openat — open a file relative to a directory file descriptor
#define _ATFILE_SOURCE #include <fcntl.h>
int
openat( |
int | dirfd, |
| const char * | pathname, | |
| int | flags); |
int
openat( |
int | dirfd, |
| const char * | pathname, | |
| int | flags, | |
| mode_t | mode); |
The openat() system call
operates in exactly the same way as open(2), except for the
differences described in this manual page.
If the pathname given in pathname is relative, then it
is interpreted relative to the directory referred to by the
file descriptor dirfd
(rather than relative to the current working directory of the
calling process, as is done by open(2) for a relative
pathname).
If pathname is
relative and dirfd is
the special value AT_FDCWD,
then pathname is
interpreted relative to the current working directory of the
calling process (like open(2)).
If pathname is
absolute, then dirfd
is ignored.
On success, openat() returns
a new file descriptor. On error, −1 is returned and
errno is set to indicate the
error.
The same errors that occur for open(2) can also occur for
openat(). The following
additional errors can occur for openat():
dirfd is not
a valid file descriptor.
pathname is
relative and dirfd is a file
descriptor referring to a file other than a
directory.
This system call is non-standard but is proposed for inclusion in a future revision of POSIX.1. A similar system call exists on Solaris.
openat() and other similar
system calls suffixed "at" are supported for two reasons.
First, openat() allows an
application to avoid race conditions that could occur when
using open(2) to open files in
directories other than the current working directory. These
race conditions result from the fact that some component of
the directory prefix given to open(2) could be changed in
parallel with the call to open(2). Such races can be
avoided by opening a file descriptor for the target
directory, and then specifying that file descriptor as the
dirfd argument of
openat().
Second, openat() allows the
implementation of a per-thread "current working directory",
via file descriptor(s) maintained by the application. (This
functionality can also be obtained by tricks based on the use
of /proc/self/fd/, but less
efficiently.)dirfd
faccessat(2), fchmodat(2), fchownat(2), fstatat(2), futimesat(2), linkat(2), mkdirat(2), mknodat(2), open(2), readlinkat(2), renameat(2), symlinkat(2), unlinkat(2), mkfifoat(3), path_resolution(7)
This page is part of release 2.79 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man-pages/.
|
This manpage is Copyright (C) 2006, Michael Kerrisk Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |