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
       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 get-
       dents64(), 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 fol-
       lowing 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 appro-
       priately.

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 ---------------
", nread);
	       printf("inode#	 file type  d_reclen  d_off   d_name
");
	       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
", 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 4.15 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/.

Linux								    2017-09-15							       GETDENTS(2)