215 lines
5.9 KiB
Groff
215 lines
5.9 KiB
Groff
.\" $NetBSD: dirent.3,v 1.7 2021/08/12 20:25:26 andvar Exp $
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)dir.5 8.3 (Berkeley) 4/19/94
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.\"
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.Dd September 7, 2019
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.Dt DIRENT 3
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.Os
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.Sh NAME
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.Nm dirent
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.Nd directory format
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/dirent.h
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.Ft mode
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.Fn DTTOIF "dirtype"
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.Ft dirtype
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.Fn IFTODT "mode"
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.Sh DESCRIPTION
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Directories provide a convenient hierarchical method of grouping
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files while obscuring the underlying details of the storage medium.
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A directory file is differentiated from a plain file
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by a flag in its
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.Xr inode 5
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entry.
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It consists of records (directory entries) each of which contains
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information about a file and a pointer to the file itself.
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Directory entries may contain other directories
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as well as plain files; such nested directories are referred to as
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subdirectories.
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A hierarchy of directories and files is formed in this manner
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and is called a file system (or referred to as a file system tree).
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.\" An entry in this tree,
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.\" nested or not nested,
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.\" is a pathname.
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.Pp
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Each directory file contains two special directory entries; one is a pointer
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to the directory itself
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called dot
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.Ql \&.
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and the other a pointer to its parent directory called dot-dot
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.Ql \&.. .
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Dot and dot-dot
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are valid pathnames, however,
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the system root directory
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.Ql / ,
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has no parent and dot-dot points to itself like dot.
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.Pp
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File system nodes are ordinary directory files on which has
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been grafted a file system object, such as a physical disk or a
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partitioned area of such a disk.
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(See
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.Xr mount 8 . )
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.Sh IMPLEMENTATION NOTES
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The directory entry format is defined in the file
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.In sys/dirent.h ,
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which is also included by
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.In dirent.h .
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The format is represented by the
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.Em dirent
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structure, which contains the following entries:
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.Bd -literal -offset indent
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ino_t d_fileno;
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uint16_t d_reclen;
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uint16_t d_namlen;
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uint8_t d_type;
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char d_name[MAXNAMLEN + 1];
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.Ed
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.Pp
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These are:
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.Bl -enum -offset indent
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.It
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The
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.Fa d_fileno
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entry is a number which is unique for each
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distinct file in the filesystem.
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Files that are linked by hard links (see
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.Xr link 2 )
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have the same
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.Fa d_fileno .
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If
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.Fa d_fileno
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is zero, the entry refers to a deleted file.
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The type
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.Va ino_t
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is defined in
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.In sys/types.h .
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.It
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The
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.Fa d_reclen
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entry is the length, in bytes, of the directory record.
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.It
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The
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.Fa d_namlen
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entry specifies the length of the file name excluding the NUL.
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Thus the actual size of
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.Fa d_name
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may vary from 1 to
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.Dv MAXNAMLEN
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\&+ 1.
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.It
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The
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.Fa d_type
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is the type of the file.
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.It
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The
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.Fa d_name
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entry contains a NUL-terminated file name.
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.El
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.Pp
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The following table lists the types available for
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.Vt d_type
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and the corresponding ones used in the
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.Em struct stat
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(see
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.Xr stat 2 ) ,
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respectively:
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.Pp
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.Bl -column -offset indent -compact \
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"DT_UNKNOWN " "DT_UNKNOWN " "DT_UNKNOWN "
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.It Sy Dirent Ta Sy Stat Ta Sy Description
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.It Dv DT_UNKNOWN Ta - Ta unknown file type
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.It Dv DT_FIFO Ta Dv S_IFIFO Ta named pipe
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.It Dv DT_CHR Ta Dv S_IFCHR Ta character device
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.It Dv DT_DIR Ta Dv S_IFDIR Ta directory
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.It Dv DT_BLK Ta Dv S_IFBLK Ta block device
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.It Dv DT_REG Ta Dv S_IFREG Ta regular file
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.It Dv DT_LNK Ta Dv S_IFLNK Ta symbolic link
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.It Dv DT_SOCK Ta Dv S_IFSOCK Ta UNIX domain socket
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.It Dv DT_WHT Ta Dv S_IFWHT Ta dummy Dq whiteout inode
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.El
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.Pp
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The
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.Dv DT_WHT
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type is internal to the implementation and
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should not be seen in normal user applications.
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The macros
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.Fn DTTOIF
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and
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.Fn IFTODT
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can be used to convert from
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.Em struct dirent
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types to
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.Em struct stat
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types, and vice versa.
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.Sh COMPATIBILITY
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The
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.St -p1003.1-2001
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standard specifies only the fields
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.Va d_ino
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and
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.Va d_name .
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The remaining fields are available on many, but not all systems.
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.Pp
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Furthermore, the standard leaves the size of
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.Va d_name
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as unspecified, mentioning only that the number of
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bytes preceding the terminating NUL shall not exceed
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.Dv NAME_MAX .
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Because of this, and because the
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.Va d_namlen
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field may not be present, a portable application should determine the size of
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.Va d_name
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by using
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.Xr strlen 3
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instead of applying the
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.Fn sizeof
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operator.
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.Sh SEE ALSO
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.Xr getdents 2 ,
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.Xr fs 5 ,
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.Xr inode 5
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.\" .Sh STANDARDS
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.\"
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.\" XXX: Conformance is unclear, cf. PR lib/43310.
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.\"
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.\" Given the noted limitations, the
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.\".In dirent.h
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.\" header conforms to
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.\" .St -p1003.1-2001 .
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.Sh HISTORY
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A
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directory file format appeared in
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.At v1 .
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The
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.Em dirent
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structure appeared in
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.Bx 4.3 reno .
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