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 man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .