fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
309 lines
7.1 KiB
Groff
309 lines
7.1 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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.\" @(#)directory.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd August 31, 2016
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.Dt DIRECTORY 3
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.Os
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.Sh NAME
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.Nm opendir ,
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.Nm fdopendir ,
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.Nm readdir ,
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.Nm readdir_r ,
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.Nm telldir ,
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.Nm seekdir ,
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.Nm rewinddir ,
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.Nm closedir ,
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.Nm fdclosedir ,
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.Nm dirfd
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.Nd directory operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In dirent.h
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.Ft DIR *
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.Fn opendir "const char *filename"
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.Ft DIR *
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.Fn fdopendir "int fd"
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.Ft struct dirent *
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.Fn readdir "DIR *dirp"
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.Ft int
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.Fn readdir_r "DIR *dirp" "struct dirent *entry" "struct dirent **result"
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.Ft long
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.Fn telldir "DIR *dirp"
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.Ft void
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.Fn seekdir "DIR *dirp" "long loc"
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.Ft void
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.Fn rewinddir "DIR *dirp"
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.Ft int
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.Fn closedir "DIR *dirp"
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.Ft int
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.Fn fdclosedir "DIR *dirp"
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.Ft int
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.Fn dirfd "DIR *dirp"
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.Sh DESCRIPTION
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.Bf -symbolic
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The
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.Fn readdir_r
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interface is deprecated
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because it cannot be used correctly unless
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.Brq Va NAME_MAX
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is a fixed value.
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.Ef
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.Pp
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The
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.Fn opendir
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function
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opens the directory named by
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.Fa filename ,
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associates a
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.Em directory stream
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with it
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and
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returns a pointer to be used to identify the
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.Em directory stream
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in subsequent operations.
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The pointer
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.Dv NULL
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is returned if
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.Fa filename
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cannot be accessed, or if it cannot
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.Xr malloc 3
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enough memory to hold the whole thing.
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.Pp
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The
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.Fn fdopendir
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function is equivalent to the
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.Fn opendir
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function except that the directory is specified by a file descriptor
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.Fa fd
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rather than by a name.
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The file offset associated with the file descriptor at the time of the call
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determines which entries are returned.
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.Pp
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Upon successful return from
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.Fn fdopendir ,
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the file descriptor is under the control of the system,
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and if any attempt is made to close the file descriptor,
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or to modify the state of the associated description other than by means
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of
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.Fn closedir ,
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.Fn readdir ,
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.Fn readdir_r ,
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or
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.Fn rewinddir ,
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the behavior is undefined.
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Upon calling
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.Fn closedir
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the file descriptor is closed.
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The
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.Dv FD_CLOEXEC
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flag is set on the file descriptor by a successful call to
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.Fn fdopendir .
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.Pp
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The
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.Fn readdir
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function
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returns a pointer to the next directory entry.
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The directory entry remains valid until the next call to
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.Fn readdir
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or
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.Fn closedir
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on the same
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.Em directory stream .
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The function returns
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.Dv NULL
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upon reaching the end of the directory or on error.
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In the event of an error,
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.Va errno
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may be set to any of the values documented for the
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.Xr getdirentries 2
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system call.
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.Pp
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The
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.Fn readdir_r
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function
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provides the same functionality as
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.Fn readdir ,
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but the caller must provide a directory
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.Fa entry
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buffer to store the results in.
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The buffer must be large enough for a
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.Vt struct dirent
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with a
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.Va d_name
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array with
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.Brq Va NAME_MAX
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+ 1 elements.
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If the read succeeds,
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.Fa result
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is pointed at the
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.Fa entry ;
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upon reaching the end of the directory
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.Fa result
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is set to
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.Dv NULL .
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The
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.Fn readdir_r
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function
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returns 0 on success or an error number to indicate failure.
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.Pp
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The
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.Fn telldir
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function
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returns a token representing the current location associated with the named
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.Em directory stream .
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Values returned by
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.Fn telldir
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are good only for the lifetime of the
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.Dv DIR
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pointer,
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.Fa dirp ,
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from which they are derived.
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If the directory is closed and then
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reopened, prior values returned by
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.Fn telldir
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will no longer be valid.
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Values returned by
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.Fn telldir
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are also invalidated by a call to
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.Fn rewinddir .
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.Pp
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The
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.Fn seekdir
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function
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sets the position of the next
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.Fn readdir
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operation on the
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.Em directory stream .
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The new position reverts to the one associated with the
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.Em directory stream
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when the
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.Fn telldir
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operation was performed.
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.Pp
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The
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.Fn rewinddir
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function
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resets the position of the named
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.Em directory stream
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to the beginning of the directory.
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.Pp
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The
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.Fn closedir
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function
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closes the named
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.Em directory stream
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and frees the structure associated with the
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.Fa dirp
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pointer,
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returning 0 on success.
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On failure, \-1 is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Pp
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The
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.Fn fdclosedir
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function is equivalent to the
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.Fn closedir
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function except that this function returns directory file descriptor instead of
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closing it.
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.Pp
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The
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.Fn dirfd
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function
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returns the integer file descriptor associated with the named
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.Em directory stream ,
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see
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.Xr open 2 .
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.Pp
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Sample code which searches a directory for entry ``name'' is:
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.Bd -literal -offset indent
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dirp = opendir(".");
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if (dirp == NULL)
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return (ERROR);
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len = strlen(name);
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while ((dp = readdir(dirp)) != NULL) {
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if (dp->d_namlen == len && strcmp(dp->d_name, name) == 0) {
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(void)closedir(dirp);
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return (FOUND);
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}
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}
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(void)closedir(dirp);
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return (NOT_FOUND);
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.Ed
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.Sh SEE ALSO
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.Xr close 2 ,
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.Xr lseek 2 ,
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.Xr open 2 ,
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.Xr read 2 ,
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.Xr dir 5
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.Sh HISTORY
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The
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.Fn opendir ,
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.Fn readdir ,
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.Fn telldir ,
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.Fn seekdir ,
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.Fn rewinddir ,
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.Fn closedir ,
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and
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.Fn dirfd
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functions appeared in
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.Bx 4.2 .
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The
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.Fn fdopendir
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function appeared in
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.Fx 8.0 .
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.Fn fdclosedir
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function appeared in
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.Fx 10.0 .
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.Sh BUGS
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The behaviour of
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.Fn telldir
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and
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.Fn seekdir
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is likely to be wrong if there are parallel unlinks happening
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and the directory is larger than one page.
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There is code to ensure that a
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.Fn seekdir
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to the location given by a
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.Fn telldir
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immediately before the last
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.Fn readdir
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will always set the correct location to return the same value as that last
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.Fn readdir
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performed.
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This is enough for some applications which want to "push back the last entry read" E.g. Samba.
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Seeks back to any other location,
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other than the beginning of the directory,
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may result in unexpected behaviour if deletes are present.
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It is hoped that this situation will be resolved with changes to
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.Fn getdirentries
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and the VFS.
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