.\" Copyright (c) 2008 Renzo Davoli
.\"
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.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1998, 1999 by Andi Kleen <ak@muc.de>
.\" Modified 2002-07-17 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2008-04-23 by Renzo Davoli <renzo@cs.unibo.it>
.\"
.TH MSOCKET 2VIEWOS 2008-04-23 "View-OS" "Linux/View-OS Programmer's Manual"
.SH NAME
msocket \- create an endpoint for communication in a multi-stack environment
.SH SYNOPSIS
.BR "#include <sys/types.h>" "          /* See NOTES */"
.br
.B #include <msocket.h>
.sp
.BI "int msocket(char * " path ", int " domain ", int " type ", int " protocol );
.SH DESCRIPTION
.BR msocket ()
creates an endpoint for communication and returns a descriptor in a multi-stack
environment or defines the default stack.
.PP
The
.I 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).
.PP
The
.I domain
parameter specifies a communication domain; this selects the protocol
family which will be used for communication.
These families are defined in
.IR <sys/socket.h> .
The currently understood formats include:
.TS
tab(:);
l l l.
Name:Purpose:Man page
T{
.BR PF_UNIX ", " PF_LOCAL
T}:T{
Local communication
T}:T{
.BR unix (7)
T}
T{
.B PF_INET
T}:IPv4 Internet protocols:T{
.BR ip (7)
T}
T{
.B PF_INET6
T}:IPv6 Internet protocols:T{
.BR ipv6 (7)
T}
T{
.B PF_IPX
T}:IPX \- Novell protocols:
T{
.B PF_NETLINK
T}:T{
Kernel user interface device
T}:T{
.BR netlink (7)
T}
T{
.B PF_X25
T}:ITU-T X.25 / ISO-8208 protocol:T{
.BR x25 (7)
T}
T{
.B PF_AX25
T}:T{
Amateur radio AX.25 protocol
T}:
T{
.B PF_ATMPVC
T}:Access to raw ATM PVCs:
T{
.B PF_APPLETALK
T}:Appletalk:T{
.BR ddp (7)
T}
T{
.B PF_PACKET
T}:T{
Low level packet interface
T}:T{
.BR packet (7)
T}
.TE
.PP
The socket has the indicated
.IR type ,
which specifies the communication semantics or 
.B SOCK_DEFAULT 
to define the standard stack for the specified domain(s).
Currently defined types
are:
.TP
.B SOCK_STREAM
Provides sequenced, reliable, two-way, connection-based byte streams.
An out-of-band data transmission mechanism may be supported.
.TP
.B SOCK_DGRAM
Supports datagrams (connectionless, unreliable messages of a fixed
maximum length).
.TP
.B 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.
.TP
.B SOCK_RAW
Provides raw network protocol access.
.TP
.B SOCK_RDM
Provides a reliable datagram layer that does not guarantee ordering.
.TP
.B SOCK_PACKET
Obsolete and should not be used in new programs;
see
.BR packet (7).
.PP
Some socket types may not be implemented by all protocol families;
for example,
.B SOCK_SEQPACKET
is not implemented for
.BR AF_INET .
.PP
When 
.IR type 
is
.B 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 
.BR socket (2)
calls.
Default stacks get inherited through process creation
.BR fork (2)
and execution
.BR execve (2).
When 
.IR type 
is
.B SOCK_DEFAULT
and 
.IR domain
is
.B PF_UNSPEC
the named stack becames the default stack for all the protocols it supports.
.PP
The
.I 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
.I 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 \*(lqcommunication domain\*(rq
in which communication is to take place; see
.BR protocols (5).
See
.BR getprotoent (3)
on how to map protocol name strings to protocol numbers.
.PP
Sockets of type
.B SOCK_STREAM
are full-duplex byte streams, similar to pipes.
They do not preserve
record boundaries.
A stream socket must be in
a
.I connected
state before any data may be sent or received on it.
A connection to
another socket is created with a
.BR connect (2)
call.
Once connected, data may be transferred using
.BR read (2)
and
.BR write (2)
calls or some variant of the
.BR send (2)
and
.BR recv (2)
calls.
When a session has been completed a
.BR close (2)
may be performed.
