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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);

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 is 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.

       Currently,  only	 some  file systems (among them: ext2, etx3, and ext4)
       have full support returning the file type in d_type.  All  applications
       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.

       This call supersedes 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 ---------------
	   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 HAVE_D_TYPE     /* Remove for kernels < 2.6.4 */
       #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;
       #ifdef HAVE_D_TYPE
	   char d_type;
       #endif

	   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);
       #ifdef HAVE_D_TYPE
		   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" : "???");
       #endif
		   printf("%4d %10lld  %s\n", d->d_reclen,
			   (long long) d->d_off, (char *) d->d_name);
		   bpos += d->d_reclen;
	       }
	   }

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       readdir(2), readdir(3)

COLOPHON
       This  page  is  part of release 3.15 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2008-11-11			   GETDENTS(2)
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