74f32f086b
- Add an ERRORS section for opendir(3) and closedir(3) - Document also the errors of readdir(3), readdir_r(3) and telldir(3) - Convert the code sample into an EXAMPLES section PR: 75711 Submitted by: abc <abc at ai1 dot anchorage dot mtaonline dot net> Reviewed by: 0mp, bcr, jilles Approved by: 0mp, bcr, jilles Obtained from: partial from OpenBSD MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D25892
404 lines
8.7 KiB
Groff
404 lines
8.7 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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.\" @(#)directory.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd August 1, 2020
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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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.Sh EXAMPLES
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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 ERRORS
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The
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.Fn opendir
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EACCES
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Search permission is denied for the component of the path prefix of
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.Fa filename
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or read permission is denied for
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.Fa filename .
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.It Bq Er ELOOP
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A loop exists in symbolic links encountered during resolution of the
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.Fa filename
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argument.
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.It Bq Er ENAMETOOLONG
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The length of the
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.Fa filename
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argument exceeds
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.Brq Dv PATH_MAX
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or
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a pathname component is longer than
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.Brq Dv NAME_MAX .
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.It Bq Er ENOENT
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A component of
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.Fa filename
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does not name an existing directory or
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.Fa filename
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is an empty string.
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.It Bq Er ENOTDIR
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A component of
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.Fa filename
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is not a directory.
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.El
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.Pp
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The
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.Fn fdopendir
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function will fail if:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument is not a valid file descriptor open for reading.
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.It Bq Er ENOTDIR
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The descriptor
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.Fa fd
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is not associated with a directory.
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.El
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.Pp
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The
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.Fn readdir
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and
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.Fn readdir_r
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functions may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr getdents 2 .
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.Pp
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The
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.Fn telldir
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function may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr realloc 3 .
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.Pp
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The
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.Fn closedir
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function may also fail and set
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.Va errno
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for any of the errors specified for the routine
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.Xr close 2 .
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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 STANDARDS
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The
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.Fn closedir ,
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.Fn dirfd ,
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.Fn fdopendir ,
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.Fn opendir ,
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.Fn readdir ,
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.Fn readdir_r ,
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.Fn rewinddir ,
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.Fn seekdir
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and
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.Fn telldir
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functions are expected to conform to
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.St -p1003.1-2008 .
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The
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.Fn fdclosedir
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function and the
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.Fa d_off ,
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.Fa d_reclen
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and
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.Fa d_type
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fields of
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.Vt struct dirent
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are non-standard, and should not be used in portable programs.
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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
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"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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