f14fb60209
* Updating common/lib * Updating lib/csu * Updating lib/libc * Updating libexec/ld.elf_so * Corrected test on __minix in featuretest to actually follow the meaning of the comment. * Cleaned up _REENTRANT-related defintions. * Disabled -D_REENTRANT for libfetch * Removing some unneeded __NBSD_LIBC defines and tests Change-Id: Ic1394baef74d11b9f86b312f5ff4bbc3cbf72ce2
400 lines
9.5 KiB
Groff
400 lines
9.5 KiB
Groff
.\" $NetBSD: directory.3,v 1.38 2012/10/08 18:15:09 njoly 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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.\" @(#)directory.3 8.1 (Berkeley) 6/4/93
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.\"
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.Dd October 15, 2011
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.Dt DIRECTORY 3
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.Os
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.Sh NAME
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.Nm fdopendir ,
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.Nm opendir ,
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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 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 * restrict dirp" "struct dirent * restrict entry" "struct dirent ** restrict 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 dirfd "DIR *dirp"
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.Sh DESCRIPTION
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The type
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.Vt DIR
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represents a directory stream;
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an ordered sequence of all directory entries in a particular directory.
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The purpose of the
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.Vt DIR
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structure is similar to that of the
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.Vt FILE
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structure maintained by the
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.Xr stdio 3
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library functions.
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.Sh FUNCTIONS
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The following standard directory operations are defined.
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.Bl -tag -width XXX
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.It Fn opendir "filename"
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The
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.Fn opendir
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function opens the directory named by
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.Fa filename
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and associates a directory stream with it.
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The directory stream is positioned at the first entry.
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Upon successful completion, a pointer to
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.Vt DIR
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type is returned.
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Otherwise,
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.Fn opendir
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returns
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.Dv NULL .
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.It Fn fdopendir "fd"
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The
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.Fn fdopendir
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function associates a directory stream with the directory file descriptor
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.Fa fd .
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The file offset associated with
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.Fa fd
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at the time of the call determines which entries are returned.
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.Pp
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Upon failure,
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.Fn fdopendir
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returns
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.Dv NULL .
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Otherwise 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,
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other than by means of
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.Fn closedir ,
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.Fn readdir ,
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.Fn readdir_r ,
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.Fn rewinddir ,
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the behavior is undefined.
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The file descriptor can be closed by calling
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.Fn closedir .
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.It Fn readdir "dirp"
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The
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.Fn readdir
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function returns a pointer to the directory entry at the current position
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in the directory stream specified by
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.Fa dirp ,
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and positions the directory stream at the next entry.
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It returns
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.Dv NULL
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upon reaching the end of the directory or detecting an invalid
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.Fn seekdir
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operation.
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The returned structure is described in
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.Xr dirent 3 .
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.Pp
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The returned pointer to the
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.Em dirent
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structure points to data which may be overwritten by another call to
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.Fn readdir
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on the same directory stream.
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This data is not however overwritten by another call to
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.Fn readdir
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on a different directory stream.
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.It Fn readdir_r "dirp" "entry" "result"
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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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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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Like
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.Fn readdir ,
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the
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.Fn readdir_r
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function may buffer several directory entries per actual read operation.
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Both functions mark for update the
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.Em st_atime
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field (see
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.Xr stat 2 )
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of the directory each time the directory is actually read.
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.It Fn telldir "dirp"
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The
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.Fn telldir
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function returns the current location associated
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with the directory stream specified by
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.Fa dirp .
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.Pp
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If the most recent operation on the particular directory stream was a
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.Fn seekdir ,
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the directory position returned from
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.Fn telldir
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is the same as
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.Fa loc
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supplied as an argument to the
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.Fn seekdir
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call.
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.It Fn seekdir "dirp" "loc"
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The
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.Fn seekdir
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function sets the position of the next
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.Fn readdir
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operation on the directory stream specified by
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.Fa dirp .
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The value of
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.Fa loc
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should come from a previous call to
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.Fn telldir
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using the same directory stream.
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.Pp
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The new position reverts to the one associated
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with the directory stream when the
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.Fn telldir
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operation was performed.
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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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.Vt 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 reopened, the
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.Fn telldir
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value cannot be re-used.
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.It Fn rewinddir "dirp"
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The
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.Fn rewinddir
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function resets the position of the named directory
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stream to the beginning of the directory.
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It also causes the directory stream to refer to the
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current state of the corresponding directory, as if a call to
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.Fn opendir
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would have been made.
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.Pp
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If
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.Fa dirp
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does not refer to a valid directory stream, the behavior is undefined.
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.It Fn closedir "dirp"
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The
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.Fn closedir
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function closes the 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 and \-1 on failure.
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.It Fn dirfd "dirp"
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The
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.Fn dirfd
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function returns the integer file descriptor
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associated with the directory stream specified by
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.Fa dirp .
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Upon failure,
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.Fn dirfd
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returns \-1.
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The returned file descriptor should be closed by
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.Fn closedir
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instead of
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.Xr close 2 .
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.Pp
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The rationale of
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.Fn dirfd
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is to provide a mechanism by which a file descriptor
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can be obtained for the use of the
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.Xr fchdir 2
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function.
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.El
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.Sh EXAMPLES
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Sample code which searches a directory for entry
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.Dq name
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is:
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.Bd -literal -offset indent
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len = strlen(name);
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dirp = opendir(".");
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if (dirp != NULL) {
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while ((dp = readdir(dirp)) != NULL)
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if (dp-\*[Gt]d_namlen == len \*[Am]\*[Am]
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!strcmp(dp-\*[Gt]d_name, name)) {
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(void)closedir(dirp);
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return (FOUND);
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}
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(void)closedir(dirp);
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}
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return (NOT_FOUND);
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.Ed
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.Sh COMPATIBILITY
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The described directory operations have traditionally been problematic
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in terms of portability.
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A good example is the semantics around
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.Sq \&.
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(dot) and
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.Sq \&..
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(dot-dot).
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Based on historical implementations,
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the rules about file descriptors apply to directory streams as well.
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The
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.St -p1003.1-2008
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standard does not however any more mandate that directory streams
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are necessarily implemented by using file descriptors.
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.Pp
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The following additional remarks can be noted from the
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.St -p1003.1-2008
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standard.
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.Bl -bullet -offset 2n
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.It
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If the type
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.Vt DIR
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is implemented using a file descriptor,
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like in
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.Nx ,
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applications should be able to open only
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.Dv OPEN_MAX
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files and directories.
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Otherwise the limit is left as unspecified.
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.It
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When a file descriptor is used to implement the directory stream, the
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.Fn closedir
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function behaves as if the
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.Dv FD_CLOEXEC
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had been set for the file descriptor.
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In another words, it is mandatory that
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.Fn closedir
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deallocates the file descriptor.
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.It
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If directory streams are not implemented by using file descriptors,
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functions such as
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.Fn dirfd
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may fail with
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.Er ENOTSUP .
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.It
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If a file is removed from or added to the directory
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after the most recent call to
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.Fn opendir
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or
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.Fn rewinddir ,
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it is unspecified whether a subsequent call to
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.Fn readdir
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returns an entry for that file.
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.It
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When using the function
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.Fn seekdir ,
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note that if the value of
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.Fa loc
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was not obtained from an earlier call to
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.Fn telldir ,
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or if a call to
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.Fn rewinddir
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occurred between the calls to
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.Fn telldir
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and
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.Fn seekdir ,
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any subsequent call to
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.Fn readdir
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is unspecified, possibly resulting undefined behavior.
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.It
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After a call to
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.Xr fork 2 ,
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either the parent or child (but not both) can continue processing the
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directory stream using
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.Fn readdir ,
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.Fn rewinddir ,
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or
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.Fn seekdir .
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However, if both the parent and child processes use these functions,
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the result is undefined.
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.El
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.Sh ERRORS
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.\"
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.\" XXX: The errors should be enumerated.
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.\"
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All described functions may set
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.Vt errno
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to indicate the error.
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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 dirent 3
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.Sh STANDARDS
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The
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.Fn opendir ,
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.Fn readdir ,
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.Fn rewinddir
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and
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.Fn closedir
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functions conform to
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.St -p1003.1-90 .
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The other functions conform to
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.St -p1003.1-2008 .
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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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.Nx 6.0 .
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