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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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FDOPENDIR(3P) POSIX Programmer's Manual FDOPENDIR(3P)
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.
fdopendir, opendir — open directory associated with file descriptor
#include <dirent.h>
DIR *fdopendir(int fd);
DIR *opendir(const char *dirname);
The fdopendir() function shall be equivalent to the opendir()
function except that the directory is specified by a file descriptor
rather than by a name. The file offset associated with the file
descriptor at the time of the call determines which entries are
returned.
Upon successful return from fdopendir(), the file descriptor is under
the control of the system, and 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.
Upon calling closedir() the file descriptor shall be closed.
It is unspecified whether the FD_CLOEXEC flag will be set on the file
descriptor by a successful call to fdopendir().
The opendir() function shall open a directory stream corresponding to
the directory named by the dirname argument. The directory stream is
positioned at the first entry. If the type DIR is implemented using a
file descriptor, applications shall only be able to open up to a
total of {OPEN_MAX} files and directories.
If the type DIR is implemented using a file descriptor, the
descriptor shall be obtained as if the O_DIRECTORY flag was passed to
open().
Upon successful completion, these functions shall return a pointer to
an object of type DIR. Otherwise, these functions shall return a
null pointer and set errno to indicate the error.
The fdopendir() function shall fail if:
EBADF The fd argument is not a valid file descriptor open for
reading.
ENOTDIR
The descriptor fd is not associated with a directory.
The opendir() function shall fail if:
EACCES Search permission is denied for the component of the path
prefix of dirname or read permission is denied for dirname.
ELOOP A loop exists in symbolic links encountered during resolution
of the dirname argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of dirname does not name an existing directory or
dirname is an empty string.
ENOTDIR
A component of dirname names an existing file that is neither
a directory nor a symbolic link to a directory.
The opendir() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the dirname argument.
EMFILE All file descriptors available to the process are currently
open.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate result
with a length that exceeds {PATH_MAX}.
ENFILE Too many files are currently open in the system.
The following sections are informative.
Open a Directory Stream
The following program fragment demonstrates how the opendir()
function is used.
#include <dirent.h>
...
DIR *dir;
struct dirent *dp;
...
if ((dir = opendir (".")) == NULL) {
perror ("Cannot open .");
exit (1);
}
while ((dp = readdir (dir)) != NULL) {
...
Find And Open a File
The following program searches through a given directory looking for
files whose name does not begin with a dot and whose size is larger
than 1 MiB.
#include <stdio.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct stat statbuf;
DIR *d;
struct dirent *dp;
int dfd, ffd;
if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {
fprintf(stderr, "Cannot open ./tmp directory\n");
exit(1);
}
while ((dp = readdir(d)) != NULL) {
if (dp->d_name[0] == '.')
continue;
/* there is a possible race condition here as the file
* could be renamed between the readdir and the open */
if ((ffd = openat(dfd, dp->d_name, O_RDONLY)) == -1) {
perror(dp->d_name);
continue;
}
if (fstat(ffd, &statbuf) == 0 && statbuf.st_size > (1024*1024)) {
/* found it ... */
printf("%s: %jdK\n", dp->d_name,
(intmax_t)(statbuf.st_size / 1024));
}
close(ffd);
}
closedir(d); // note this implicitly closes dfd
return 0;
}
The opendir() function should be used in conjunction with readdir(),
closedir(), and rewinddir() to examine the contents of the directory
(see the EXAMPLES section in readdir(3p)). This method is
recommended for portability.
The purpose of the fdopendir() function is to enable opening files in
directories other than the current working directory without exposure
to race conditions. Any part of the path of a file could be changed
in parallel to a call to opendir(), resulting in unspecified
behavior.
Based on historical implementations, the rules about file descriptors
apply to directory streams as well. However, this volume of
POSIX.1‐2008 does not mandate that the directory stream be
implemented using file descriptors. The description of closedir()
clarifies that if a file descriptor is used for the directory stream,
it is mandatory that closedir() deallocate the file descriptor. When
a file descriptor is used to implement the directory stream, it
behaves as if the FD_CLOEXEC had been set for the file descriptor.
The directory entries for dot and dot-dot are optional. This volume
of POSIX.1‐2008 does not provide a way to test a priori for their
existence because an application that is portable must be written to
look for (and usually ignore) those entries. Writing code that
presumes that they are the first two entries does not always work, as
many implementations permit them to be other than the first two
entries, with a ``normal'' entry preceding them. There is negligible
value in providing a way to determine what the implementation does
because the code to deal with dot and dot-dot must be written in any
case and because such a flag would add to the list of those flags
(which has proven in itself to be objectionable) and might be abused.
Since the structure and buffer allocation, if any, for directory
operations are defined by the implementation, this volume of
POSIX.1‐2008 imposes no portability requirements for erroneous
program constructs, erroneous data, or the use of unspecified values
such as the use or referencing of a dirp value or a dirent structure
value after a directory stream has been closed or after a fork() or
one of the exec function calls.
None.
closedir(3p), dirfd(3p), fstatat(3p), open(3p), readdir(3p),
rewinddir(3p), symlink(3p)
The Base Definitions volume of POSIX.1‐2008, dirent.h(0p),
sys_types.h(0p)
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 FDOPENDIR(3P)
Pages that refer to this page: dirent.h(0p), closedir(3p), dirfd(3p), fstatat(3p), ftw(3p), glob(3p), nftw(3p), open(3p), opendir(3p), readdir(3p), rewinddir(3p), seekdir(3p), symlink(3p), telldir(3p)
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