation may also be used to set the
process or process group that receives the I/O and asynchronous notification of I/O events
via SIGIO. Using F_SETOWN is equivalent to an ioctl(2) call with the FIOSETOWN or
SIOCSPGRP argument.

When the network signals an error condition to the protocol module (e.g., using a ICMP
message for IP) the pending error flag is set for the socket. The next operation on this
socket will return the error code of the pending error. For some protocols it is possible
to enable a per-socket error queue to retrieve detailed information about the error; see
IP_RECVERR in ip(7).

The operation of sockets is controlled by socket level options. These options are defined
in <sys/socket.h>. The functions setsockopt(2) and getsockopt(2) are used to set and get
options, respectively.

RETURN VALUE

       On  success,  a  file  descriptor  for  the  new  socket  is  returned except when type is
       SOCK_DEFAULT.  In this latter case 0 is returned on success.  On error,  -1  is  returned,
       and errno is set appropriately.

ERRORS

       EACCES Permission to create a socket of the specified type and/or protocol is denied.

       EAFNOSUPPORT
              The implementation does not support the specified address family.

       EINVAL Unknown protocol, or protocol family not available.

       EMFILE Process file table overflow.

       ENFILE The system limit on the total number of open files has been reached.

       ENOBUFS or ENOMEM
              Insufficient  memory  is  available.  The socket cannot be created until sufficient
              resources are freed.

       EPROTONOSUPPORT
              The protocol type or the specified protocol is not supported within this domain.

       Other errors may be generated by the underlying protocol modules.

CONFORMING TO

       This is a system call defined for View-OS. It extends socket(),  appeared  in  4.2BSD  and
       conforming to 4.4BSD, POSIX.1-2001.  System providing msocket() do provide also a socket()
       call for backward compatibility.  In fact: socket(domain,type,protocol) is  equivalent  to
       msocket(NULL,domain,type,protocol)

       In  this way it is generally portable to/from non-BSD systems supporting clones of the BSD
       socket layer (including System V variants).

NOTES

       POSIX.1-2001 does not require the inclusion of <sys/types.h>, and this header file is  not
       required  on  Linux.   However, some historical (BSD) implementations required this header
       file, and portable applications are probably wise to include it.

       The manifest constants used under 4.x BSD for  protocol  families  are  PF_UNIX,  PF_INET,
       etc., while AF_UNIX etc. are used for address families.  However, already the BSD man page
       promises: "The protocol  family  generally  is  the  same  as  the  address  family",  and
       subsequent standards use AF_* everywhere.

       The  header file <sys/types.h> is only required for libc4 or earlier.  Some packages, like
       util-linux, claim portability to all Linux versions and libraries.   They  certainly  need
       this header file.

BUGS

       SOCK_UUCP is not implemented yet.

COLOPHON

       This  page  has  been  modified  from socket(2) page of release 2.79 of the Linux. In fact
       msocket(2) is an extension of  this  call.   man-pages  project.   A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

       View-OS is a project of the Computer Science Department, University  of  Bologna.  Project
       Leader: Renzo Davoli.
       <http://www.sourceforge.net/projects/view-os>

       Howto's and further information can be found on the project wiki
       <wiki.virtualsquare.org>.