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 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 application may obtain a  file  descriptor
       to use for the fchdir() function.

RATIONALE

       This  interface  was  introduced because the Base Definitions volume of POSIX.1‐2008 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 ALSO

       closedir(), 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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .