dirfd(3p) — Linux manual page

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

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

       The Base Definitions volume of POSIX.1‐2017, dirent.h(0p)

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 .

IEEE/The Open Group               2017                         DIRFD(3P)

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

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