GETDENTS
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
getdents, getdents64 - get directory entries
SYNOPSIS
int getdents(unsigned int fd, struct linux_dirent *dirp,
unsigned int count);
int getdents64(unsigned int fd, struct linux_dirent64 *dirp,
unsigned int count);
Note:
There are no glibc wrappers for these system calls; see NOTES.
DESCRIPTION
These are not the interfaces you are interested in.
Look at
readdir(3)
for the POSIX-conforming C library interface.
This page documents the bare kernel system call interfaces.
getdents()
The system call
getdents()
reads several
linux_dirent
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
linux_dirent
structure is declared as follows:
struct linux_dirent {
unsigned long d_ino; /* Inode number */
unsigned long d_off; /* Offset to next linux_dirent */
unsigned short d_reclen; /* Length of this linux_dirent */
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)
*/
}
d_ino
is an inode number.
d_off
is the distance from the start of the directory to the start of the next
linux_dirent.
d_reclen
is the size of this entire
linux_dirent.
d_name
is a null-terminated filename.
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
<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
d_type
field is implemented since Linux 2.6.4.
It occupies a space that was previously a zero-filled padding byte in the
linux_dirent
structure.
Thus, on kernels up to and including 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
d_type.
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
d_ino
and
d_off
fields.
In addition,
getdents64()
supports an explicit
d_type
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; /* 64-bit offset to next structure */
unsigned short d_reclen; /* Size of this dirent */
unsigned char d_type; /* File type */
char d_name[]; /* Filename (null-terminated) */
};
RETURN VALUE
On success, the number of bytes read is returned.
On end of directory, 0 is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- 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.
CONFORMING TO
SVr4.
NOTES
Glibc does not provide a wrapper for these system calls; call them using
syscall(2).
You will need to define the
linux_dirent
or
linux_dirent64
structure yourself.
However, you probably want to use
readdir(3)
instead.
These calls supersede
readdir(2).
EXAMPLE
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 sub3
Program source
#define _GNU_SOURCE
#include <
dirent.h> /* Defines DT_* constants */
#include <
fcntl.h>
#include <
stdio.h>
#include <
unistd.h>
#include <
stdlib.h>
#include <
sys/stat.h>
#include <
sys/syscall.h>
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
struct linux_dirent {
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, nread;
char buf[BUF_SIZE];
struct linux_dirent *d;
int bpos;
char d_type;
fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
if (fd == -1)
handle_error("open");
for ( ; ; ) {
nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
if (nread == -1)
handle_error("getdents");
if (nread == 0)
break;
printf("--------------- nread=%d ---------------\n", nread);
printf("inode# file type d_reclen d_off d_name\n");
for (bpos = 0; bpos < nread;) {
d = (struct linux_dirent *) (buf + bpos);
printf("%8ld ", 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 %10lld %s\n", d->d_reclen,
(long long) d->d_off, d->d_name);
bpos += d->d_reclen;
}
}
exit(EXIT_SUCCESS);
}
SEE ALSO
readdir(2),
readdir(3),
inode(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- getdents()
-
- getdents64()
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- Program source
-
- SEE ALSO
-
- COLOPHON
-
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