STREAM(4) 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; sub-
sequent calls generate SIGPIPE signals.
Processing modules may be inserted into streams. These
ioctl calls insert, 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 dis-
cipline named by the integer to which param points. A
census of line discipline 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 containing 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
STREAM(4) STREAM(4)
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 (priority),
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 characters that may be read from this stream
without possible blocking.
TIOCSPGRP
with null param makes this process the head of a pro-
cess 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 pro-
cess group. Child processes inherit the process group
of their parent. Process groups are created only by
explicit use of this call, and not implicitly by open-
ing certain devices. If param is not null, it points
to an integer nominating a process group to receive
signals from this stream.
TIOCGPGRP
stores through param an integer naming the process
group associated with the stream.
TIOCEXCL
STREAM(4) STREAM(4)
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 mes-
sage is understood by devices capable of generating it
(such as asynchronous 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 Edi-
tion 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 direction into data messages, and written mes-
sages into controls. rmesg_ld does the opposite. See
mesg (4).
trc_ld
Helps debug stream line discipline modules.
STREAM(4) STREAM(4)
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.
