getdents(2) - Linux manual page (original) (raw)
getdents(2) System Calls Manual getdents(2)
NAME top
getdents, getdents64 - get directory entriesLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <sys/syscall.h>** /* Definition of **SYS_*** constants */
**#include <unistd.h>**
**long syscall(SYS_getdents, unsigned int** _fd_**, struct linux_dirent ***_dirp_**,**
**unsigned int** _count_**);**
**#define _GNU_SOURCE** /* See feature_test_macros(7) */
**#include <dirent.h>**
**ssize_t getdents64(int** _fd_**, void** _dirp_**[.**_count_**], size_t** _count_**);**
_Note_: glibc provides no wrapper for **getdents**(), necessitating the
use of [syscall(2)](../man2/syscall.2.html).
_Note_: There is no definition of _struct linuxdirent_ in glibc; see
NOTES.DESCRIPTION top
These are not the interfaces you are interested in. Look at
[readdir(3)](../man3/readdir.3.html) for the POSIX-conforming C library interface. This
page documents the bare kernel system call interfaces.getdents() The system call getdents() reads several linuxdirent structures from the directory referred to by the open file descriptor fd into the buffer pointed to by dirp. The argument count specifies the size of that buffer.
The _linuxdirent_ structure is declared as follows:
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 _linuxdirent_ */
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)
*/
}
_dino_ is an inode number. _doff_ 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 _linuxdirent_; see [readdir(3)](../man3/readdir.3.html).
_dreclen_ is the size of this entire _linuxdirent_. _dname_ is a
null-terminated filename.
_dtype_ is a byte at the end of the structure that indicates the
file type. It contains one of the following values (defined in
_<dirent.h>_):
**DT_BLK** This is a block device.
**DT_CHR** This is a character device.
**DT_DIR** This is a directory.
**DT_FIFO**
This is a named pipe (FIFO).
**DT_LNK** This is a symbolic link.
**DT_REG** This is a regular file.
**DT_SOCK**
This is a UNIX domain socket.
**DT_UNKNOWN**
The file type is unknown.
The _dtype_ field is implemented since Linux 2.6.4. It occupies a
space that was previously a zero-filled padding byte in the
_linuxdirent_ structure. Thus, on kernels up to and including
Linux 2.6.3, attempting to access this field always provides the
value 0 (**DT_UNKNOWN**).
Currently, only some filesystems (among them: Btrfs, ext2, ext3,
and ext4) have full support for returning the file type in
_dtype_. All applications must properly handle a return of
**DT_UNKNOWN**.getdents64() The original Linux getdents() system call did not handle large filesystems and large file offsets. Consequently, Linux 2.4 added getdents64(), with wider types for the dino and doff fields. In addition, getdents64() supports an explicit dtype field.
The **getdents64**() system call is like **getdents**(), except that its
second argument is a pointer to a buffer containing structures of
the following type:
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) */
};RETURN VALUE top
On success, the number of bytes read is returned. On end of
directory, 0 is returned. On error, -1 is returned, and _[errno](../man3/errno.3.html)_ is
set to indicate the error.ERRORS top
**EBADF** Invalid file descriptor _fd_.
**EFAULT** Argument points outside the calling process's address
space.
**EINVAL** Result buffer is too small.
**ENOENT** No such directory.
**ENOTDIR**
File descriptor does not refer to a directory.STANDARDS top
None.HISTORY top
SVr4.
**getdents64**()
glibc 2.30.NOTES top
glibc does not provide a wrapper for **getdents**(); call **getdents**()
using [syscall(2)](../man2/syscall.2.html). In that case you will need to define the
_linuxdirent_ or _linuxdirent64_ structure yourself.
Probably, you want to use [readdir(3)](../man3/readdir.3.html) instead of these system
calls.
These calls supersede [readdir(2)](../man2/readdir.2.html).EXAMPLES top
The program below demonstrates the use of **getdents**(). The
following output shows an example of what we see when running
this program on an ext2 directory:
$ **./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 sub3Program source
#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 <sys/types.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 ---------------\n", nread);
printf("inode# file type d_reclen d_off d_name\n");
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\n", d->d_reclen,
(intmax_t) d->d_off, d->d_name);
bpos += d->d_reclen;
}
}
exit(EXIT_SUCCESS);
}SEE ALSO top
[readdir(2)](../man2/readdir.2.html), [readdir(3)](../man3/readdir.3.html), [inode(7)](../man7/inode.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.9.1 2024-06-15 getdents(2)
Pages that refer to this page:readdir(2), syscalls(2), readdir(3), proc(5), proc_pid_task(5)