DIRFD
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
dirfd
--- extract the file descriptor used by a DIR stream
SYNOPSIS
#include <dirent.h>
int dirfd(DIR *dirp);
DESCRIPTION
The
dirfd()
function shall return a file descriptor referring to the same directory
as the
dirp
argument. This file descriptor shall be closed by a call to
closedir().
If any attempt is made to close the file descriptor, or to modify the
state of the associated description, other than by means of
closedir(),
readdir(),
readdir_r(),
rewinddir(),
or
seekdir(),
the behavior is undefined.
RETURN VALUE
Upon successful completion, the
dirfd()
function shall return an integer which contains a file descriptor for
the stream pointed to by
dirp.
Otherwise, it shall return -1 and shall set
errno
to indicate the error.
ERRORS
The
dirfd()
function may fail if:
- EINVAL
-
The
dirp
argument does not refer to a valid directory stream.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The
dirfd()
function is intended to be a mechanism by which an application may
obtain a file descriptor to use for the
fchdir()
function.
RATIONALE
This interface was introduced because the Base Definitions volume of POSIX.1-2017 does not make public
the
DIR
data structure. Applications tend to use the
fchdir()
function on the file descriptor returned by this interface, and this
has proven useful for security reasons; in particular, it is a better
technique than others where directory names might change.
The description uses the term ``a file descriptor'' rather than ``the
file descriptor''. The implication intended is that an implementation
that does not use an
fd
for
opendir()
could still
open()
the directory to implement the
dirfd()
function. Such a descriptor must be closed later during a call to
closedir().
If it is necessary to allocate an
fd
to be returned by
dirfd(),
it should be done at the time of a call to
opendir().
FUTURE DIRECTIONS
None.
SEE ALSO
closedir(),
fchdir(),
fdopendir(),
fileno(),
open(),
readdir()
The Base Definitions volume of POSIX.1-2017,
<dirent.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .