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GETDENTS(2)		   Linux Programmer's Manual		   GETDENTS(2)

NAME
       getdents	- get directory	entries

SYNOPSIS
       int getdents(unsigned int fd, struct linux_dirent *dirp,
		    unsigned int count);

       Note: There is no glibc wrapper for this	system call; see NOTES.

DESCRIPTION
       This is not the function	you are	interested in.	Look at	readdir(3) for
       the POSIX conforming C library interface.  This page documents the bare
       kernel system call interface.

       The  system  call getdents() reads several linux_dirent structures from
       the directory referred to by the	open file descriptor fd	into the  buf-
       fer  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 before 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 ap-
       plications must properly	handle a return	of DT_UNKNOWN.

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 appropri-
       ately.

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 this system	call;  call  it	 using
       syscall(2).   You  will need to define the linux_dirent structure your-
       self.  However, you probably want to use	readdir(3) instead.

       This call supersedes readdir(2).

       The original Linux getdents() system call did not handle	large filesys-
       tems  and  large	 file  offsets.	  Consequently,	 Linux	2.4 added get-
       dents64(), with wider types for the d_ino and d_off fields employed  in
       the linux_dirent	structure.

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 ---------------
	   i-node#  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("i-node#	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)

COLOPHON
       This  page  is  part of release 3.74 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
       http://www.kernel.org/doc/man-pages/.

Linux				  2012-08-03			   GETDENTS(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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