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1.1 root 1: .TH STREAM 4
2: .CT 2 comm_proc
3: .SH NAME
4: stream \- communication channels
5: .SH SYNOPSIS
6: .B #include <sys/filio.h>
7: .br
8: .B #include <sys/ttyio.h>
9: .SH DESCRIPTION
10: A stream is a connection between two processes, or between a process
11: and a device.
12: It is referred to by a file descriptor, and ordinary read and write
13: calls apply.
14: When a write
15: call is given on a stream whose other end has disappeared,
16: for example because the process at other end of a pipe has terminated,
17: or a device has hung up, signal
18: .B SIGPIPE
19: is generated; if the signal is ignored,
20: the write call returns error
21: .BR EPIPE .
22: The first 64
23: attempts to read such a disconnected stream
24: return 0;
25: subsequent attempts generate
26: .B SIGPIPE
27: signals.
28: .PP
29: Pipes are streams;
30: so are most communication devices
31: like terminals and networks.
32: .PP
33: Line disciplines may be inserted into a stream
34: to do various sorts of processing.
35: Line disciplines within a stream
36: are identified by their position;
37: level 0 is nearest the process.
38: Line disciplines on
39: one end of a pipe cannot be seen from the other.
40: Line discipline types are integers;
41: a list is given below.
42: .PP
43: These
44: .I ioctl
45: calls,
46: defined in
47: .BR <sys/filio.h> ,
48: manipulate line disciplines:
49: .nr pW \w'\f3FIOPUSHLD 'u
50: .TP \n(pWu
51: .B FIOPUSHLD
52: The third argument points to an integer naming a line discipline;
53: insert that line discipline
54: at level 0.
55: .PD
56: .TP
57: .B FIOINSLD
58: The third argument points to a structure:
59: .RS
60: .LP
61: .EX
62: struct insld {
63: short ld;
64: short level;
65: };
66: .EE
67: .LP
68: Insert the line discipline named by
69: .B ld
70: in the stream
71: at
72: depth
73: .BR level .
74: If there are fewer than
75: .B level
76: line disciplines in the stream,
77: an error is returned.
78: .RE
79: .TP
80: .B FIOPOPLD
81: The third argument points to an integer;
82: remove the line discipline at that level in the stream.
83: A null pointer
84: (the usual case)
85: means level 0.
86: .TP
87: .B FIOLOOKLD
88: The third argument
89: points to an integer;
90: return the type of the line discipline at that level,
91: both in the same integer
92: and as the return value from
93: .IR ioctl .
94: A null pointer means level 0.
95: .PP
96: These
97: .I ioctl
98: calls,
99: also in
100: .BR <sys/filio.h> ,
101: perform other operations on streams:
102: .TP \n(pWu
103: .B FIOSNDFD
104: The third argument points to an integer
105: naming an open file descriptor.
106: Send a reference to that file
107: to the other end of the stream.
108: This works only on pipes.
109: The reference is unaffected by intervening line disciplines;
110: in particular it cannot be intercepted or forged by
111: .IR mesgld (4).
112: .B FIOSNDFD
113: returns immediately;
114: it does not wait for the reference to be received.
115: .TP
116: .B FIORCVFD
117: The third argument points to a structure:
118: .RS
119: .LP
120: .EX
121: struct passfd {
122: int fd;
123: short uid;
124: short gid;
125: short nice;
126: char logname[8];
127: };
128: .EE
129: .PP
130: Receive a file reference sent by
131: .BR FIOSNDFD ;
132: fill in the structure with a file descriptor
133: .B fd
134: for the passed file,
135: and the userid
136: .BR uid ,
137: groupid
138: .BR gid ,
139: login name
140: .BR logname ,
141: and scheduling priority
142: .BR nice
143: of the sending process.
144: The file reference must be the next message in the stream;
145: if data precedes it,
146: .B EIO
147: is returned.
148: If the stream is empty,
149: .B FIORCVFD
150: blocks until data or a file reference arrives.
151: .RE
152: .TP
153: .B FIONREAD
154: The third argument
155: points to an integer;
156: fill it in with the number of characters
157: that may be read from this stream without blocking.
158: .PP
159: These
160: .I ioctl
161: calls also work on streams,
162: but are defined in
163: .BR <sys/ttyio.h>
164: for historic reasons:
165: .TP \n(pWu
166: .B TIOCSPGRP
167: The third argument points to a short integer.
168: If the pointer is null
169: (the usual case),
170: make a new process group for the current process,
171: and associate the group with this stream.
172: If the pointer is not null,
173: it points to a process group id;
174: associate that group with this stream.
175: When the lowest level of a stream
176: receives a signal message
177: (like
178: .B SIGINT
179: or
180: .B SIGQUIT
181: from
182: .IR ttyld (4)),
183: the signal is sent to processes in the associated process group.
184: If the stream is shut down prematurely,
185: the process group is sent
186: .BR SIGHUP .
187: .TP
188: .B TIOCGPGRP
189: The third argument points to a short integer;
190: fill it in with the process group id associated with this stream.
191: 0 means no group.
192: .TP
193: .B TIOCEXCL
194: Mark this stream
195: so that future opens are forbidden
196: except to the super-user
197: or to processes in the associated process group.
198: .TP
199: .B TIOCNXCL
200: Remove the mark left by
201: .BR TIOCEXCL .
202: .TP
203: .B TIOCSBRK
204: Send a break on a serial line.
205: .TP
206: .B TIOCFLUSH
207: Throw away queued data anywhere in the stream.
208: .LP
209: Here is a list of line discipline types.
210: The names refer to global integers
211: defined in the C library.
212: .TP \n(pWu
213: .PD 0
214: .B tty_ld
215: Regular terminal processing,
216: .IR ttyld (4).
217: .TP
218: .B ntty_ld
219: Restricted Berkeley `new tty' terminal processing;
220: see the Berkeley Users Manual.
221: .TP
222: .B cdkp_ld
223: Character-mode Datakit universal receiver protocol,
224: .IR dk (4).
225: .TP
226: .B dkp_ld
227: Block-mode Datakit universal receiver protocol,
228: .IR dk (4).
229: .TP
230: .B rdk_ld
231: .TP
232: .B uxp_ld
233: Datakit protocols used in call setup,
234: .IR dk (4).
235: .TP
236: .B buf_ld
237: Buffering mechanism,
238: .IR bufld (4).
239: .TP
240: .B mesg_ld
241: .TP
242: .B rmesg_ld
243: Turn stream controls into ordinary data and vice versa,
244: .IR mesgld (4).
245: .TP
246: .B conn_ld
247: Make unique connections to a server,
248: .IR connld (4).
249: .TP
250: .B ip_ld
251: .TP
252: .B tcp_ld
253: .TP
254: .B udp_ld
255: Internet protocols,
256: .IR internet (3).
257: .SH SEE ALSO
258: .IR ioctl (2),
259: .IR signal (2),
260: .IR mesgld (4),
261: .IR ipc (3)
262: .br
263: D. M. Ritchie,
264: `A Stream I/O System',
265: this manual, Volume 2
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