msocket - create an endpoint for communication in a multi-stack environment
/* See NOTES */
int msocket(char * path, int domain, int
type, int protocol);
() creates an endpoint for communication and returns a descriptor
in a multi-stack environment or defines the default stack.
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).
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
|PF_UNIX ", " PF_LOCAL
||IPv4 Internet protocols
||IPv6 Internet protocols
||IPX - Novell protocols
||Kernel user interface device
||ITU-T X.25 / ISO-8208 protocol
||Amateur radio AX.25 protocol
||Access to raw ATM PVCs
||Low level packet interface
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:
- Provides sequenced, reliable, two-way, connection-based
byte streams. An out-of-band data transmission mechanism may be
- Supports datagrams (connectionless, unreliable messages of
a fixed maximum length).
- 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.
- Provides raw network protocol access.
- Provides a reliable datagram layer that does not guarantee
- Obsolete and should not be used in new programs; see
Some socket types may not be implemented by all protocol families; for example,
is not implemented for AF_INET
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
(2) calls. Default stacks get inherited through process creation
(2) and execution execve
(2). When type
the named stack
becames the default stack for all the protocols it supports.
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
(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
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
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
The communications protocols which implement a SOCK_STREAM
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
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.
sockets employ the same system calls as
sockets. The only difference is that read
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.
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.
is an obsolete socket type to receive raw packets directly
from the device driver. Use packet
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
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
. Using F_SETOWN
is equivalent to an ioctl
with the FIOSETOWN
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
The operation of sockets is controlled by socket level options
options are defined in <sys/socket.h>
. The functions
(2) and getsockopt
(2) are used to set and get options,
On success, a file descriptor for the new socket is returned except when
In this latter case 0 is returned on
success. On error, -1 is returned, and errno
is set appropriately.
- Permission to create a socket of the specified type and/or
protocol is denied.
- The implementation does not support the specified address
- Unknown protocol, or protocol family not available.
- Process file table overflow.
- The system limit on the total number of open files has been
- ENOBUFS or ENOMEM
- Insufficient memory is available. The socket cannot be
created until sufficient resources are freed.
- The protocol type or the specified protocol is not
supported within this domain.
Other errors may be generated by the underlying protocol modules.
This is a system call defined for View-OS. It extends socket
in 4.2BSD and conforming to 4.4BSD, POSIX.1-2001. System providing
() do provide also a socket
() call for backward
compatibility. In fact: socket(domain,type,protocol)
is equivalent to
In this way it is generally portable to/from non-BSD systems supporting clones
of the BSD socket layer (including System V variants).
POSIX.1-2001 does not require the inclusion of <sys/types.h>
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
, 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.
is not implemented yet.
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.
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.
Howto's and further information can be found on the project wiki