1FDOPENDIR(3P) POSIX Programmer's Manual FDOPENDIR(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 fdopendir, opendir — open directory associated with file descriptor
14
16 #include <dirent.h>
17 DIR *fdopendir(int fd);
19 DIR *opendir(const char *dirname);
20
22 The fdopendir() function shall be equivalent to the opendir() function
23 except that the directory is specified by a file descriptor rather than
24 by a name. The file offset associated with the file descriptor at the
25 time of the call determines which entries are returned.
26 Upon successful return from fdopendir(), the file descriptor is under
28 the control of the system, and if any attempt is made to close the file
29 descriptor, or to modify the state of the associated description, other
30 than by means of closedir(), readdir(), readdir_r(), rewinddir(), or
31 seekdir(), the behavior is undefined. Upon calling closedir() the file
32 descriptor shall be closed.
33 It is unspecified whether the FD_CLOEXEC flag will be set on the file
35 descriptor by a successful call to fdopendir().
36 The opendir() function shall open a directory stream corresponding to
38 the directory named by the dirname argument. The directory stream is
39 positioned at the first entry. If the type DIR is implemented using a
40 file descriptor, applications shall only be able to open up to a total
41 of {OPEN_MAX} files and directories.
42 If the type DIR is implemented using a file descriptor, the descriptor
44 shall be obtained as if the O_DIRECTORY flag was passed to open().
45
47 Upon successful completion, these functions shall return a pointer to
48 an object of type DIR. Otherwise, these functions shall return a null
49 pointer and set errno to indicate the error.
50
52 The fdopendir() function shall fail if:
53 EBADF The fd argument is not a valid file descriptor open for reading.
55 ENOTDIR
57 The descriptor fd is not associated with a directory.
58 The opendir() function shall fail if:
60 EACCES Search permission is denied for the component of the path prefix
62 of dirname or read permission is denied for dirname.
63 ELOOP A loop exists in symbolic links encountered during resolution of
65 the dirname argument.
66 ENAMETOOLONG
68 The length of a component of a pathname is longer than
69 {NAME_MAX}.
70 ENOENT A component of dirname does not name an existing directory or
72 dirname is an empty string.
73 ENOTDIR
75 A component of dirname names an existing file that is neither a
76 directory nor a symbolic link to a directory.
77 The opendir() function may fail if:
79 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
81 resolution of the dirname argument.
82 EMFILE All file descriptors available to the process are currently
84 open.
85 ENAMETOOLONG
87 The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
88 tion of a symbolic link produced an intermediate result with a
89 length that exceeds {PATH_MAX}.
90 ENFILE Too many files are currently open in the system.
92 The following sections are informative.
94
96 Open a Directory Stream
97 The following program fragment demonstrates how the opendir() function
98 is used.
99 #include <dirent.h>
101 ...
102 DIR *dir;
103 struct dirent *dp;
104 ...
105 if ((dir = opendir (".")) == NULL) {
106 perror ("Cannot open .");
107 exit (1);
108 }
109 while ((dp = readdir (dir)) != NULL) {
111 ...
112 Find And Open a File
114 The following program searches through a given directory looking for
115 files whose name does not begin with a dot and whose size is larger
116 than 1 MiB.
117 #include <stdio.h>
119 #include <dirent.h>
120 #include <fcntl.h>
121 #include <sys/stat.h>
122 #include <stdint.h>
123 #include <stdlib.h>
124 #include <unistd.h>
125 int
127 main(int argc, char *argv[])
128 {
129 struct stat statbuf;
130 DIR *d;
131 struct dirent *dp;
132 int dfd, ffd;
133 if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {
135 fprintf(stderr, "Cannot open ./tmp directory\n");
136 exit(1);
137 }
138 while ((dp = readdir(d)) != NULL) {
139 if (dp->d_name[0] == '.')
140 continue;
141 /* there is a possible race condition here as the file
142 * could be renamed between the readdir and the open */
143 if ((ffd = openat(dfd, dp->d_name, O_RDONLY)) == -1) {
144 perror(dp->d_name);
145 continue;
146 }
147 if (fstat(ffd, &statbuf) == 0 && statbuf.st_size > (1024*1024)) {
148 /* found it ... */
149 printf("%s: %jdK\n", dp->d_name,
150 (intmax_t)(statbuf.st_size / 1024));
151 }
152 close(ffd);
153 }
154 closedir(d); // note this implicitly closes dfd
155 return 0;
156 }
157
159 The opendir() function should be used in conjunction with readdir(),
160 closedir(), and rewinddir() to examine the contents of the directory
161 (see the EXAMPLES section in readdir()). This method is recommended
162 for portability.
163
165 The purpose of the fdopendir() function is to enable opening files in
166 directories other than the current working directory without exposure
167 to race conditions. Any part of the path of a file could be changed in
168 parallel to a call to opendir(), resulting in unspecified behavior.
169 Based on historical implementations, the rules about file descriptors
171 apply to directory streams as well. However, this volume of
172 POSIX.1‐2008 does not mandate that the directory stream be implemented
173 using file descriptors. The description of closedir() clarifies that if
174 a file descriptor is used for the directory stream, it is mandatory
175 that closedir() deallocate the file descriptor. When a file descriptor
176 is used to implement the directory stream, it behaves as if the
177 FD_CLOEXEC had been set for the file descriptor.
178 The directory entries for dot and dot-dot are optional. This volume of
180 POSIX.1‐2008 does not provide a way to test a priori for their exis‐
181 tence because an application that is portable must be written to look
182 for (and usually ignore) those entries. Writing code that presumes that
183 they are the first two entries does not always work, as many implemen‐
184 tations permit them to be other than the first two entries, with a
185 ``normal'' entry preceding them. There is negligible value in providing
186 a way to determine what the implementation does because the code to
187 deal with dot and dot-dot must be written in any case and because such
188 a flag would add to the list of those flags (which has proven in itself
189 to be objectionable) and might be abused.
190 Since the structure and buffer allocation, if any, for directory opera‐
192 tions are defined by the implementation, this volume of POSIX.1‐2008
193 imposes no portability requirements for erroneous program constructs,
194 erroneous data, or the use of unspecified values such as the use or
195 referencing of a dirp value or a dirent structure value after a direc‐
196 tory stream has been closed or after a fork() or one of the exec func‐
197 tion calls.
198
200 None.
201
203 closedir(), dirfd(), fstatat(), open(), readdir(), rewinddir(), sym‐
204 link()
205 The Base Definitions volume of POSIX.1‐2008, <dirent.h>, <sys_types.h>
207
209 Portions of this text are reprinted and reproduced in electronic form
210 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
211 -- Portable Operating System Interface (POSIX), The Open Group Base
212 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
213 cal and Electronics Engineers, Inc and The Open Group. (This is
214 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
215 event of any discrepancy between this version and the original IEEE and
216 The Open Group Standard, the original IEEE and The Open Group Standard
217 is the referee document. The original Standard can be obtained online
218 at http://www.unix.org/online.html .
219 Any typographical or formatting errors that appear in this page are
221 most likely to have been introduced during the conversion of the source
222 files to man page format. To report such errors, see https://www.ker‐
223 nel.org/doc/man-pages/reporting_bugs.html .
224IEEE/The Open Group 2013 FDOPENDIR(3P)