plucky (3) dirfd.3posix.gz

Provided by: manpages-posix-dev_2017a-2_all bug

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>


       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 .