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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 inter-
       face.  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 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 before 2.6.3, attempting  to  access  this  field
       always provides the value 0 (DT_UNKNOWN).

       Currently, only some file systems (among them: Btrfs, ext2, etx3, and ext4) have full support for 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 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 this system call; call it using syscall(2).  You will need to define the
       linux_dirent structure yourself.

       This call supersedes readdir(2).

       Warning: Result of the getdents() system call in 32 bit application on 64 bit OS doesn't have to be always cor-
       rect, potentially the call itself can fail.

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, (char *) d->d_name);
                   bpos += d->d_reclen;
               }
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       readdir(2), readdir(3)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2009-07-04                       GETDENTS(2)