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

.\" Copyright (c) 1983 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms are permitted
.\" provided that the above copyright notice and this paragraph are
.\" duplicated in all such forms and that any documentation,
.\" advertising materials, and other materials related to such
.\" distribution and use acknowledge that the software was developed
.\" by the University of California, Berkeley.  The name of the
.\" University may not be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\"	@(#)fcntl.2	6.5 (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 than the maximum allowable number
(see
.IR getdtablesize (2)).
.TP 15
[ESRCH]
.I Cmd
is F_SETOWN and
the process ID given as argument is not in use.
.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
88b3ccf2 KB	1	.\" Copyright (c) 1983 The Regents of the University of California.
88b3ccf2 KB	2	.\" All rights reserved.
c24fefdc	3	.\"
88b3ccf2 KB	4	.\" Redistribution and use in source and binary forms are permitted
	5	.\" provided that the above copyright notice and this paragraph are
	6	.\" duplicated in all such forms and that any documentation,
	7	.\" advertising materials, and other materials related to such
	8	.\" distribution and use acknowledge that the software was developed
	9	.\" by the University of California, Berkeley. The name of the
	10	.\" University may not be used to endorse or promote products derived
	11	.\" from this software without specific prior written permission.
	12	.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
	13	.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
	14	.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
	15	.\"
	16	.\" @(#)fcntl.2 6.5 (Berkeley) %G%
c24fefdc	17	.\"
4ef918f1	18	.TH FCNTL 2 ""
c24fefdc KM	19	.UC 5
	20	.SH NAME
	21	fcntl \- file control
	22	.SH SYNOPSIS
	23	.nf
	24	.ft B
	25	#include <fcntl.h>
	26	.PP
	27	.ft B
	28	res = fcntl(fd, cmd, arg)
	29	int res;
	30	int fd, cmd, arg;
	31	.ft R
	32	.SH DESCRIPTION
	33	.I Fcntl
	34	provides for control over descriptors.
	35	The argument
	36	.I fd
	37	is a descriptor to be operated on by
	38	.I cmd
	39	as follows:
	40	.TP 15
	41	F_DUPFD
	42	Return a new descriptor as follows:
	43	.IP
	44	Lowest numbered available descriptor greater than or equal to
	45	.I arg.
	46	.IP
	47	Same object references as the original descriptor.
	48	.IP
	49	New descriptor shares the same file pointer if the object
	50	was a file.
	51	.IP
	52	Same access mode (read, write or read/write).
	53	.IP
	54	Same file status flags (i.e., both file descriptors
	55	share the same file status flags).
	56	.IP
	57	The close-on-exec flag associated with the new file descriptor
	58	is set to remain open across
	59	.IR execv (2)
	60	system calls.
	61	.TP 15
	62	F_GETFD
	63	Get the close-on-exec flag associated with the file descriptor
	64	.IR fd .
	65	If the low-order bit is 0, the file will remain open across
	66	.IR exec ,
	67	otherwise the file will be closed upon execution of
	68	.I exec.
	69	.TP 15
	70	F_SETFD
	71	Set the close-on-exec flag associated with
	72	.I fd
	73	to the low order bit of
	74	.I arg
	75	(0 or 1 as above).
	76	.TP 15
	77	F_GETFL
	78	Get descriptor status flags, as described below.
	79	.TP 15
	80	F_SETFL
	81	Set descriptor status flags.
	82	.TP 15
83	F_GETOWN
84	Get the process ID or process group
85	currently receiving SIGIO and SIGURG
86	signals; process groups are returned
87	as negative values.
88	.TP
89	F_SETOWN
90	Set the process or process group
91	to receive SIGIO and SIGURG signals;
92	process groups are specified by supplying
93	.I arg
94	as negative, otherwise
95	.I arg
96	is interpreted as a process ID.
97	.LP
98	The flags for the F_GETFL and F_SETFL flags are as follows:
99	.TP 15
100	FNDELAY
101	Non-blocking I/O; if no data is available to a
102	.I read
103	call, or if a write operation would block,
104	the call returns -1 with the error EWOULDBLOCK.
105	.TP
106	FAPPEND
107	Force each write to append at the end of file;
108	corresponds to the O_APPEND flag of
109	.IR open (2).
110	.TP
111	FASYNC
112	Enable the SIGIO signal to be sent to the process group
d4bad45b	113	when I/O is possible, e.g.,
c24fefdc KM	114	upon availability of data to be read.
	115	.SH "RETURN VALUE
	116	Upon successful completion, the value returned depends on
	117	.I cmd
	118	as follows:
	119	.sp .5v
	120	.nf
	121	.ta .25i 1.25i
	122	F_DUPFD A new file descriptor.
	123	F_GETFD Value of flag (only the low-order bit is defined).
	124	F_GETFL Value of flags.
	125	F_GETOWN Value of file descriptor owner.
	126	other Value other than \-1.
	127	.fi
	128	.sp .5v
	129	Otherwise, a value of \-1 is returned and
	130	.I errno
	131	is set to indicate the error.
	132	.SH ERRORS
	133	.I Fcntl
	134	will fail if one or more of the following are true:
	135	.TP 15
	136	[EBADF]
	137	.I Fildes
	138	is not a valid open file descriptor.
	139	.TP 15
	140	[EMFILE]
	141	.I Cmd
	142	is F_DUPFD and the maximum allowed number of file descriptors are currently
	143	open.
	144	.TP 15
	145	[EINVAL]
	146	.I Cmd
	147	is F_DUPFD and
	148	.I arg
d4bad45b	149	is negative or greater than the maximum allowable number
c24fefdc KM	150	(see
c24fefdc KM	151	.IR getdtablesize (2)).
cae3bf24 MK	152	.TP 15
	153	[ESRCH]
	154	.I Cmd
	155	is F_SETOWN and
	156	the process ID given as argument is not in use.
c24fefdc KM	157	.SH "SEE ALSO
	158	close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
	159	.SH BUGS
	160	The asynchronous I/O facilities of FNDELAY and FASYNC
1df601cf	161	are currently available only for tty and socket operations.