Section (2) readdir
Name
readdir — read directory entry
Synopsis
int
readdir( |
unsigned int fd, |
struct old_linux_dirent *dirp, | |
unsigned int count) ; |
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Note |
---|---|
There is no glibc wrapper for this system call; see NOTES. |
DESCRIPTION
This is not the function you are interested in. Look at readdir(3) for the POSIX conforming C library interface. This page documents the bare kernel system call interface, which is superseded by getdents(2).
readdir
() reads one
old_linux_dirent structure
from the directory referred to by the file descriptor
fd
into the buffer
pointed to by dirp
.
The argument count
is
ignored; at most one old_linux_dirent structure is read.
The old_linux_dirent
structure is declared (privately in Linux kernel file
fs/readdir.c
) as follows:
struct old_linux_dirent { unsigned long d_ino
; /* inode number */unsigned long d_offset
; /* offset to this old_linux_dirent */unsigned short d_namlen
; /* length of this d_name */char d_name
[1]; /* filename (null-terminated) */};
d_ino
is an inode
number. d_offset
is
the distance from the start of the directory to this
old_linux_dirent. d_reclen
is the size of
d_name
, not counting
the terminating null byte (_zsingle_quotesz_ _zsingle_quotesz_). d_name
is a null-terminated
filename.
RETURN VALUE
On success, 1 is returned. On end of directory, 0 is
returned. On error, −1 is returned, and errno
is set appropriately.
ERRORS
- EBADF
-
Invalid file descriptor
fd
. - EFAULT
-
Argument points outside the calling process_zsingle_quotesz_s address space.
- EINVAL
-
Result buffer is too small.
- ENOENT
-
No such directory.
- ENOTDIR
-
File descriptor does not refer to a directory.
NOTES
Glibc does not provide a wrapper for this system call; call it using syscall(2). You will need to define the old_linux_dirent structure yourself. However, probably you should use readdir(3) instead.
This system call does not exist on x86-64.
COLOPHON
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (C) 1995 Andries Brouwer (aebcwi.nl) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END Written 11 June 1995 by Andries Brouwer <aebcwi.nl> Modified 22 July 1995 by Michael Chastain <mecduracef.shout.net>: In 1.3.X, returns only one entry each time; return value is different. Modified 2004-12-01, mtk, fixed headers listed in SYNOPSIS |
Section (3) readdir
Name
readdir — read a directory
Synopsis
#include <dirent.h>
struct dirent
*readdir( |
DIR *dirp) ; |
DESCRIPTION
The readdir
() function
returns a pointer to a dirent
structure representing the next directory entry in the
directory stream pointed to by dirp
. It returns NULL on
reaching the end of the directory stream or if an error
occurred.
In the glibc implementation, the dirent structure is defined as follows:
struct dirent { ino_t d_ino
; /* Inode number */off_t d_off
; /* Not an offset; see below */unsigned short d_reclen
; /* Length of this record */unsigned char d_type
; /* Type of file; not supported
by all filesystem types */char d_name
[256]; /* Null-terminated filename */};
The only fields in the dirent structure that are mandated by
POSIX.1 are d_name
and d_ino
. The other
fields are unstandardized, and not present on all systems;
see NOTES below for some further details.
The fields of the dirent structure are as follows:
d_ino
-
This is the inode number of the file.
d_off
-
The value returned in
d_off
is the same as would be returned by calling telldir(3) at the current position in the directory stream. Be aware that despite its type and name, thed_off
field is seldom any kind of directory offset on modern filesystems. Applications should treat this field as an opaque value, making no assumptions about its contents; see also telldir(3). d_reclen
-
This is the size (in bytes) of the returned record. This may not match the size of the structure definition shown above; see NOTES.
d_type
-
This field contains a value indicating the file type, making it possible to avoid the expense of calling lstat(2) if further actions depend on the type of the file.
When a suitable feature test macro is defined (
_DEFAULT_SOURCE
on glibc versions since 2.19, or_BSD_SOURCE
on glibc versions 2.19 and earlier), glibc defines the following macro constants for the value returned ind_type
:DT_BLK
-
This is a block device.
