dirfd(3p) — Linux manual page


DIRFD(3P)                 POSIX Programmer's Manual                DIRFD(3P)

PROLOG         top

       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         top

       dirfd — extract the file descriptor used by a DIR stream

SYNOPSIS         top

       #include <dirent.h>

       int dirfd(DIR *dirp);

DESCRIPTION         top

       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         top

       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         top

       The dirfd() function may fail if:

       EINVAL The dirp argument does not refer to a valid directory stream.

              The implementation does not support the association of a file
              descriptor with a directory.

       The following sections are informative.

EXAMPLES         top



       The dirfd() function is intended to be a mechanism by which an
       application may obtain a file descriptor to use for the fchdir()

RATIONALE         top

       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().



SEE ALSO         top

       closedir(3p), fchdir(3p), fdopendir(3p), fileno(3p), open(3p),

       The Base Definitions volume of POSIX.1‐2008, dirent.h(0p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                           DIRFD(3P)

Pages that refer to this page: dirent.h(0p)closedir(3p)fchdir(3p)fdopendir(3p)fileno(3p)open(3p)readdir(3p)readdir_r(3p)