1DIRFD(3P) POSIX Programmer's Manual DIRFD(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 dirfd — extract the file descriptor used by a DIR stream
14
16 #include <dirent.h>
17 int dirfd(DIR *dirp);
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21 The dirfd() function shall return a file descriptor referring to the
22 same directory as the dirp argument. This file descriptor shall be
23 closed by a call to closedir(). If any attempt is made to close the
24 file descriptor, or to modify the state of the associated description,
25 other than by means of closedir(), readdir(), readdir_r(), rewinddir(),
26 or seekdir(), the behavior is undefined.
27
29 Upon successful completion, the dirfd() function shall return an inte‐
30 ger which contains a file descriptor for the stream pointed to by dirp.
31 Otherwise, it shall return −1 and may set errno to indicate the error.
32
34 The dirfd() function may fail if:
35 EINVAL The dirp argument does not refer to a valid directory stream.
37 ENOTSUP
39 The implementation does not support the association of a file
40 descriptor with a directory.
41 The following sections are informative.
43
45 None.
46
48 The dirfd() function is intended to be a mechanism by which an applica‐
49 tion may obtain a file descriptor to use for the fchdir() function.
50
52 This interface was introduced because the Base Definitions volume of
53 POSIX.1‐2008 does not make public the DIR data structure. Applications
54 tend to use the fchdir() function on the file descriptor returned by
55 this interface, and this has proven useful for security reasons; in
56 particular, it is a better technique than others where directory names
57 might change.
58 The description uses the term ``a file descriptor'' rather than ``the
60 file descriptor''. The implication intended is that an implementation
61 that does not use an fd for opendir() could still open() the directory
62 to implement the dirfd() function. Such a descriptor must be closed
63 later during a call to closedir().
64 An implementation that does not support file descriptors referring to
66 directories may fail with [ENOTSUP].
67 If it is necessary to allocate an fd to be returned by dirfd(), it
69 should be done at the time of a call to opendir().
70
72 None.
73
75 closedir(), fchdir(), fdopendir(), fileno(), open(), readdir()
76 The Base Definitions volume of POSIX.1‐2008, <dirent.h>
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80 Portions of this text are reprinted and reproduced in electronic form
81 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
82 -- Portable Operating System Interface (POSIX), The Open Group Base
83 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
84 cal and Electronics Engineers, Inc and The Open Group. (This is
85 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
86 event of any discrepancy between this version and the original IEEE and
87 The Open Group Standard, the original IEEE and The Open Group Standard
88 is the referee document. The original Standard can be obtained online
89 at http://www.unix.org/online.html .
90 Any typographical or formatting errors that appear in this page are
92 most likely to have been introduced during the conversion of the source
93 files to man page format. To report such errors, see https://www.ker‐
94 nel.org/doc/man-pages/reporting_bugs.html .
95IEEE/The Open Group 2013 DIRFD(3P)