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 .