1c4ca77890
The d_off field has been added to the dirent structure recently. Currently filesystems don't support this feature. Support has been added and tested for zfs, ufs, ext2fs, fdescfs, msdosfs and unionfs. A stub implementation is available for cd9660, nandfs, udf and pseudofs but hasn't been tested. Motivation for this feature: our usecase is for a userspace nfs server (nfs-ganesha) with zfs. At the moment we cache direntry offsets by calling lseek once per entry, with this patch we can get the offset directly from getdirentries(2) calls which provides a significant speedup. Submitted by: Jack Halford <jack@gandi.net> Reviewed by: mckusick, pfg, rmacklem (previous versions) Sponsored by: Gandi.net MFC after: 1 week Differential revision: https://reviews.freebsd.org/D17917
168 lines
5.7 KiB
Groff
168 lines
5.7 KiB
Groff
.\" 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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.\" $FreeBSD$
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.\"
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.Dd November 14, 2018
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.Dt DIR 5
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.Os
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.Sh NAME
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.Nm dir ,
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.Nm dirent
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.Nd directory file format
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.Sh SYNOPSIS
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.In dirent.h
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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 2
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and
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.Xr mount 8 . )
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.Pp
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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 should not be included directly by applications):
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.Bd -literal
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#ifndef _SYS_DIRENT_H_
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#define _SYS_DIRENT_H_
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#include <machine/ansi.h>
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/*
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* The dirent structure defines the format of directory entries returned by
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* the getdirentries(2) system call.
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*
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* A directory entry has a struct dirent at the front of it, containing its
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* inode number, the length of the entry, and the length of the name
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* contained in the entry. These are followed by the name padded to a 8
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* byte boundary with null bytes. All names are guaranteed null terminated.
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* The maximum length of a name in a directory is MAXNAMLEN.
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* Explicit pad is added between the last member of the header and
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* d_name, to avoid having the ABI padding in the end of dirent on
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* LP64 arches. There is code depending on d_name being last. Also,
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* keeping this pad for ILP32 architectures simplifies compat32 layer.
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*/
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struct dirent {
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ino_t d_fileno; /* file number of entry */
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off_t d_off; /* directory offset of the next entry */
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__uint16_t d_reclen; /* length of this record */
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__uint8_t d_type; /* file type, see below */
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__uint8_t d_namlen; /* length of string in d_name */
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__uint32_t d_pad0;
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#if __BSD_VISIBLE
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#define MAXNAMLEN 255
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char d_name[MAXNAMLEN + 1]; /* name must be no longer than this */
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#else
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char d_name[255 + 1]; /* name must be no longer than this */
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#endif
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};
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/*
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* File types
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*/
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#define DT_UNKNOWN 0
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#define DT_FIFO 1
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#define DT_CHR 2
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#define DT_DIR 4
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#define DT_BLK 6
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#define DT_REG 8
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#define DT_LNK 10
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#define DT_SOCK 12
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#define DT_WHT 14
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/*
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* Convert between stat structure types and directory types.
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*/
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#define IFTODT(mode) (((mode) & 0170000) >> 12)
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#define DTTOIF(dirtype) ((dirtype) << 12)
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/*
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* The _GENERIC_DIRSIZ macro gives the minimum record length which will hold
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* the directory entry. This returns the amount of space in struct direct
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* without the d_name field, plus enough space for the name with a terminating
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* null byte (dp->d_namlen+1), rounded up to a 8 byte boundary.
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*
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* XXX although this macro is in the implementation namespace, it requires
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* a manifest constant that is not.
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*/
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#define _GENERIC_DIRLEN(namlen) \
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((__offsetof(struct dirent, d_name) + (namlen) + 1 + 7) & ~7)
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#define _GENERIC_DIRSIZ(dp) _GENERIC_DIRLEN((dp)->d_namlen)
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#endif /* __BSD_VISIBLE */
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#ifdef _KERNEL
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#define GENERIC_DIRSIZ(dp) _GENERIC_DIRSIZ(dp)
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#endif
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#endif /* !_SYS_DIRENT_H_ */
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.Ed
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.Sh SEE ALSO
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.Xr fs 5 ,
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.Xr inode 5
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.Sh HISTORY
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A
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.Nm
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file format appeared in
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.At v7 .
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.Sh BUGS
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The usage of the member d_type of struct dirent is unportable as it is
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.Fx Ns -specific .
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It also may fail on certain file systems, for example the cd9660 file system.
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