DT_CHR
-
This is a character device.
DT_DIR
-
This is a directory.
DT_FIFO
-
This is a named pipe (FIFO).
DT_LNK
-
This is a symbolic link.
DT_REG
-
This is a regular file.
DT_SOCK
-
This is a UNIX domain socket.
DT_UNKNOWN
-
The file type could not be determined.
Currently, only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full support for returning the file type in
d_type
. All applications must properly handle a return ofDT_UNKNOWN
. d_name
-
This field contains the null terminated filename. See NOTES.
The data returned by readdir
() may be overwritten by subsequent
calls to readdir
() for the same
directory stream.
RETURN VALUE
On success, readdir
()
returns a pointer to a dirent
structure. (This structure may be statically allocated; do
not attempt to free(3) it.)
If the end of the directory stream is reached, NULL is
returned and errno
is not
changed. If an error occurs, NULL is returned and
errno
is set appropriately. To
distinguish end of stream and from an error, set errno
to zero before calling readdir
() and then check the value of
errno
if NULL is returned.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
readdir () |
Thread safety | MT-Unsafe race:dirstream |
In the current POSIX.1 specification (POSIX.1-2008),
readdir
() is not required to be
thread-safe. However, in modern implementations (including
the glibc implementation), concurrent calls to readdir
() that specify different directory
streams are thread-safe. In cases where multiple threads must
read from the same directory stream, using readdir
() with external synchronization is
still preferable to the use of the deprecated readdir_r(3) function. It
is expected that a future version of POSIX.1 will require
that readdir
() be thread-safe
when concurrently employed on different directory
streams.
NOTES
A directory stream is opened using opendir(3).
The order in which filenames are read by successive calls
to readdir
() depends on the
filesystem implementation; it is unlikely that the names will
be sorted in any fashion.
Only the fields d_name
and (as an XSI
extension) d_ino
are
specified in POSIX.1. Other than Linux, the d_type
field is available
mainly only on BSD systems. The remaining fields are
available on many, but not all systems. Under glibc, programs
can check for the availability of the fields not defined in
POSIX.1 by testing whether the macros _DIRENT_HAVE_D_NAMLEN
, _DIRENT_HAVE_D_RECLEN
, _DIRENT_HAVE_D_OFF
, or _DIRENT_HAVE_D_TYPE
are defined.
The d_name field
The dirent structure
definition shown above is taken from the glibc headers, and
shows the d_name
field with a fixed size.
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Warning |
---|---|
applications should avoid any dependence on the
size of the |
POSIX.1 explicitly notes that this field should not be
used as an lvalue. The standard also notes that the use of
sizeof(d_name)
is
incorrect; use strlen(d_name)
instead. (On
some systems, this field is defined as char d_name[1]!) By implication,
the use sizeof(struct
dirent) to capture the size of the record
including the size of d_name
is also incorrect.
Note that while the call
fpathconf(fd, _PC_NAME_MAX)
returns the value 255 for most filesystems, on some
filesystems (e.g., CIFS, Windows SMB servers), the
null-terminated filename that is (correctly) returned in
d_name
can actually
exceed this size. In such cases, the d_reclen
field will contain a
value that exceeds the size of the glibc dirent structure shown above.
SEE ALSO
getdents(2), read(2), closedir(3), dirfd(3), ftw(3), offsetof(3), opendir(3), readdir_r(3), rewinddir(3), scandir(3), seekdir(3), telldir(3)
COLOPHON
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (C) 1993 David Metcalfe (davidprism.demon.co.uk) and Copyright (C) 2008, 2016 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Linux libc source code Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_Reilly & Associates, 1991) 386BSD man pages Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faithcs.unc.edu) Modified 11 June 1995 by Andries Brouwer (aebcwi.nl) Modified 22 July 1996 by Andries Brouwer (aebcwi.nl) 2007-07-30 Ulrich Drepper <drepperredhat.com>, mtk: Rework discussion of nonstandard structure fields. |