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1.1 root 1: .\" Copyright (c) 1983 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)fcntl.2 6.4 (Berkeley) 5/22/86
6: .\"
7: .TH FCNTL 2 "May 22, 1986"
8: .UC 5
9: .SH NAME
10: fcntl \- file control
11: .SH SYNOPSIS
12: .nf
13: .ft B
14: #include <fcntl.h>
15: .PP
16: .ft B
17: res = fcntl(fd, cmd, arg)
18: int res;
19: int fd, cmd, arg;
20: .ft R
21: .SH DESCRIPTION
22: .I Fcntl
23: provides for control over descriptors.
24: The argument
25: .I fd
26: is a descriptor to be operated on by
27: .I cmd
28: as follows:
29: .TP 15
30: F_DUPFD
31: Return a new descriptor as follows:
32: .IP
33: Lowest numbered available descriptor greater than or equal to
34: .I arg.
35: .IP
36: Same object references as the original descriptor.
37: .IP
38: New descriptor shares the same file pointer if the object
39: was a file.
40: .IP
41: Same access mode (read, write or read/write).
42: .IP
43: Same file status flags (i.e., both file descriptors
44: share the same file status flags).
45: .IP
46: The close-on-exec flag associated with the new file descriptor
47: is set to remain open across
48: .IR execv (2)
49: system calls.
50: .TP 15
51: F_GETFD
52: Get the close-on-exec flag associated with the file descriptor
53: .IR fd .
54: If the low-order bit is 0, the file will remain open across
55: .IR exec ,
56: otherwise the file will be closed upon execution of
57: .I exec.
58: .TP 15
59: F_SETFD
60: Set the close-on-exec flag associated with
61: .I fd
62: to the low order bit of
63: .I arg
64: (0 or 1 as above).
65: .TP 15
66: F_GETFL
67: Get descriptor status flags, as described below.
68: .TP 15
69: F_SETFL
70: Set descriptor status flags.
71: .TP 15
72: F_GETOWN
73: Get the process ID or process group
74: currently receiving SIGIO and SIGURG
75: signals; process groups are returned
76: as negative values.
77: .TP
78: F_SETOWN
79: Set the process or process group
80: to receive SIGIO and SIGURG signals;
81: process groups are specified by supplying
82: .I arg
83: as negative, otherwise
84: .I arg
85: is interpreted as a process ID.
86: .LP
87: The flags for the F_GETFL and F_SETFL flags are as follows:
88: .TP 15
89: FNDELAY
90: Non-blocking I/O; if no data is available to a
91: .I read
92: call, or if a write operation would block,
93: the call returns -1 with the error EWOULDBLOCK.
94: .TP
95: FAPPEND
96: Force each write to append at the end of file;
97: corresponds to the O_APPEND flag of
98: .IR open (2).
99: .TP
100: FASYNC
101: Enable the SIGIO signal to be sent to the process group
102: when I/O is possible, e.g.,
103: upon availability of data to be read.
104: .SH "RETURN VALUE
105: Upon successful completion, the value returned depends on
106: .I cmd
107: as follows:
108: .sp .5v
109: .nf
110: .ta .25i 1.25i
111: F_DUPFD A new file descriptor.
112: F_GETFD Value of flag (only the low-order bit is defined).
113: F_GETFL Value of flags.
114: F_GETOWN Value of file descriptor owner.
115: other Value other than \-1.
116: .fi
117: .sp .5v
118: Otherwise, a value of \-1 is returned and
119: .I errno
120: is set to indicate the error.
121: .SH ERRORS
122: .I Fcntl
123: will fail if one or more of the following are true:
124: .TP 15
125: [EBADF]
126: .I Fildes
127: is not a valid open file descriptor.
128: .TP 15
129: [EMFILE]
130: .I Cmd
131: is F_DUPFD and the maximum allowed number of file descriptors are currently
132: open.
133: .TP 15
134: [EINVAL]
135: .I Cmd
136: is F_DUPFD and
137: .I arg
138: is negative or greater than the maximum allowable number
139: (see
140: .IR getdtablesize (2)).
141: .TP 15
142: [ESRCH]
143: .I Cmd
144: is F_SETOWN and
145: the process ID given as argument is not in use.
146: .SH "SEE ALSO
147: close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
148: .SH BUGS
149: The asynchronous I/O facilities of FNDELAY and FASYNC
150: are currently available only for tty and socket operations.
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