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.TH FDOPENDIR "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

fdopendir, opendir

\(em open directory associated with file descriptor

.SH SYNOPSIS

.LP

.nf

#include <dirent.h>

.P

DIR *fdopendir(int \fIfd\fP);

DIR *opendir(const char *\fIdirname\fP);

.fi

.SH DESCRIPTION

The

\fIfdopendir\fR()

function shall be equivalent to the

\fIopendir\fR()

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.

.P

Upon successful return from

\fIfdopendir\fR(),

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

\fIclosedir\fR(),

\fIreaddir\fR(),

\fIreaddir_r\fR(),

\fIrewinddir\fR(),

or

\fIseekdir\fR(),

the behavior is undefined. Upon calling

\fIclosedir\fR()

the file descriptor shall be closed.

.P

It is unspecified whether the FD_CLOEXEC flag will be set on the file

descriptor by a successful call to

\fIfdopendir\fR().

.P

The

\fIopendir\fR()

function shall open a directory stream corresponding to the directory

named by the

.IR dirname

argument. The directory stream is positioned at the first entry. If

the type

.BR DIR

is implemented using a file descriptor, applications shall only be

able to open up to a total of

{OPEN_MAX}

files and directories.

.P

If the type

.BR DIR

is implemented using a file descriptor, the descriptor shall be

obtained as if the O_DIRECTORY flag was passed to

\fIopen\fR().

.SH "RETURN VALUE"

Upon successful completion, these functions shall return

a pointer to an object of type

.BR DIR .

Otherwise, these functions shall return a null pointer and set

.IR errno

to indicate the error.

.SH ERRORS

The

\fIfdopendir\fR()

function shall fail if:

.TP

.BR EBADF

The

.IR fd

argument is not a valid file descriptor open for reading.

.TP

.BR ENOTDIR

The descriptor

.IR fd

is not associated with a directory.

.P

The

\fIopendir\fR()

function shall fail if:

.TP

.BR EACCES

Search permission is denied for the component of the path prefix of

.IR dirname

or read permission is denied for

.IR dirname .

.TP

.BR ELOOP

A loop exists in symbolic links encountered during resolution of the

.IR dirname

argument.

.TP

.BR ENAMETOOLONG

.br

The length of a component of a pathname is longer than

{NAME_MAX}.

.TP

.BR ENOENT

A component of

.IR dirname

does not name an existing directory or

.IR dirname

is an empty string.

.TP

.BR ENOTDIR

A component of

.IR dirname

names an existing file that is neither a directory nor a symbolic link

to a directory.

.br

.P

The

\fIopendir\fR()

function may fail if:

.TP

.BR ELOOP

More than

{SYMLOOP_MAX}

symbolic links were encountered during resolution of the

.IR dirname

argument.

.TP

.BR EMFILE

All file descriptors available to the process are currently open.

.TP

.BR ENAMETOOLONG

.br

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}.

.TP

.BR ENFILE

Too many files are currently open in the system.

.LP

.IR "The following sections are informative."

.SH EXAMPLES

.SS "Open a Directory Stream"

.P

The following program fragment demonstrates how the

\fIopendir\fR()

function is used.

.sp

.RS 4

.nf

\fB

#include <dirent.h>

\&...

    DIR *dir;

    struct dirent *dp;

\&...

    if ((dir = opendir (".")) == NULL) {

        perror ("Cannot open .");

        exit (1);

    }

.P

    while ((dp = readdir (dir)) != NULL) {

\&...

.fi \fR

.P

.RE

.SS "Find And Open a File"

.P

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.

.sp

.RS 4

.nf

\fB

#include <stdio.h>

#include <dirent.h>

#include <fcntl.h>

#include <sys/stat.h>

#include <stdint.h>

#include <stdlib.h>

#include <unistd.h>

.P

int

main(int argc, char *argv[])

{

    struct stat statbuf;

    DIR *d;

    struct dirent *dp;

    int dfd, ffd;

.P

    if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {

        fprintf(stderr, "Cannot open ./tmp directory\en");

        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\en", dp->d_name,

                (intmax_t)(statbuf.st_size / 1024));

        }

        close(ffd);

    }

    closedir(d); // note this implicitly closes dfd

    return 0;

}

.fi \fR

.P

.RE

.SH "APPLICATION USAGE"

The

\fIopendir\fR()

function should be used in conjunction with

\fIreaddir\fR(),

\fIclosedir\fR(),

and

\fIrewinddir\fR()

to examine the contents of the directory (see the EXAMPLES section in

.IR "\fIreaddir\fR\^(\|)").

This method is recommended for portability.

.SH RATIONALE

The purpose of the

\fIfdopendir\fR()

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

\fIopendir\fR(),

resulting in unspecified behavior.

.P

Based on historical implementations, the rules about file descriptors

apply to directory streams as well. However, this volume of POSIX.1\(hy2008 does not

mandate that the directory stream be implemented using file

descriptors. The description of

\fIclosedir\fR()

clarifies that if a file descriptor is used for the directory stream,

it is mandatory that

\fIclosedir\fR()

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.

.P

The directory entries for dot

and dot-dot

are optional. This volume of POSIX.1\(hy2008 does not provide a way to test

.IR "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.

.P

Since the structure and buffer allocation, if any, for directory

operations are defined by the implementation, this volume of POSIX.1\(hy2008 imposes no

portability requirements for erroneous program constructs, erroneous

data, or the use of unspecified values such as the use or referencing

of a

.IR dirp

value or a

.BR dirent

structure value after a directory stream has been closed or after a

\fIfork\fR()

or one of the

.IR exec

function calls.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fIclosedir\fR\^(\|)",

.IR "\fIdirfd\fR\^(\|)",

.IR "\fIfstatat\fR\^(\|)",

.IR "\fIopen\fR\^(\|)",

.IR "\fIreaddir\fR\^(\|)",

.IR "\fIrewinddir\fR\^(\|)",

.IR "\fIsymlink\fR\^(\|)"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "\fB<dirent.h>\fP",

.IR "\fB<sys_types.h>\fP"

.SH COPYRIGHT

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 .