Comtrol eCos - Manual (Page 576)

Chapter 38. TCP/IP Library Reference
described here.
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. However, it is possible that many
protocols may exist, in which case a particular protocol must be speci-
fied in this manner. The protocol number to use is particular to the
communication domain in which communication is to take place; see
protocols(5). A value of 0 for protocol will let the system select an
appropriate protocol for the requested socket type.
Sockets of type SOCK_STREAM are full-duplex byte streams, similar to
pipes. 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 used to 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 broken and
calls will indicate an error with -1 returns and with ETIMEDOUT as the
specific code in the global variable errno. The protocols optionally
keep sockets “warm” by forcing transmissions roughly every minute in
the absence of other activity. An error is then indicated if no response
can be elicited on an otherwise idle connection for a extended period
(e.g., 5 minutes). A SIGPIPE signal is raised if a process sends on a
broken stream; this causes naive processes, which do not handle the sig-
nal, to exit.
SOCK_SEQPACKET sockets employ the same system calls as SOCK_STREAM sock-
ets. The only difference is that read(2) calls will return only the
amount of data requested, and any remaining in the arriving packet will
be discarded.
SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspon-
dents named in send(2) calls. Datagrams are generally received with
recvfrom(2), which returns the next datagram with its return address.
An fcntl(2) call can be used to specify a process group to receive a
SIGURG signal when the out-of-band data arrives. It may also enable non-
blocking I/O and asynchronous notification of I/O events via SIGIO.
The operation of sockets is controlled by socket level options. These
options are defined in the file < sys/socket.h>. setsockopt(2) and
getsockopt(2) are used to set and get options, respectively.
RETURN VALUES
A -1 is returned if an error occurs, otherwise the return value is a
descriptor referencing the socket.
ERRORS
472