DIRFD(3P) POSIX Programmer's Manual DIRFD(3P)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.
NAMEdirfd — 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 inte‐
ger which contains a file descriptor for the stream pointed to by dirp.
Otherwise, it shall return −1 and may 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.
ENOTSUP
The implementation does not support the association of a file
descriptor with a directory.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The dirfd() function is intended to be a mechanism by which an applica‐
tion may obtain a file descriptor to use for the fchdir() function.
RATIONALE
This interface was introduced because the Base Definitions volume of
POSIX.1‐2008 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().
An implementation that does not support file descriptors referring to
directories may fail with [ENOTSUP].
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 ALSOclosedir(), fchdir(), fdopendir(), fileno(), open(), readdir()
The Base Definitions volume of POSIX.1‐2008, <dirent.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 DIRFD(3P)
