[unix-history] / usr / src / lib / libc / sys / fcntl.2

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)fcntl.2	6.2 (Berkeley) %G%
.\"
.TH FCNTL 2 ""
.UC 5
.SH NAME
fcntl \- file control
.SH SYNOPSIS
.nf
.ft B
#include <fcntl.h>
.PP
.ft B
res = fcntl(fd, cmd, arg)
int res;
int fd, cmd, arg;
.ft R
.SH DESCRIPTION
.I Fcntl
provides for control over descriptors.
The argument
.I fd
is a descriptor to be operated on by
.I cmd
as follows:
.TP 15
F_DUPFD
Return a new descriptor as follows:
.IP
Lowest numbered available descriptor greater than or equal to
.I arg.
.IP
Same object references as the original descriptor.
.IP
New descriptor shares the same file pointer if the object
was a file.
.IP
Same access mode (read, write or read/write).
.IP
Same file status flags (i.e., both file descriptors
share the same file status flags).
.IP
The close-on-exec flag associated with the new file descriptor
is set to remain open across
.IR execv (2)
system calls.
.TP 15
F_GETFD
Get the close-on-exec flag associated with the file descriptor
.IR fd .
If the low-order bit is 0, the file will remain open across
.IR exec ,
otherwise the file will be closed upon execution of
.I exec.
.TP 15
F_SETFD
Set the close-on-exec flag associated with
.I fd
to the low order bit of
.I arg
(0 or 1 as above).
.TP 15
F_GETFL
Get descriptor status flags, as described below.
.TP 15
F_SETFL
Set descriptor status flags.
.TP 15
F_GETOWN
Get the process ID or process group
currently receiving SIGIO and SIGURG
signals; process groups are returned
as negative values.
.TP
F_SETOWN
Set the process or process group
to receive SIGIO and SIGURG signals;
process groups are specified by supplying
.I arg
as negative, otherwise 
.I arg
is interpreted as a process ID.
.LP
The flags for the F_GETFL and F_SETFL flags are as follows:
.TP 15
FNDELAY
Non-blocking I/O; if no data is available to a
.I read
call, or if a write operation would block,
the call returns -1 with the error EWOULDBLOCK.
.TP
FAPPEND
Force each write to append at the end of file;
corresponds to the O_APPEND flag of
.IR open (2).
.TP
FASYNC
Enable the SIGIO signal to be sent to the process group
when I/O is possible, e.g.
upon availability of data to be read.
.SH "RETURN VALUE
Upon successful completion, the value returned depends on
.I cmd
as follows:
.sp .5v
.nf
.ta .25i 1.25i
	F_DUPFD	A new file descriptor.
	F_GETFD	Value of flag (only the low-order bit is defined).
	F_GETFL	Value of flags.
	F_GETOWN	Value of file descriptor owner.
	other	Value other than \-1.
.fi
.sp .5v
Otherwise, a value of \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.I Fcntl
will fail if one or more of the following are true:
.TP 15
[EBADF]
.I Fildes
is not a valid open file descriptor.
.TP 15
[EMFILE]
.I Cmd
is F_DUPFD and the maximum allowed number of file descriptors are currently
open.
.TP 15
[EINVAL]
.I Cmd
is F_DUPFD and
.I arg
is negative or greater the maximum allowable number
(see
.IR getdtablesize (2)).
.SH "SEE ALSO
close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
.SH BUGS
The asynchronous I/O facilities of FNDELAY and FASYNC
are currently available only for tty and socket operations.
Commit	Line	Data
c24fefdc KM	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	.\"
1df601cf	5	.\" @(#)fcntl.2 6.2 (Berkeley) %G%
c24fefdc	6	.\"
4ef918f1	7	.TH FCNTL 2 ""
c24fefdc KM	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 the maximum allowable number
139	(see
140	.IR getdtablesize (2)).
141	.SH "SEE ALSO
142	close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
143	.SH BUGS
144	The asynchronous I/O facilities of FNDELAY and FASYNC
1df601cf	145	are currently available only for tty and socket operations.