mirror of https://github.com/mkerrisk/man-pages
256 lines
6.9 KiB
Groff
256 lines
6.9 KiB
Groff
.\" Copyright (C) 1995 Andries Brouwer (aeb@cwi.nl)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Written 11 June 1995 by Andries Brouwer <aeb@cwi.nl>
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.\" Modified 22 July 1995 by Michael Chastain <mec@duracef.shout.net>:
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.\" Derived from 'readdir.2'.
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.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
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.TH GETDENTS 2 2008-11-11 "Linux" "Linux Programmer's Manual"
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.SH NAME
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getdents \- get directory entries
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.SH SYNOPSIS
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.nf
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.BI "int getdents(unsigned int " fd ", struct linux_dirent *" dirp ,
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.BI " unsigned int " count );
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.fi
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.SH DESCRIPTION
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This is not the function you are interested in.
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Look at
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.BR readdir (3)
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for the POSIX conforming C library interface.
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This page documents the bare kernel system call interface.
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.PP
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The system call
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.BR getdents ()
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reads several
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.I linux_dirent
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structures from the directory
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referred to by the open file descriptor
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.I fd
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into the buffer pointed to by
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.IR dirp .
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The argument
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.I count
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is specifies the size of that buffer.
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.PP
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The
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.I linux_dirent
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structure is declared as follows:
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.PP
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.in +4n
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.nf
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struct linux_dirent {
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unsigned long d_ino; /* Inode number */
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unsigned long d_off; /* Offset to next \fIlinux_dirent\fP */
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unsigned short d_reclen; /* Length of this \fIlinux_dirent\fP */
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char d_name[]; /* Filename (null-terminated) */
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/* length is actually (d_reclen \- 2 \-
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offsetof(struct linux_dirent, d_name) */
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/*
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char pad; // Zero padding byte */
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char d_type; // File type (only since Linux 2.6.4;
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// offset is (d_reclen \- 1))
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*/
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}
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.fi
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.in
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.PP
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.I d_ino
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is an inode number.
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.I d_off
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is the distance from the start of the directory to the start of the next
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.IR linux_dirent .
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.I d_reclen
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is the size of this entire
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.IR linux_dirent .
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.I d_name
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is a null-terminated filename.
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.I d_type
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is a byte at the end of the structure that indicates the file type.
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It contains one of the following values (defined in
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.IR <dirent.h> ):
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.TP 12
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.B DT_BLK
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This is a block device.
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.TP
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.B DT_CHR
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This is a character device.
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.TP
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.B DT_DIR
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This is a directory.
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.TP
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.B DT_FIFO
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This is a named pipe (FIFO).
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.TP
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.B DT_LNK
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This is a symbolic link.
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.TP
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.B DT_REG
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This is a regular file.
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.TP
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.B DT_SOCK
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This is a Unix domain socket.
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.TP
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.B DT_UNKNOWN
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The file type is unknown.
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.PP
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Currently,
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.\" kernel 2.6.27
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.\" The same sentence is in readdir.2
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only some file systems (among them: ext2, etx3, and ext4)
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have full support returning the file type in
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.IR d_type .
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All applications must properly handle a return of
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.BR DT_UNKNOWN .
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.SH "RETURN VALUE"
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On success, the number of bytes read is returned.
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On end of directory, 0 is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EBADF
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Invalid file descriptor
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.IR fd .
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.TP
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.B EFAULT
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Argument points outside the calling process's address space.
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.TP
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.B EINVAL
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Result buffer is too small.
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.TP
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.B ENOENT
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No such directory.
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.TP
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.B ENOTDIR
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File descriptor does not refer to a directory.
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.SH "CONFORMING TO"
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SVr4.
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.\" SVr4 documents additional ENOLINK, EIO error conditions.
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.SH NOTES
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Glibc does not provide a wrapper for this system call; call it using
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.BR syscall (2).
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You will need to define the
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.I linux_dirent
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structure yourself.
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This call supersedes
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.BR readdir (2).
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.SH EXAMPLE
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The program below demonstrates the use of
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.BR getdents ().
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The following output shows an example of what we see when running this
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program on an ext2 directory:
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.in +4n
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.nf
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.RB "$" " ./a.out /testfs/"
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--------------- nread=120 ---------------
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i-node# file type d_reclen d_off d_name
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2 directory 16 12 .
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2 directory 16 24 ..
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11 directory 24 44 lost+found
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12 regular 16 56 a
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228929 directory 16 68 sub
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16353 directory 16 80 sub2
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130817 directory 16 4096 sub3
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.fi
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.in
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.SS Program source
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\&
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.nf
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#define HAVE_D_TYPE /* Remove for kernels < 2.6.4 */
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#define _GNU_SOURCE
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#include <dirent.h> /* Defines DT_* constants */
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#include <fcntl.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <sys/stat.h>
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#include <sys/syscall.h>
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#define handle_error(msg) \\
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do { perror(msg); exit(EXIT_FAILURE); } while (0)
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struct linux_dirent {
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long d_ino;
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off_t d_off;
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unsigned short d_reclen;
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char d_name[];
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};
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#define BUF_SIZE 1024
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int
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main(int argc, char *argv[])
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{
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int fd, nread;
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char buf[BUF_SIZE];
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struct linux_dirent *d;
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int bpos;
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#ifdef HAVE_D_TYPE
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char d_type;
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#endif
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fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
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if (fd == \-1)
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handle_error("open");
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for ( ; ; ) {
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nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
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if (nread == \-1)
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handle_error("getdents");
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if (nread == 0)
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break;
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printf("\--------------- nread=%d ---------------\\n", nread);
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printf("i\-node# file type d_reclen d_off d_name\\n");
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for (bpos = 0; bpos < nread;) {
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d = (struct linux_dirent *) (buf + bpos);
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printf("%8ld ", d\->d_ino);
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#ifdef HAVE_D_TYPE
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d_type = *(buf + bpos + d\->d_reclen - 1);
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printf("%\-10s ", (d_type == DT_REG) ? "regular" :
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(d_type == DT_DIR) ? "directory" :
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(d_type == DT_FIFO) ? "FIFO" :
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(d_type == DT_SOCK) ? "socket" :
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(d_type == DT_LNK) ? "symlink" :
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(d_type == DT_BLK) ? "block dev" :
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(d_type == DT_CHR) ? "char dev" : "???");
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#endif
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printf("%4d %10lld %s\\n", d\->d_reclen,
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(long long) d\->d_off, (char *) d->d_name);
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bpos += d\->d_reclen;
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}
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}
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH "SEE ALSO"
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.BR readdir (2),
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.BR readdir (3)
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