NAME
openat - open a file relative to a directory file descriptor
SYNOPSIS
#define _ATFILE_SOURCE
#include <fcntl.h>
I int openat(int dirfd , const char * pathname , int flags );
I int openat(int dirfd , const char * pathname , int flags \
", mode_t " mode );
DESCRIPTION
The
R 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
R 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
R AT_FDCWD ,
then
pathname
is interpreted relative to the current working
directory of the calling process (like
open(2)).
If
R pathname
is absolute, then
dirfd
is ignored.
RETURN VALUE
On success,
R 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
R openat ().
The following additional errors can occur for
R 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
R 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
R openat ()
and other similar system calls suffixed "at" are supported
for two reasons.
First,
R 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
R openat ().
Second,
R 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
R /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)
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