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-.\" Copyright (C) 1995 Andries Brouwer (aeb@cwi.nl)
-.\" and Copyright 2008, 2015 Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.\" Written 11 June 1995 by Andries Brouwer <aeb@cwi.nl>
-.\" Modified 22 July 1995 by Michael Chastain <mec@duracef.shout.net>:
-.\" Derived from 'readdir.2'.
-.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
-.\"
-.TH getdents 2 2024-02-25 "Linux man-pages 6.7"
-.SH NAME
-getdents, getdents64 \- get directory entries
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
-.B #include <unistd.h>
-.P
-.BI "long syscall(SYS_getdents, unsigned int " fd \
-", struct linux_dirent *" dirp ,
-.BI " unsigned int " count );
-.P
-.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
-.B #include <dirent.h>
-.P
-.BI "ssize_t getdents64(int " fd ", void " dirp [. count "], size_t " count );
-.fi
-.P
-.IR Note :
-glibc provides no wrapper for
-.BR getdents (),
-necessitating the use of
-.BR syscall (2).
-.P
-.IR Note :
-There is no definition of
-.I struct linux_dirent
-in glibc; see NOTES.
-.SH DESCRIPTION
-These are not the interfaces you are interested in.
-Look at
-.BR readdir (3)
-for the POSIX-conforming C library interface.
-This page documents the bare kernel system call interfaces.
-.SS getdents()
-The system call
-.BR getdents ()
-reads several
-.I linux_dirent
-structures from the directory
-referred to by the open file descriptor
-.I fd
-into the buffer pointed to by
-.IR dirp .
-The argument
-.I count
-specifies the size of that buffer.
-.P
-The
-.I linux_dirent
-structure is declared as follows:
-.P
-.in +4n
-.EX
-struct linux_dirent {
- unsigned long d_ino; /* Inode number */
- unsigned long d_off; /* Not an offset; see below */
- unsigned short d_reclen; /* Length of this \fIlinux_dirent\fP */
- char d_name[]; /* Filename (null\-terminated) */
- /* length is actually (d_reclen \- 2 \-
- offsetof(struct linux_dirent, d_name)) */
- /*
- char pad; // Zero padding byte
- char d_type; // File type (only since Linux
- // 2.6.4); offset is (d_reclen \- 1)
- */
-}
-.EE
-.in
-.P
-.I d_ino
-is an inode number.
-.I d_off
-is a filesystem-specific value with no specific meaning to user space,
-though on older filesystems it used to be
-the distance from the start of the directory to the start of the next
-.IR linux_dirent ;
-see
-.BR readdir (3) .
-.I d_reclen
-is the size of this entire
-.IR linux_dirent .
-.I d_name
-is a null-terminated filename.
-.P
-.I d_type
-is a byte at the end of the structure that indicates the file type.
-It contains one of the following values (defined in
-.IR <dirent.h> ):
-.TP 12
-.B DT_BLK
-This is a block device.
-.TP
-.B DT_CHR
-This is a character device.
-.TP
-.B DT_DIR
-This is a directory.
-.TP
-.B DT_FIFO
-This is a named pipe (FIFO).
-.TP
-.B DT_LNK
-This is a symbolic link.
-.TP
-.B DT_REG
-This is a regular file.
-.TP
-.B DT_SOCK
-This is a UNIX domain socket.
-.TP
-.B DT_UNKNOWN
-The file type is unknown.
-.P
-The
-.I d_type
-field is implemented since Linux 2.6.4.
-It occupies a space that was previously a zero-filled padding byte in the
-.I linux_dirent
-structure.
-Thus, on kernels up to and including Linux 2.6.3,
-attempting to access this field always provides the value 0
-.RB ( DT_UNKNOWN ).
-.P
-Currently,
-.\" kernel 2.6.27
-.\" The same sentence is in readdir.2
-only some filesystems (among them: Btrfs, ext2, ext3, and ext4)
-have full support for returning the file type in
-.IR d_type .
-All applications must properly handle a return of
-.BR DT_UNKNOWN .
-.SS getdents64()
-The original Linux
-.BR getdents ()
-system call did not handle large filesystems and large file offsets.
-Consequently, Linux 2.4 added
-.BR getdents64 (),
-with wider types for the
-.I d_ino
-and
-.I d_off
-fields.
-In addition,
-.BR getdents64 ()
-supports an explicit
-.I d_type
-field.
