[dragonfly.git] / lib / libc / sys / readlink.2

.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)readlink.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/sys/readlink.2,v 1.17 2008/04/16 13:03:12 kib Exp $
.\"
.Dd August 6, 2010
.Dt READLINK 2
.Os
.Sh NAME
.Nm readlink ,
.Nm readlinkat
.Nd read value of a symbolic link
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn readlink "const char *path" "char *buf" "int bufsiz"
.Ft ssize_t
.Fn readlinkat "int fd" "const char *restrict path" "char *restrict buf" "size_t bufsize"
.Sh DESCRIPTION
The
.Fn readlink
system call
places the contents of the symbolic link
.Fa path
in the buffer
.Fa buf ,
which has size
.Fa bufsiz .
The
.Fn readlink
system call does not append a
.Dv NUL
character to
.Fa buf .
.Pp
The
.Fn readlinkat
system call is equivalent to
.Fn readlink
except in the case where
.Fa path
specifies a relative path.
In this case the symbolic link whose content is read relative to the
directory associated with the file descriptor
.Fa fd
instead of the current working directory.
If
.Fn readlinkat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fn readlink .
.Sh RETURN VALUES
The calls return the count of characters placed in the buffer
if it succeeds, or a \-1 if an error occurs, placing the error
code in the global variable
.Va errno .
.Sh ERRORS
The
.Fn readlink
system call
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EINVAL
The named file is not a symbolic link.
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.It Bq Er EFAULT
The
.Fa buf
argument
extends outside the process's allocated address space.
.El
.Pp
In addition to the errors returned by the
.Fn readlink ,
the
.Fn readlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.El
.Sh SEE ALSO
.Xr lstat 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn readlinkat
system call follows The Open Group Extended API Set 2 specification.
.Sh HISTORY
The
.Fn readlink
system call appeared in
.Bx 4.2 .
The
.Fn readlinkat
system call appeared in
.Dx 2.7 .
Commit	Line	Data
984263bc MD	1	.\" Copyright (c) 1983, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" Redistribution and use in source and binary forms, with or without
	5	.\" modification, are permitted provided that the following conditions
	6	.\" are met:
	7	.\" 1. Redistributions of source code must retain the above copyright
	8	.\" notice, this list of conditions and the following disclaimer.
	9	.\" 2. Redistributions in binary form must reproduce the above copyright
	10	.\" notice, this list of conditions and the following disclaimer in the
	11	.\" documentation and/or other materials provided with the distribution.
984263bc MD	12	.\" 4. Neither the name of the University nor the names of its contributors
	13	.\" may be used to endorse or promote products derived from this software
	14	.\" without specific prior written permission.
	15	.\"
	16	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	17	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	18	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	19	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	20	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	21	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	22	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	23	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	24	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	25	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	26	.\" SUCH DAMAGE.
	27	.\"
	28	.\" @(#)readlink.2 8.1 (Berkeley) 6/4/93
6d98f93c	29	.\" $FreeBSD: src/lib/libc/sys/readlink.2,v 1.17 2008/04/16 13:03:12 kib Exp $
984263bc	30	.\"
6d98f93c	31	.Dd August 6, 2010
984263bc MD	32	.Dt READLINK 2
	33	.Os
	34	.Sh NAME
6d98f93c SW	35	.Nm readlink ,
6d98f93c SW	36	.Nm readlinkat
984263bc MD	37	.Nd read value of a symbolic link
	38	.Sh LIBRARY
	39	.Lb libc
	40	.Sh SYNOPSIS
	41	.In unistd.h
	42	.Ft int
	43	.Fn readlink "const char path" "char buf" "int bufsiz"
6d98f93c SW	44	.Ft ssize_t
6d98f93c SW	45	.Fn readlinkat "int fd" "const char restrict path" "char restrict buf" "size_t bufsize"
984263bc	46	.Sh DESCRIPTION
6d98f93c SW	47	The
	48	.Fn readlink
	49	system call
984263bc MD	50	places the contents of the symbolic link
	51	.Fa path
	52	in the buffer
	53	.Fa buf ,
	54	which has size
	55	.Fa bufsiz .
	56	The
	57	.Fn readlink
6d98f93c	58	system call does not append a
984263bc MD	59	.Dv NUL
	60	character to
	61	.Fa buf .
6d98f93c SW	62	.Pp
	63	The
	64	.Fn readlinkat
	65	system call is equivalent to
	66	.Fn readlink
	67	except in the case where
	68	.Fa path
	69	specifies a relative path.
	70	In this case the symbolic link whose content is read relative to the
	71	directory associated with the file descriptor
	72	.Fa fd
	73	instead of the current working directory.
	74	If
	75	.Fn readlinkat
	76	is passed the special value
	77	.Dv AT_FDCWD
	78	in the
	79	.Fa fd
	80	parameter, the current working directory is used and the behavior is
	81	identical to a call to
	82	.Fn readlink .
984263bc	83	.Sh RETURN VALUES
6d98f93c SW	84	The calls return the count of characters placed in the buffer
6d98f93c SW	85	if it succeeds, or a \-1 if an error occurs, placing the error
984263bc MD	86	code in the global variable
	87	.Va errno .
	88	.Sh ERRORS
6d98f93c SW	89	The
	90	.Fn readlink
	91	system call
984263bc MD	92	will fail if:
	93	.Bl -tag -width Er
	94	.It Bq Er ENOTDIR
	95	A component of the path prefix is not a directory.
	96	.It Bq Er ENAMETOOLONG
	97	A component of a pathname exceeded 255 characters,
	98	or an entire path name exceeded 1023 characters.
	99	.It Bq Er ENOENT
	100	The named file does not exist.
	101	.It Bq Er EACCES
	102	Search permission is denied for a component of the path prefix.
	103	.It Bq Er ELOOP
	104	Too many symbolic links were encountered in translating the pathname.
	105	.It Bq Er EINVAL
	106	The named file is not a symbolic link.
	107	.It Bq Er EIO
	108	An I/O error occurred while reading from the file system.
	109	.It Bq Er EFAULT
6d98f93c SW	110	The
	111	.Fa buf
	112	argument
984263bc MD	113	extends outside the process's allocated address space.
984263bc MD	114	.El
6d98f93c SW	115	.Pp
	116	In addition to the errors returned by the
	117	.Fn readlink ,
	118	the
	119	.Fn readlinkat
	120	may fail if:
	121	.Bl -tag -width Er
	122	.It Bq Er EBADF
	123	The
	124	.Fa path
	125	argument does not specify an absolute path and the
	126	.Fa fd
	127	argument is neither
	128	.Dv AT_FDCWD
	129	nor a valid file descriptor open for searching.
	130	.It Bq Er ENOTDIR
	131	The
	132	.Fa path
	133	argument is not an absolute path and
	134	.Fa fd
	135	is neither
	136	.Dv AT_FDCWD
	137	nor a file descriptor associated with a directory.
	138	.El
984263bc MD	139	.Sh SEE ALSO
	140	.Xr lstat 2 ,
	141	.Xr stat 2 ,
	142	.Xr symlink 2 ,
	143	.Xr symlink 7
6d98f93c SW	144	.Sh STANDARDS
	145	The
	146	.Fn readlinkat
	147	system call follows The Open Group Extended API Set 2 specification.
984263bc MD	148	.Sh HISTORY
	149	The
	150	.Fn readlink
6d98f93c	151	system call appeared in
984263bc	152	.Bx 4.2 .
6d98f93c SW	153	The
	154	.Fn readlinkat
	155	system call appeared in
	156	.Dx 2.7 .