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



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  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 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 filesys-
       tems  and  large	 file  offsets.	  Consequently,	 Linux	2.4 added get-
       dents64(), with wider types for the d_ino and d_off fields.   In	 addi-
       tion, 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  follow-
       ing 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  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 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)

COLOPHON
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       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/.



Linux				  2015-04-12			   GETDENTS(2)