Name
openat — open a file relative to a directory file
descriptor
Synopsis
int
openat( |
int |
dirfd, |
| |
const char * |
pathname, |
| |
int |
flags); |
int
openat( |
int |
dirfd, |
| |
const char * |
pathname, |
| |
int |
flags, |
| |
mode_t |
mode); |
DESCRIPTION
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.
RETURN VALUE
On success, openat() returns
a new file descriptor. On error, −1 is returned and
errno is set to indicate the
error.
ERRORS
The same errors that occur for open(2) can also occur for
openat(). The following
additional errors can occur for openat():
- EBADF
-
dirfd is not
a valid file descriptor.
- ENOTDIR
-
pathname is
relative and dirfd is a file
descriptor referring to a file other than a
directory.
VERSIONS
openat() was added to Linux
in kernel 2.6.16.
CONFORMING TO
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.
NOTES
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/dirfd, but less
efficiently.)
SEE ALSO
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 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.
|