Out-of-band data may also be transmitted as described in
.BR send (2)
and received as described in
.BR recv (2).
.PP
The communications protocols which implement a
.B 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
.B SO_KEEPALIVE
is enabled on the socket the protocol checks in a protocol-specific
manner if the other end is still alive.
A
.B 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.
.B SOCK_SEQPACKET
sockets employ the same system calls as
.B SOCK_STREAM
sockets.
The only difference is that
.BR 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.
.PP
.B SOCK_DGRAM
and
.B SOCK_RAW
sockets allow sending of datagrams to correspondents named in
.BR sendto (2)
calls.
Datagrams are generally received with
.BR recvfrom (2),
which returns the next datagram along with the address of its sender.
.PP
.B SOCK_PACKET
is an obsolete socket type to receive raw packets directly from the
device driver.
Use
.BR packet (7)
instead.
.PP
An
.BR fcntl (2)
.B F_SETOWN
operation can be used to specify a process or process group to receive a
.B SIGURG
signal when the out-of-band data arrives or
.B SIGPIPE
signal when a
.B 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
.BR SIGIO .
Using
.B F_SETOWN
is equivalent to an
.BR ioctl (2)
call with the
.B FIOSETOWN
or
.B SIOCSPGRP
argument.
.PP
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
.B IP_RECVERR
in
.BR ip (7).
.PP
The operation of sockets is controlled by socket level
.IR options .
These options are defined in
.IR <sys/socket.h> .
The functions
.BR setsockopt (2)
and
.BR getsockopt (2)
are used to set and get options, respectively.
.SH "RETURN VALUE"
On success, a file descriptor for the new socket is returned except when
.IR type
is
.BR SOCK_DEFAULT.
In this latter case 0 is returned on success.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Permission to create a socket of the specified type and/or protocol
is denied.
.TP
.B EAFNOSUPPORT
The implementation does not support the specified address family.
.TP
.B EINVAL
Unknown protocol, or protocol family not available.
.TP
.B EMFILE
Process file table overflow.
.TP
.B ENFILE
The system limit on the total number of open files has been reached.
.TP
.BR ENOBUFS " or " ENOMEM
Insufficient memory is available.
The socket cannot be
created until sufficient resources are freed.
.TP
.B EPROTONOSUPPORT
The protocol type or the specified protocol is not
supported within this domain.
.PP
Other errors may be generated by the underlying protocol modules.
.SH "CONFORMING TO"
This is a system call defined for View-OS. It extends 
.BR socket (), 
appeared in 4.2BSD and conforming to
4.4BSD, POSIX.1-2001.
System providing
.BR msocket ()
do provide also a 
.BR socket ()
call for backward compatibility.
In fact:
.BR "socket(domain,type,protocol)"
is equivalent to
.BR "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).
.SH NOTES
POSIX.1-2001 does not require the inclusion of
.IR <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
.BR PF_UNIX ,
.BR PF_INET ,
etc., while
.B 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
.I <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.
.SH BUGS
.B SOCK_UUCP
is not implemented yet.
.\"SH EXAMPLE
.\"An example of the use of
.\"BR socket ()
.\"s shown in
.\"BR getaddrinfo (3).
.SH "SEE ALSO"
.BR socket (2),
.BR accept (2),
.BR bind (2),
.BR connect (2),
.BR fcntl (2),
.BR getpeername (2),
.BR getsockname (2),
.BR getsockopt (2),
.BR ioctl (2),
.BR listen (2),
.BR read (2),
.BR recv (2),
.BR select (2),
.BR send (2),
.BR shutdown (2),
.BR socketpair (2),
.BR write (2),
.BR getprotoent (3),
.BR ip (7),
.BR socket (7),
.BR tcp (7),
.BR udp (7),
.BR unix (7)
.PP
.SH COLOPHON
This page has been modified from 
.BR socket (2)
page of release 2.79 of the Linux. In fact
.BR msocket (2)
is an extension of this call.
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
.PP
View-OS is a project of the Computer Science Department, University of
Bologna. Project Leader: Renzo Davoli. 
.br
<http://www.sourceforge.net/projects/view-os>

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