term% cat index.txt STREAM(4) Kernel Interfaces Manual STREAM(4)
NAME
stream - stream I/O control calls
SYNOPSIS
#include <sys/ioctl.h>
ioctl(fd, code, param)
union universe *param;
DESCRIPTION
A stream is a connection between two processes, or between a process
and a device. It is referred to by a file descriptor, and ordinary
read and write calls apply. When a write(2) call is given on a stream
whose other end has disappeared, for example because the process at
other end of a pipe has terminated, or a device has hung up, a SIGPIPE
signal is generated; if the signal is ignored, the write call returns
error EPIPE. The first several (currently 64) read(2) calls on such a
disconnected streams return 0; subsequent calls generate SIGPIPE sig‐
nals.
Processing modules may be inserted into streams. These ioctl calls in‐
sert, delete, inspect, and perform operations for stream IO modules.
They apply to the file descriptor of any open stream object: terminal,
network connection, pipe. The param argument is a general pointer
which, for these calls, is usually null or a pointer to int. The codes
are
FIOPUSHLD
inserts, at the near end of the stream, the line discipline named
by the integer to which param points. A census of line disci‐
pline modules is given below.
FIOINSLD
inserts a named line discipline at a given level in a stack of
such modules on the stream. Param points to a structure contain‐
ing two short integers respectively naming the line discipline
and the level. A level of 0 could be accomplished by FIOPUSHLD.
This call is under construction and may not be available yet.
FIOPOPLD
pops (removes) the nearest line discipline module, if param is
null. If it points to an integer, the line discipline at that
level is removed. The integer 0 corresponds to a null param, and
(as with FIOINSLD) the non-null case may not be handled yet.
FIOLOOKLD
returns the number of the topmost line discipline in the stack.
If param is not null but instead points to an integer, the line
discipline at that level is returned in the same integer. As
with push and pop, the non-null case may not be handled yet.
FIOSNDFD
sends the integer file descriptor pointed to by param to the
process on the other end of the pipe whose file descriptor is fd.
FIORCVFD
delivers a structure pointed to by param:
struct passfd {
union {
int fd;
} f;
short uid;
short gid;
short nice;
short fill;
};
The call blocks until there is something in the stream. If data
is present, it returns EIO. If the FIOSNDFD call has sent a file
descriptor to the other end of the pipe, this call fills in the
user and group ID of the sending process, its niceness (prior‐
ity), and a file descriptor for the file being sent; this file is
now open in the calling process.
FIONREAD
stores, in the integer pointed to by param, the number of charac‐
ters that may be read from this stream without possible blocking.
TIOCSPGRP
with null param makes this process the head of a process group
and makes this stream its control stream. When signals, such as
hangup, interrupt, and quit, arrive at a control stream, they are
sent to its process group. Child processes inherit the process
group of their parent. Process groups are created only by ex‐
plicit use of this call, and not implicitly by opening certain
devices. If param is not null, it points to an integer nominat‐
ing a process group to receive signals from this stream.
TIOCGPGRP
stores through param an integer naming the process group associ‐
ated with the stream.
TIOCEXCL
marks this stream as inaccessible except by the super-user or by
processes in the group associated with this stream.
TIOCNXCL
removes the inaccessibility of the stream.
TIOCSBRK
generates a message requesting a line break. The message is un‐
derstood by devices capable of generating it (such as asynchro‐
nous character devices) and ignored otherwise.
TIOCFLUSH
generates a message causing downstream modules to throw away any
queued characters, if possible. It applies to both input and
output queues.
Here is a list of available line discipline modules. The magic numbers
are collected in the standard library, and are accessible under the
following names:
tty_ld
Terminal processing according to standard Seventh Edition rules;
see ttyld(4).
ntty_ld
Terminal processing according to (modified) Berkeley `new tty'
rules; see Berkeley Users Manual.
cdkp_ld
Character-mode Datakit URP protocol.
dkp_ld
Block-mode Datakit URP protocol.
rdk_ld
Special Datakit protocol used in connection setup.
pk_ld Packet-driver protocol (obsolete).
buf_ld
Buffering mechanism; see bufld(4).
mesg_ld, rmesg_ld
Mesg_ld turns stream control blocks arriving in the read direc‐
tion into data messages, and written messages into controls.
rmesg_ld does the opposite. See mesg (4).
trc_ld
Helps debug stream line discipline modules.
conn_ld
For making unique connections to servers. See connld(4).
ip_ld, tcp_ld, udp_ld, arp_ld
Internet protocols; see inet(3).
SEE ALSO
ioctl(2)
D. M. Ritchie, `A Stream I/O System' BLTJ, October, 1984
DIAGNOSTICS
-1 is returned for errors.
STREAM(4)