-.P
-The
-.BR getdents64 ()
-system call is like
-.BR getdents (),
-except that its second argument is a pointer to a buffer containing
-structures of the following type:
-.P
-.in +4n
-.EX
-struct linux_dirent64 {
- ino64_t d_ino; /* 64\-bit inode number */
- off64_t d_off; /* Not an offset; see getdents() */
- unsigned short d_reclen; /* Size of this dirent */
- unsigned char d_type; /* File type */
- char d_name[]; /* Filename (null\-terminated) */
-};
-.EE
-.in
-.SH RETURN VALUE
-On success, the number of bytes read is returned.
-On end of directory, 0 is returned.
-On error, \-1 is returned, and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-.TP
-.B EBADF
-Invalid file descriptor
-.IR fd .
-.TP
-.B EFAULT
-Argument points outside the calling process's address space.
-.TP
-.B EINVAL
-Result buffer is too small.
-.TP
-.B ENOENT
-No such directory.
-.TP
-.B ENOTDIR
-File descriptor does not refer to a directory.
-.SH STANDARDS
-None.
-.SH HISTORY
-SVr4.
-.\" SVr4 documents additional ENOLINK, EIO error conditions.
-.TP
-.BR getdents64 ()
-glibc 2.30.
-.SH NOTES
-glibc does not provide a wrapper for
-.BR getdents ();
-call
-.BR getdents ()
-using
-.BR syscall (2).
-In that case you will need to define the
-.I linux_dirent
-or
-.I linux_dirent64
-structure yourself.
-.P
-Probably, you want to use
-.BR readdir (3)
-instead of these system calls.
-.P
-These calls supersede
-.BR readdir (2).
-.SH EXAMPLES
-.\" FIXME The example program needs to be revised, since it uses the older
-.\" getdents() system call and the structure with smaller field widths.
-The program below demonstrates the use of
-.BR getdents ().
-The following output shows an example of what we see when running this
-program on an ext2 directory:
-.P
-.in +4n
-.EX
-.RB "$" " ./a.out /testfs/"
--\-\-\-\-\-\-\-\-\-\-\-\-\-\- nread=120 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
-inode# file type d_reclen d_off d_name
- 2 directory 16 12 .
- 2 directory 16 24 ..
- 11 directory 24 44 lost+found
- 12 regular 16 56 a
- 228929 directory 16 68 sub
- 16353 directory 16 80 sub2
- 130817 directory 16 4096 sub3
-.EE
-.in
-.SS Program source
-\&
-.\" SRC BEGIN (getdents.c)
-.EX
-#define _GNU_SOURCE
-#include <dirent.h> /* Defines DT_* constants */
-#include <err.h>
-#include <fcntl.h>
-#include <stdint.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <sys/syscall.h>
-#include <unistd.h>
-\&
-struct linux_dirent {
- unsigned long d_ino;
- off_t d_off;
- unsigned short d_reclen;
- char d_name[];
-};
-\&
-#define BUF_SIZE 1024
-\&
-int
-main(int argc, char *argv[])
-{
- int fd;
- char d_type;
- char buf[BUF_SIZE];
- long nread;
- struct linux_dirent *d;
-\&
- fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
- if (fd == \-1)
- err(EXIT_FAILURE, "open");
-\&
- for (;;) {
- nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
- if (nread == \-1)
- err(EXIT_FAILURE, "getdents");
-\&
- if (nread == 0)
- break;
-\&
- printf("\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- nread=%ld \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\en", nread);
- printf("inode# file type d_reclen d_off d_name\en");
- for (size_t bpos = 0; bpos < nread;) {
- d = (struct linux_dirent *) (buf + bpos);
- printf("%8lu ", d\->d_ino);
- d_type = *(buf + bpos + d\->d_reclen \- 1);
- printf("%\-10s ", (d_type == DT_REG) ? "regular" :
- (d_type == DT_DIR) ? "directory" :
- (d_type == DT_FIFO) ? "FIFO" :
- (d_type == DT_SOCK) ? "socket" :
- (d_type == DT_LNK) ? "symlink" :
- (d_type == DT_BLK) ? "block dev" :
- (d_type == DT_CHR) ? "char dev" : "???");
- printf("%4d %10jd %s\en", d\->d_reclen,
- (intmax_t) d\->d_off, d\->d_name);
- bpos += d\->d_reclen;
- }
- }
-\&
- exit(EXIT_SUCCESS);
-}
-.EE
-.\" SRC END
-.SH SEE ALSO
-.BR readdir (2),
-.BR readdir (3),
-.BR inode (7)
generated by cgit v1.2.3 (git 2.39.1) at 2024-10-31 11:10:07 +0000